PHYTOPLANKTON COMPOSITION AND ABUNDANCE IN LAKE ONTARIO DURING IFYGL E. F. Stoermer, M. M. Bowman, J. C. Kingston and A. L. Schaedel Final Report U.S. Environmental Protection Agency Research Grant R-800605 Special Report No. 53 Great Lakes Research Division The University of Michigan Ann Arbor, Michigan 1974 ABSTRACT Based, on samples collected during the International Field Year for the Great Lakes, the phytoplankton assemblage of Lake Ontario is dominated by taxa indicative of degraded water quality, including many potentially nuisance producing species. Many taxa characteristic of the offshore waters of the upper Great Lakes are either absent from the flora or very rare. Compared to the upper lakes, the flora of Lake Ontario undergoes extreme seasonal succession, with diatoms predominating during the winter and early spring, green algae becoming abundant during the summer, and blue-green algae showing a distinct fall peak. Various species of micro- flagellates are a relatively important element of the flora during all seasons. Succession during the spring bloom appears to be controlled by the thermal bar, and our data suggest control by depletion of essen- tial nutrients following stratification. Striking differences were apparent in samples collected on comparable dates in the spring of two successive years. These differences apparently result from exceptional weather conditions which prevailed during the first sampling period. The distribution of species particularly tolerant of disturbance appear- ed to be controlled by both proximity to major population centers and lake morphometry. The abundance of halophilic species in most pro- ductive areas suggests effects of conservative ion contamination as well as nutrient enrichment. Xll CONTENTS CONCLUSIONS AND RECOMMENDATIONS 1 INTRODUCTION 3 MATERIALS AND METHODS 9 Particle Count Samples 9 Phytoplankton Population Analysis . 9 Archival Plankton Collections 10 Reference Chlorophyll Samples 10 RESULTS 13 Chlorophyll Values at Master Stations 13 Particle Count Data . .17 Areal distribution by size class 19 Vertical distribution by size class 66 Phytoplankton Data 114 Areal distribution of total phytoplankton in near-surface waters 114 Areal distribution of major groups in near-surface waters 120 Diversity trends in near-surface waters 128 Areal distribution of selected species 13A Bacillariophyta 134 Chlorophyta 236 Cyanophyta 278 Cryptophyta 317 Pyrrophyta 317 Microf lagellates 328 Vertical distribution of phytoplankton at master stations „ 339 DISCUSSION 363 REFERENCES 369 FIGUEES Page 1. Primary station locations ^ 2. Vertical distribution of Chlorophyll a at master stations ... 14 3. Areal distribution of 5-10 um particles 21 4. Areal distribution of 10-20 ym particles 30 5. Areal distribution of 20-40 ym particles 40 6. Areal distribution of 40-80 ym particles . 49 7. Areal distribution of 80-150 ym particles 58 8. Vertical distribution of 5-10 ym particles 67 9. Vertical distribution of 10-20 ym and 20-40 ym particles ... 83 10. Vertical distribution of 40-80 ym and 80-150 ym particles ... 99 11. Areal distribution of total cell counts 115 12. Seasonal average abundance of major phytoplankton group cell counts 121 13. Areal distribution of major phytoplankton group cell counts . . 122 14. Assemblage diversity (Shannon-Weaver index) 129 15. Distribution of Asterionella formosa 135 16. Distribution of Cosainodisous subsalsa 141 17. Distribution of diatoma tenue var. elongatwn 146 18. Distribution of Fvagitaria aapuoina 152 19. Distribution of Fragilaria arotonensis 158 20. Distribution of Melosira islandioa 164 21. Distribution of Nitzsahia hacata 169 22. Distribution of Nitzsehia dissipata 175 23. Distribution of Nitzsahia sp . (#2) 181 24. Distribution of Stephanodisaus alpinus 186 25. Distribution of Stephanodisaus bindevanus ^ .... 192 26. Distribution of Stephanodisaus hantzsohii 198 27. Distribution of Stephanodisaus minutus 203 28. Distribution of Stepha-nn discus subtilis 209 29. Distribution of Stephanodisaus tenuis 214 30. Distribution of SicrireVla angusta 220 31. Distribution of Synedva ostenfeldii 226 32. Distribution of Tahellaria fenestrate 231 33. Distribution of Ankistrodesmus falaatus 237 34. Distribution of Botryoaoaaus braunii. • . 243 35. Distribution of Coelastrum miaroporum 244 36. Distribution of Gloeaystis planotoniaa 249 37. Distribution of Ooaystis spp 254 38. Distribution of Pediastrum glandulifevum 259 39. Distribution of Phaaotus lentioularis 261 40. Distribution of Saenedesmus bioellularis ........... 265 41. Distribution of Saenedesmus quadriaauda var. longispina .... 271 42. Distribution of Saenedesmus quadriaauda var. quadrispina • • • 276 43. Distribution of Ulotkrix spp. 279 44. Distribution of Anabacria flos-aquae • • 284 45. Distribution of Anabaerta variabilis 287 46. Distribution of Anaaystis ayanea ..... 290 vi Page 47. Distribution of Anaoystis -incerta 296 48. Distribution of Aphanizomenon flos-aquae .301 49. Distribution of Gomphosphaeria aponina . 304 50. Distribution of Gomphosphaeria laaustris 305 51. Distribution of Gomphosphaeria wiohurae 307 52. Distribution of Oscillatoria lirnnetioa 312 53. Distribution of Cryptomonas erosa 318 54. Distribution of GZenodiniim and Gymnodinium 323 55. Distribution of Peridinitm spp 329 56. Distribution of microf lagellates 334 57. Vertical distribution of total phytoplankton cell counts at master stations 344 58. Vertical distribution of diatoms at master stations . . .... 348 59. Vertical distribution of green algae at master stations .... 352 60. Vertical distribution of blue-green algae at master stations 356 61. Vertical distribution of microflagellates at master stations , 359 vii TABLES 1. Format for phytoplankton species information 7 2. Format for particle count information 8 3. Example of label for archival samples 8 4. Correlations between f luorometrically determined chlorophyll a values and particle counts for all depths at master stations 18 5. Correlation coefficients for EPA spectrometrically determined chlorophyll a values and: (1) f luoro- metrically determined chlorophyll a values (master stations only), (2) 10-20 ym particle counts, (3) 20-40 pm particle counts, (4) total cell counts 20 6. Correlation between f luorometrically determined chlorophyll a values and cell counts, in total and by category at master stations 341 7. Correlation of particle counts in channels measured with cell counts as determined by visual identification for master stations 341 vili CONCLUSIONS AND RECOMMENDATIONS 1. The phytoplankton flora of Lake Ontario is qualitatively and quan- titatively dissimilar from all but the most severely impacted re- gions of the upper Great Lakes. It would appear appropriate to develop separate predictive models for the lower (Erie and Ontario) and upper (Huron, Michigan and Superior) Great Lakes, 2. Ouir data suggest that there are considerable yearly differences in the abundance and composition of the phytoplankton assemblage in Lake Ontario, apparently related to weather conditions during the spring phytoplankton maximum. Data from IFYGL biology and chemistry projects should be in- terpreted with caution, especially as a basis for projections. Any further projects of this type should be designed to pro- vide a multi-year data base. Local effects of major population concentrations are evident in both the composition and abundance of the phytoplankton flora, how- ever integrated, lake-wide effects appear to be strongly controlled by morphometry. Predictive models should account for morphometric effects. Although this project does not provide direct evidence, patterns of phytoplankton abundance and succession in Lake Ontario are consis- tent with the hypothesis that phosphorus is the primary nutrient controlling productivity in the system. It appears that limitation of phosphorus loadings is an appropriate first management strategy. The phytoplankton flora of most productive regions of Lake Ontario is dominated by halophilic species. Greater emphasis should be placed on reduction of conservative element contamination, as well as nutrient limitation. Lack of a sufficient historic data base restricts interpretation of present results in the context of long-term trends within the Lake Ontario system, except by analogy to better studied comparable systems. Effort should be made to develop such comparative data, either by recovery and analysis of historic samples or by paleolimno- logic methods. 7. The phytoplankton assemblage of Lake Ontario appears to be highly unstable, on both a seasonal and yearly basis. It is suggested that, due to this unstable food base, fisheries management practices successful in the upper Great Lakes may prove less productive if adopted in Lake Ontario. (Conclusions regarding particular taxa and general conditions in Lake Ontario are discussed in more detail in summary section beginning on p. 363 following.) INTRODUCTION This project was initiated as part of an integrated series of investi- gations of Lake Ontario under the general aegis of the International Field Year for the Great Lakes. The Field Year was conceived primarily as an attempt to construct a precise model of the hydrological character- istics of Lake Ontario. Since it was early recognized that the unique bank of physical data generated would have great utility in constructing a more general process model of the Lake Ontario ecosystem, the original concept was modified to include biological and chranical measurements appropriate to the construction of the more general model. The general plan has been published (IFYGL 1972) and need not be discussed here. It is important to keep in mind, however, that the biological and chemical sampling effort was carried out largely within the constraints of the original project concept. It will be apparent also that the original plan underwent evolutionary changes during the course of the project, some of which were imposed by operational constraints in sampling platform availability and operational capabilities. Of perhaps greater importance were modifications of the original sampling plan in response to the effects of a major meteorological "accident." June 1972 was one of the coldest and wettest Junes on record in the Lcike Ontario basin. Near the end of this extremely atypical month, significant portions of the region were subjected to the fringe effects of Tropical Storm Agnes (Atmospheric Environment Service 1972) which resulted in record rainfalls at many stations within the Lake Ontario drainage basin. Since early results of several projects indicated significant effects of these events, the originally conceived sampling plan was considerably extended to provide comparison between the spring sampling periods in two successive years. One of the primary objectives of the project was to obtain quasi-synoptic coverage of the entire lake during successive time intervals represent- ing periods of characteristic seasonal succession of biological popula- tions within the lake. Some emphasis was placed on the early spring period, which has the highest seasonal standing crop of primary producer organisms in most temperate lakes. The 60 primary stations sampled are shown in Figure 1. During May 1972, sampling of these stations was only about 50% effective due to weather- induced operational restrictions on the sampling platform utilized. Sampling during 1973 was on a somewhat more restricted basis. Nominally 40 of the 60 original stations were chosen, but operational problems associated with severe winter weather resulted in the omission of a limited number of stations on certain cruises. In all cases arbitrarily specified depths were sampled. Depths selected were 1, 5, 10, 15, 20, 25, 30, 40, 50, 100, 150 and 200 m. In cases where depth at the station sampled did not permit a full 12-bottle cast, sampling profile was truncated to the nearest specified depth and an additional sample was taken about 5 m above bottom. Depths sampled are Indicated in summary plots of vertical profile information following. 0) H U l-i •H U 03 c o •H ■U cfl 4J CO u ^ U CO a •H o M Acquisition and interpretation of phytoplankton population information suitable for use in a project of this size presents certain problems which have never been completely solved. Perhaps the most serious difficulty is that identifications are not possible by other than manual methods. This means that analysis of samples, under the best of conditions, proceeds quite slowly and is subject to human errors which are difficult to control. The problem is compounded in the present instance by the fact that the phytoplankton of the Laurentian Great Lakes is rather poorly known, and standard references covering the taxonomic groups of greatest interest are not avialable. It is thus necessary, to a substantial degree, to treat with some rather fundamen- tal taxonomic problems during the course of such an investigation. Because of the strong seasonal succession of phytoplankton communities, unique problems arise during each successive sampling during a year's period. This entire problan is further compounded by the diversity of groups present and their basic biochemical differences. Because of these differences, no single preservation technique is completely suitable for all organisms which may be encountered in any sample. There are many organisms present in the phytoplankton of Lake Ontario which can only be identified with any degree of confidence in the living condition. When treating with the number of samples generated by the IF^GL project, it is exceedingly difficult to treat every sample with all methods necessary to assure the best treatment of every taxonomic group which could conceivably be present in a given sample. This is especially true in the case of organisms which are best identified in the brief time they remain viable after collection. As a practical matter it is usually necessary to make some compromise between the amount of data coverage, in terms of samples taken, and data quality, in te;nns of complete and confident identifications. In this project we placed primary emphasis on development of infoirmation regarding the abundance and distribution of particular populations. Because of the necessity to process samples rapidly into a form where they could be stored for considerable periods of time before final analysis, we chose to prepare these samples as senii-permanent micro- scope slides. In order to extend the sample coverage, we also made a rapid automated analysis of particles present in the waters sampled according to size class. While this measurement does not allow the identification of particular populations or even, necessarily, the segregation of phyto- plankton from other classes of particles occurring in the water, we felt that comparison of trends in such measurements with population information and gross biomass estimates developed by other projects might serve to extend the usefulness of both types of observations. Because of the current unsatisfactory state of taxonomic treatments of Lake Ontario phytoplankton, we felt it highly desirable that one of the outputs of IFYGL should be a coherent set of reference samples from the lake which might serve as the basis for revisionary work on certain groups by specialists. Such archival samples are also highly desirable as a means of checking results of the project and to provide a means of extending observations should this become desirable. Such reference samples also, in a sense, serve to provide a standard against which future changes in the Lake Ontario ecosystem may be judged. In this project we also collected and analyzed a limited number of chlorophyll samples from IFYGL biology-chemistry master stations. This effort was partially motivated by the desire to be able to compare these values, which were fluorometrically determined, with spectrometrically determined values from these stations by other projects. These samples were also used to inspect correlations between this measure of standing crop and the particle count and population counts generated by this project in its initial phases, before the more extensive set of spectrometrically determined chlorophyll values developed by other projects was available. Summarization of the infomnation developed by this project presents some problems. Since the information is to be included in further efforts to develop a model of the Lake Ontario ecosystem, it is necessary to include the original semi-reduced data in an easily available format. This material is too extensive to be conveniently reproduced in the standard report format. In the interests of economy and to reduce errors of transcription, we have submitted the semi-reduced digital Information on magnetic tape to the project officer together with one complete hard-copy printout. Printout format for the species count information is shown in Table 1 and for the particle count information in Table 2. A summary listing of labels for archival samples has been provided to the project officer, and an example of the label informa- tion is given in Table 3. Graphic summaries of this information are presented in the results section following. The summaries include representations of abundance of particles by size class for the seasons sampled, of total phytoplankton abundance, the abundance of most common major taxonomic divisions, and the distribution of some of the more important or interesting species and genera. TABLE 1. Format for phytoplankton species information. lake Ontario (IFYGL) , station 95-All Depths year: 1973 station: 96 latitude: 430 58.fl« nuBber of cells counted: 1258 diversity: 2.U0U Julian day: depth: longitude: Tolune of water scanned: evenness: 80 (21 >1ar» 76" U0.8' 3.477 ml 0.688 division Cyanophyta (blue-green algae) Chlorophyta (green alqae) . Bacillariophyta (diatoms) . Chrysophyta (chrysophytos) . Cryptophyta (cryptomonads) . Pyrrophyta (dinof lagella tes) other i^ndeter ained number of species cells/ml total 1 4 22 1 1 2 ..Z 33 12.6 127.8 2308.0 33. S 14.7 31.4 0.0 „ ,.106.8 2634.7 SE . 8.4 10.5 276.5 33.5 10.5 2.1 0.0 397.9 CV X pop. 0.67 0.08 0.12 1.00 0.71 0.07 **** 0.73 0.477 4.84 9 87.599 1,272 0.556 1.192 0.0 a. 054 0.15 100.000 species name cells/al SS CV % pop. Stephanodiscus subtilis .... 670.2 41.9 0.06 25.437 Usterionella formosa 580.1 23.0 0.04 22.019 Stephanodiscus ninutus 261.8 10.5 0.04 9.936 Stephanodiscus tenuis - - 245.0 27.2 0.11 9.300 Stephanodiscus hantzschii 209.4 58.6 0.28 7.949 Helosira islandica 100.5 46.1 0.45 3.316 aiothrix sp. t1 85.9 14.7 0.17 3.259 Ondetermined flagellate sp. #1 81.7 81.7 1.00 3.100 Stephanodiscus alpinus 44.0 2.1 0.05 1.669 Tabellaria fenestrata 37.7 16.8 0.44 1.431 Diatona tenue var. elongatum 35.6 23.0 0.65 1.351 Synura uvella 33.5 33.5 1.00 1.272 Stephanodiscus binderanus ......... 29.3 8.4 0.29 1.113 Scenedesmus bicellularis 27.2 6.3 0.23 1.033 Ondetermined flagellate sp. #2 25.1 4.2 0.17 0.954 Peridiniua sp. #1 25.1 4.2 0.17 0.954 Surirella angusta 23.0 2.1 0.09 0.874 Sitzschia bacata 16.8 4.2 0.25 0.636 Cryptoiaonas sd. »1 14.7 10.5 0.71 Sitzschia dissipata 14.7 6.3 0.43 Oscillatoria limaetica 12.6 8.4 0.67 SnlcistrodestDus sp. »1 8.4 4.2 0.5'^ Pragilaria crotonensis 8.4 8.4 1.00 Hit-irschia sp. »2 8.4 0.0 0.0 Cyabell^ turgida var. pseudogracilis. ... 6.3 2.1 0.33 Dinof lagollate sp. »1 6.3 6.3 1.00 Phacotus sp. »1 6.3 2.1 0.33 Wavicula monisculus var. upsaliensis. . . . 4.2 0.0 0.0 Nitzschia filifornis 4.2 4.2 1.00 Rchnanthos clevei 2.1 2.1 1.00 Amphora ovalis 2.1 2,1 1.00 Navicula tripunctata. 2.1 2.1 1.00 Rhoicosphenia curvata 2.1 2.1 1.00 J.C79 556 ,556 ,477 .313 0.313 0.313 0,239 0.2 38 0.238 0. 159 0.159 0.C79 0.079 0.079 TABLE 2. Format for particle count information. LAKE ONTARIO PARTICLE COUNTS IPARTlCLES/100 HL» CRUISE 7 JU^ IE 12 - , JUNE 16 ., 1972 sia OFP PARTICLE SIZES !IN MICRONS) « 5M} 5-10 10-20 20-40 40-80 80-1! i 1 97247 23044 2053 98 8 1 5 104374 25281 1895 82 3 10 95736 23978 2249 135 14 IS 97873 27320 2387 123 7 20 50819 19292 1194 36 7 25 44788 14890 780 40 3 30 52286 11752 530 60 10 2 1 98525 23623 3593 144 11 2 5 116173 24859 2646 172 10 2 10 117907 19870 1655 228 21 3 1 115860 24860 2122 225 23 3 5 115772 27945 2718 201 17 3 10 114153 25469 2431 169 12 3 12 87514 23868 2229 187 13 5 1 95381 38328 5031 193 10 5 5 84475 33454 4846 382 35 5 10 75784 246 86 2985 147 10 TABLE 3. Example of label for archival samples. IFYGL Lake Ontario 500 ml raw water sample thiru GFC filt. preserv. 6H20: 3 ETOH: 1 HCHO Dr. Eugene Stoermer, U. of Mich. DATE: 1 NOV 72 STATION: 52 SAMPLE NO.: 1869 DEPTH: 1 m MATERIALS AND METHODS All samples were collected by Niskln Bottle cast using a multiple bottle rosette sampler. In all cases discrete splits of the initial 5-liter samples were taken by ship technical personnel and delivered to project personnel for further processing. Preservation and processing of samples were initiated immediately, and all samples were preserved with- in 1/2 hr of collection. The only exceptions were discrete, small-voltmie samples retained for immediate observation of living phytoplankton, which were discarded without further processing after observations were completed. PARTICLE COUNT SAMPLES Samples for particle count analysis were taken in 125 ml polypropylene bottles pre-spiked with sufficient commercial formalin to give final concentration of approximately 1%. Early in the project some problems were experienced with polymerization of the small volumes of formalin used after prolonged storage, but this was corrected by reducing storage time of spiked bottles to less than 10 days. After collection and preservation, samples were returned to the laboratory without further treatment. Samples were analyzed by passing 100 ml volumes through a HIAC optical occlusion particle counter fitted with a 5-150 ^im counting head. Samples were gently and uniformly agitated before analysis to assure uniform suspension of particles. Results of single, initial runs are reported since it was discovered that results of multiple runs showed a reduc- tion in readings in larger size channels and an increase in smaller size channels, apparently resulting from mechanical disruption of the larger phytoplankton colonies and detrital aggregates. In all cases the machine was adjusted to read in channels with nominal size of 5-10, 10-20, 20-40, 40-80, and 80-150 ym, according to manufacturer's specifications. Complete records of particle count results have been submitted to the project officer on magnetic tape. Summary plots of this information are given in the results section following. PHYTOPLANKTON POPULATION ANALYSIS Saro^ples for phytoplankton population analysis were taken as a 150 ml split of the original 5-liter Niskin Bottle cast. These subsamples were immediately fixed with glutaraldehyde (4% by volume) and stored in the dark at approximately 4°C for at least 4 hr and not longer than 8 hr to assure complete fixation. After fixation, sample bottles were gently agitated to assure resuspension of phytoplankton present and a 50 ml volume was withdrawn for further processing. Material was concentrated by filtration onto 25 mm "AA" Millipore filters, partially dehydrated through an ethanol series and embedded in beechwood creosote. Prepared filters were mounted on 50 x 75 mm glass slides and covered with a 43 x 50 mm #1 cover glass. Preparations were allowed to dry for approximately two weeks, during which time embedding medium lost by volatilization was periodically replaced, then the edges of the cover glasses were sealed with paraffin. Material was analyzed by visual counts of phytoplankton cells present using Leitz Ortholux microscopes fitted with fluorite oil immersion objectives giving approximately 1250X magnification and nominal Numerical Aperture of 1.32. Population estimates given are the average of two 10-mm radial strips counted, corrected for volume. Effective filtration diameter in the filtration apparatus used is 20 mm. Raw counts were encoded in computer compatible format on punched cards. Subsequent data sorting and manipulation were computerized. Hard-copy data summaries in the format shown in Table 1 are available for all samples counted . Summaries include estimates of absolute frequency, relative frequency, and error associated with these quantities. Assemblage parameters calculated include estimates of diversity and evenness as well as total assemblage abundance and the contribution of the several major Divisions. Summary information in the results section following is machine-plotted from reduced data stored on magnetic tape. Intermediate programs are utilized to compile and call data of particular interest for plotting routines or for further processing. ARCHIVAL PLANKTON COLLECTIONS Archival samples were taken as 500-ml subsamples of the original 5-liter Niskin Bottle cast. Subsamples were Immediately filtered onto 47-mm Watten "GFC" glass fiber filters, placed in 5-dram amber glass capsule vials, and preserved in a mixture of 6 parts water of collection, 3 parts 95% ethanol, and 1 part commercial formalin. Vials were then sealed and temporarily labeled for return to the laboratory. In the laboratory, vials were inspected and additional preservative added if needed, and then permanently labeled with computer-generated labels of the type shown in Table 3. Finally vial caps were sealed with paraf- fin to assure against loss of preservative. REFERENCE CHLOROPHYLL SAMPLES Samples for chlorophyll analysis were taken as 250-ml splits of original 5-1 Niskin Bottle casts at IFYGL master stations only. Sub- samples were immediately filtered onto 47-mm diameter HA Millipore filters and placed in 5-dram amber glass capsule vials containing 10 ml of 90% acetone, labeled and stored in the dark at approximately 0°C. 10 Samples were analyzed after return to the laboratory and usual storage/ extraction times were on the order of 6 days. After return to the laboratory, extracted samples were analyzed for chlorophyll a and phaeopigments fluorometrically according to the methods of Strickland and Parsons (1968) . 11 RESULTS OaLOROPHYLL VALUES AT MASTER STATIONS Title vertical distribution of chlorophyll a values in mg/m^ corrected for phaeopigments at the master stations sampled in Lake Ontario is given in Figure 2. In May, mid- lake stations 24 and 75 showed relatively low and uniform values throughout the water column. At station 96, however, values were extremely high (17 mg/m^ at 1 and 5 m) in the near-surface water and significantly higher than the other stations at other depths. In June, values were somewhat elevated at station 10, and a much larger surface peak was present at station 24. Stations 45 and 75, which both fell within the "cold core" region during this sampling cruise, had very low and vertically uniform chlorophyll a values. Samples from station 96 taken during this cruise were unfortunately lost due to a laboratory accident. In July, all master stations in the open lake show€id remarkably similar chlorophyll levels and patterns of vertical stratification. Peak values occurred at 10 m depth in all of them, and significant decreases in chlorophyll concentration were noted both above and below this depth. At station 96, in the eastern end of the lake, values were lower at all depths and fairly uniform down to 10 m. There was a very slight peak at 10 m, and values declined below that depth, as they did at the other stations. Corrected chlorophyll a values were surprisingly low in August, particularly at stations 24 and 75. Stations 10 and 45 showed slight peaks at 5 m depth, and values at station 96 were also elevated and more uniform with depth. In October, very low values were present at station 10. Stations 24 and 45 had somewhat higher values and concentrations were fairly uniform' down to 100 m. Surface values at station 75 were similar to those found at the previous two stations, but declined below 20 m and became very low below 30 m. Chlorophyll values at station 96 were comparable to the other stations sampled at the surface and remained at the same levels at all depths sampled. In November, no pronounced vertical trends were evident at the stations sampled and values were quite low, except at station 96 in the eastern end of the lake. In February, chlorophyll values were low and uniform at the open-lake stations sampled. No samples from station 96 were obtained during this cruise. In March, values remained low and relatively uniform at the open-lake stations, but were significantly elevated at station 96, in the eastern end of the lake. In April, values increased but remained relatively constant with depth at the four open-lake stations. Values remained significantly higher, and evidence of vertical stratification was present at station 96. In June, chlorophyll values increased significantly in the upper part of the water column, with peak values occurring within the top 10 m at most of the stations. Station 45 presented a somewhat anomolous case, with peak values occurring at 30 m. 13 MfiT 15-19. 1972 to Ol • ►- to to to 7 300 ' 10 2U ? «15 to 17.2 75 96 JUNE 12-16, 1972 to to e 2U r to to tiS 75 96 JULY 10-14. 1972 to 24 to 96 FIG. 2. Vertical distribution of chlorophyll a at master stations. 14 RUGUST 21-24, 1972 10 to F 10 z: so If aoo 10 to /> 24 45 75 to 96 OCT 30 - NOV 3. 1972 to Oi 1 1— to vu i so to '' 300 y-i 1- 10 10 y 24 45 75 to 96 NOV 27 - DEC 1. 1972 to to to to .«« S> ■ ■ H 1— UJ ■ ' , , i:so. & 1 i ^ < ^ < > ■ 300 10 24 45 I 75 [ 96 FIG. 2 continued 15 10 0, 1 H E SO- o 300 10 FEBRUnRY 5-9. 1973 !0 10 10 V < 214 1 45 75 10 e 96 10 0, 1 1- I— z: iso+l a» ■ 10 MRRCH 19-22. 1973 to 10 to ? < 214 % 45 75 10 } 96 to LlJ O KO ■ 10 APRIL 24-28, 1973 to 211 10 ^ 45 to 75 to i 96 FIG. 2 continued. 16 XLiQ. 200 JUNE 11-14. 1973 10 Oj > ^ ' - 10 to e 75 98 FIG. 2 continued. PARTICLE COUNT DATA Graphic representations, of the areal distribution of particles in the particular size classes measured in the near-surface waters of Lake Ontario are given in Figures 3-7, Representations of verticle distri- bution of particles in the same size classes sampled on each of the biology-chemistry cruises are given in Figures 8-10. For the purposes of this project, particle count data are regarded as relatively crude information, but sufficiently accurate to allow reasonable interpretation of trends between points measured by more accurate but more tedious methods. Since there are obviously particles other than living algae in the seston of Lake Ontario, it cannot be expected that the particle count technique would give an acceptably accurate estimation of the abundance of phytoplankton on a direct basis. Since particle count size classes are directly related to the volume of particular particles sensed fay the device, it might be suspected that a. closer relationship would be found between particle counts as an estimate of phytoplankton abundance and a measure of gross biomass, such as chlorophyll, than to direct counts of phytoplankton, which con- tain species of vastly different physical sizes and states of aggrega- tion. This supposition appears to be supported by the results of our study. When compared with f luorometrically determined chlorophyll values from the master stations (Table 4), reasonably close correlations were found, particularly with the intermediate size classes, in samples from the first two cruises. Although remaining significant statistical- ly, correlation declined during the summer months and tended to increase in the fall. No correlation was found in samples taken during Febru- ary, but they increased again during the early spring sampling period. Correlations for samples and cruises on comparable dates were not as 17 TABLE 4. Correlations between fluorometrically determined chlorophyll a values and particle counts for all depths at master stations. Month P, . C . Channel 5-10 10-20 20-40 40-80 80-150 5-150 R@.99 May .8670 .9467 .9390 .8042 -.0318 .9285 .5256 June .8684 .7806 .2885 .3640 .8092 .8342 .3843 June* .9114 .9297 .8697 .8584 .8130 .9366 .3887 July .7893 ,8638 .6996 .4977 .3749 .8279 .3575 August .5994 .7006 .6806 .6505 .5145 ,6386 .3477 October .6940 .7328 .6863 .5586 .4259 .7134 .3575 November .8317 .9298 .9206 .8704 .3779 .8835 .3932 February .0067 -.3476 -.1164 -.1122 -.2211 -.0695 .3801 March .7434 .9222 .9621 .8872 .1206 .8294 ,4182 April .3159 .5943 .7294 .2793 ,0178 .4930 .3477 April** .3305 .7533 .8843 .6357 .1796 .5514 .3509 June .5647 .7262 .7964 .8708 .7549 .6471 .3646 June*** .5952 .8599 .8060 .8753 .7557 .6986 .3683 ** *** Excluding 1 extreme outlier point apparently resulting from sedi- ment contamination of P.C. sample (station 75, near-bottom sample, 221 m) . Excluding 1 extreme outlier point apparently resulting from contam- ination of P.C. sample (station 45, 150 m sample). Excluding outlier point apparently resulting from P.C. bottle con- tamination (station 75, 1 m sample). strong as they had been the previous year. Correlations are strongly affected by the introduction of single nonrep- resentative samples into the set considered. In the results presented (Table 4) , we have recalculated certain values excluding data from samples which were obviously contaminated with sediment. While certain other data points, particularly in the set from the October cruise, are regarded as suspicious, we have included all cases where source of con- tamination could not be determined beyond reasonable doubt by inspection of the sample. It is apparent that correlation could be improved significantly by the adoption of arbitrary criteria for exclusion of outliers . The anomolous results obtained from the February samples are somewhat confounding. The most immediately plausible explanation would be a systematic error in the chlorophyll results from this month. We have 18 not been successful in detecting any such error. We suspect that the unsatisfactory result may arise from the fact that very low values for particle counts and chlorophyll were present in samples from this cruise and many of the algal populations present were in the larger size class, resulting in relatively poor extraction of the chlorophyll present by the method utilized. This factor also may produce a reduction in observed correlations during the summer months when asseniblages at most stations were dominated by the larger green and blue-green algae. Comparison of the particle count data with spectrometrically determined chlorophyll values furnished by other projects is somewhat less encour- aging (Table 5) , Although highly significant statistically except during February, the correlations between results from the two methods are not what might be expected from methods which purport to measure the same quantity. Correlations are particularly poor in results from the summer cruises, and no correlation was found in the previously noted anomolous February case. Glooschenko et al. (1972) have noted particu- larly high phaeopigment fractions in Lake Ontario waters during the summer months . Although corrected chlorophyll a data were used in both data sets discussed here, part of the apparent non-correspondence between the two methods may result from inconsistencies in arriving at accurate correction for phaeopigments. The correlations between raw cell counts of phytoplankton and spectrometrically determined chlorophyll values are also very poor for the summer cruises. A relatively high correla- tion was found between raw cell counts and spectrometrically determined chlorophyll a values in February, although correlations with other parameters measured were extremely low. Areal Distribution by Size Class Data on the distribution of particles in the surface waters of Lake Ontario are presented in Figures 3-7. In addition to data gathered as part of the principal project, we have included measurements made under the auspices of a complementary project (Intensive Study of Lake-Wide Changes in Spring Phytoplankton and Certain Related Parameters, supported by U.S. Department of Commerce NG-17-7 2) in the interests of tracing the time course of early spring changes with the greatest fidelity. Cruises undertaken as part of the principal project are designated as Main-Lake Biology-Chemistry (BC) and those undertaken as part of the other project are designated as Spring Bloom (SB) cruises. Samples taken on the first SB cruise showed relatively high densities of 5-10 um particles at stations in the Niagara and Toronto vicinities. Over the rest of the lake, densities were moderate at most stations, with pronounced low at several mid-lake stations and slightly elevated at stations nearest shore (Fig. 3A) . Samples taken on the second SB cruise showed slightly reduced densities of particles in this size class at stations near Niagara and Toronto, but increased levels at stations nearest shore in the rest of the lake, particularly along the southern shore (Fig. 3B) . Although the stations near Niagara and 19 TABLE 5. Correlation coefficients for EPA spectrometrically determined chlorophyll a values and: (1) f luorometrically determined chlorophyll a values (master stations only), (2) 10-20 ym particle counts, (3) 20-40 pm particle counts, (4) total cell counts. May June July Aug. Oct. Nov. Feb. March April June (1) .8890 .9765 .8500 .6949 (2), .7171 .5782 .7177 .6194 (3). .5856 .4536 .6094 .5291 (4). .6277 .5213 .3573 -.1409 .8930 missing .0206 .4724 missing .2930 .4703 missing .0195 .1644 missing .7740 9027 .9643 .7103 6474 .5410 .3863 6610 .3941 .3335 8628 .8837 .2835 Toronto were not sampled on the first BC cruise, samples taken at this time showed continued increase in particle densities at nearshore sta- tions along the southern shore (Fig. 3C) . Results from the third SB cruise indicated that this trend continued, with increases beginning at offshore stations in the southeastern part of the lake (Fig. 3D) . A continued spread of relatively high particle densities in the 5-10 ym size class was evident in the results from the fourth (Fig. 3E) and fifth (Fig. 3F) SB cruises, particularly at stations in the eastern and western ends of the lake. By the time of the June 1972 BC cruise, relatively high and uniform particle counts were found at all stations sampled, except for a group of offshore stations in the southern half of the lake (Fig. 3G) . A similar situation was found on the sixth (Fig. 3H) and seventh (Fig. 31) SB cruises, when particle densities were relatively high and unifonn except at station 45 which showed strikingly low values at both sampling periods. Particle densities in this size range were fairly uniform in samples taken during July (Fig. 3 J) and August (Fig. 3K) , although somewhat reduced values were found at stations in the Hamilton-Niagara vicinity during July and the Oswego vicinity during August. Stations sampled during the October BC cruise showed markedly reduced and rather irregular 5-10 ym particle densities (Fig. 3L) . By the time of the November 197 2 BC cruise, particle densities were greatly reduced at all deep-water stations, but remained high or tended to increase at stations near shore and in the shallow northeastern basin (Fig. 3M) . Approximately the same situation was evident during February 1973 (Fig. 3N) , although slightly increased particle densities were noted at a few offshore stations. In March (Fig. 3 0), particle densities remained high at stations nearest the southern shore but were consistently reduced at stations near the north shore. The same trend was visible during the April cruise (Fig. 3P) , with a general reduction in average particle count values. Similar to the previous year, by June 1973 particle count values had become relatively uniform across the lake (Fig. 3Q) except for a couple of strikingly low values at offshore stations and a pronounced high at 20 MfiT 2-5, 1972 Toaarro BOCHESTEH MAT 10-12. 1972 T/3R0NTO BOCHESIEB FIG, .3. Areal distribution of 5-10 ym particles. 21 MAT 15-19, 1972 TOflONlO mr 24-25, 1972 TORONTO 2000CO.OO FIG. 3 continued, 22 MRT 30 - JUNE 2,1972 BIVtB ROCHESTER JUNE 5-7, 1972 TORONTO ROCHES TEa 200000.00 FIG. 3 continued. 23 JUNE 12-16. 1972 Tooofno BlVtS ROCHESTER JUNE 19-22. 1972 TORONTO H FIG. 3 continued. RODCSTER 2ooo:o. 00 24 JUNE 26-28. 1972 TORONTO 200000.00 ROCHESTER TOROrno JULY 10-m, 1972 c^vV fiOCHESIEfl FIG. 3 continued. 25 RUG 21-24, 1972 TORONTO ROCHESTER 2CO0CO.0O K TORONTO OCT 30 - NOV 3. 1972 ROCHESTER FIG. 3 continued, 26 TORONTO NOV 27 - DEC 1. 1972 M 2O0CCO.0O nOCH£5TEa FEB 5-9, 1973 TORONTO 200COO.OO FIG. 3 continued. 27 TORaSTO MRR 19-22. 1973 mv-3 20CCCO.OO ROCHES rE,=i TORONTO flPR 24-28, 1973 2O0«X).0O fiOCHcSTER FIG. 3 continued. 28 JUNE 11-14. 1973 TOfiOWTO soocco.oo ROCHESTER Q FIG. 3 continued. station 12 near Niagara. Samples from the first SB cruise (Fig. 4A) showed relatively high den- sities of 10-20 ]m particles at stations near Niagara and Toronto and at certain stations in the far eastern part of the lake. Over the rest of the lake there was a trend toward higher counts at stations nearer shore, but values were appreciably less than in the Niagara area. A sijnilar situation was found on the second SB cruise (Fig. 4B) ,. although counts at stations nearest shore in the main lake had increased appreciably. Samples from the first BC cruise (Fig. 4C) showed de- creased levels of 10-20 pm particles at nearshore stations along the north shore, but levels remained high along the southern shore, partic- ularly in the Mexico Bay region and in the northeastern basin. Average values decreased somewhat in samples from the third SB cruise (Fig. 4D) and remained relatively stable in samples from the fourth SB cruise (Fig. 4E) although relatively high values had begun to spread to offshore stations. This trend continued, on the basis of results from the fifth SB cruise (Fig. 4F) , and by the time samples from the June BC cruise were taken (Fig, 4G) significantly low values were found only at a group of stations offshore in the southern half of the lake. The area of the lake having water with low particle densities apparently continued to decrease, since such values were noted only at three sta- tions sampled during the sixth SB cruise (Fig. 4H) and at a single station sampled during the final SB cruise in late June (Fig. 41). In 29 MAY 2-5, 1972 lonofno HBaJLTW ROCHESTER MAT 10-12, 1972 TOBONTO nocMEsrER B FIG. 4. Areal distribution of 10-20 ym particles. 30 TORONTO MRT 15-19, 1972 NIXWR mvu eocco.co ROCHESTER MAT 24-25, 1972 TOflONTO eooco.oo FIG. 4 continued. 31 MRY 30 - JUNE 2,1972 TOflONTO ROCHESTER JUNE 5-7, 1972 TORONTO ROCHESTEn FIG. 4 continued. 32 JUNE 12-16. 1972 TORCHTO eoooo.oo RocHEsiea TORO^O JUNE 19-22. 1972 80000.00 ROCHES I £R FIG. 4 continued. 33 JUNE 26-28, 1972 Toflcmo 800CX3.00 ROCHESTER JULY 10-14, 1972 TOaONTO ROCHESTER FIG. 4 continued, 34 RUG 21-24, 1972 TOfiONTO K 1 \ \ nOCHESTEB OCT 30 - NOV 3, 1972 TOROMTO BOCHESIER FIG. 4 continued. 35 NOV 27 - DEC 1, 1972 TORONTO ROCHESTEfl M FEB 5-9, 1973 •lOROwro nOCMESTER N FIG. 4 continued. 36 TOfiCKfO MflR 19-22. 1973 6COO0.OO ROCHESTER RPR 24-28, 1973 TOROmO ROCHES lEH FIG. 4 continued. 37 JUNE 11-14, 1973 TORONTO 60000.00 ROCHESTER FIG. 4 continued, July (Fig. 4J), 10-20 ym particle densities were relatively high and uni- form at most stations sampled throughout the lake, although there was some tendency towards reduction in abundance at stations in the eastern basin and near shore, which had highest values early in the season. Particle count values in this channel remained relatively high and uniform at all stations sampled during the August cruise (Fig. 4K) , although some minor but apparently systematic variations were present. Average values were significantly lower in samples from the October cruise (Fig. 4L) and quite irregular over the lake, although there was some tendency for higher values at stations nearest shore. The latter trend apparently continued, since samples from the November cruise (Fig. 4M) showed significantly higher counts at stations nearest shore and in the far northeastern basin than in the open lake. Counts at nearshore stations decreased somewhat in our February 1973 samples (Fig. 4N) , but substantial increases were noted at most stations along the southern shore in March (Fig. 4 0). Values at these stations decreased somewhat in April (Fig. 4P) but tended to increase slightly at offshore stations and along the northern shore. By June (Fig. 4Q) , relatively high levels were found at most stations across the lake, but there appeared to be a definite south-to-north trend in abundance with highest values being found at nearshore stations in the Rochester and Niagara vicinities. 38 Relatively low levels of 20-40 yxa particles were found at stations sampled during the first SB cruise in early May (Fig. 5A) . Highest levels were noted at stations in the southwestern part of the lake, near Niagara, and in the northeastern island area. Approximately the same situation was evident in samples collected during the second SB cruise (Fig, 5B) , but appreciably increased levels were found at stations nearest shore. Samples from the May BC cruise (Fig. 5C) showed consider- ably increased levels at nearshore stations in the southern part of the lake and in the northeastern Island area, but not at stations along the north shore. Maximum values noted on the previous cruise had declined somewhat by the time samples were taken on the third SB cruise (Fig. 5D) b^lt remained relatively high in the eastern part of the lake. This pattern was changed by the time samples were taken on the fourth SB cruise (Fig, 5E) , and highest values were found at stations near Niagara. A similar situation was found on the basis of samples from the fifth SB cruise (Fig. 5F) , although there was some tendency for higher values to spread to stations farther from shore. By the time of the June BC cruise (Fig. 5G) , highest values were found at a band of stations in the north half of the lake and at stations along the southern shore, with low values along the north shore and at offshore stations in the southern half of the lake. On the sixth SB cruise (Fig. 5H) , lowest values were found in the south central part of the lake, with relatively higher densities in the north and east and particularly in the west end of the lake. Samples from the final SB cruise (Fig. 51) showed highest values in the southwestern part of the lake and an apparent west-east overall trend. In July (Fig. 5J), average values were reduced and densities more variable between stations, as they were in smaller size ranges. In August, average values increased somewhat (Fig. 5K) but there was considerable variation between stations and no outstanding regional patterns. In October (Fig. 5L) , particle densities in this size class were reduced to low and rather uniform levels, but increased at stations in the northeastern Island area, and to a lesser extent at nearshore stations throughout the lake (Fig. 5M) during November. In February (Fig, 5N), values were uniformly low except for a marked high at station 14, near Niagara. Our March samples showed increased values at certain stations along the southern shore (Fig. 5 0), and by April (Fig. 5P) this trend had spread to all nearshore stations and to stations in the northeastern part of the lake. Rather irregular values were found in samples from the June 1973 cruise (Fig, 5Q) , but there appeared to be a north-south trend in abundance, as there was in the smaller size ranges. Samples from the first SB cruise (Fig. 6A) showed relatively high counts of particles in the 40-80 ym channel at stations in the northeast and southwest parts of the lake and at some stations in the north-central region. Results from the second SB cruise showed a slight increase at stations nearest shore on both sides of the lake (Fig. 6B) . Conditions were apparently similar during the time the samples from the May BC cruise were taken (Fig. 6C), with relatively high values at most shallow stations. Results from the third SB cruise (Fig. 6D) indicated a slight decline, except at stations in the east and west ends of the 39 TOROtnO TORONTO MfiT 2-5. 1972 BOCHESIEB MRT 10-12. 1972 BOCHESTEH 20000.00 20000.00 FI6. 5. Area! distribution of 20-40 pm particles. 40 TOBQNTO MAT 15-19. 1972 MCHESTEH TORONTO MAT 24-25. 1972 20000.00 ROCHESrEa FIG. 5 continued, 41 lOROWTO MAY 30 - JUNE 2.1972 ilVEA 20000.00 ROCHESTEa TORONTO JUNE 5-7. 1972 20000.00 ROCHES TEft FIG. 5 continued. 42 JUNE 12-16. 1972 TOBOMTO flOCHESTEH TOBONIQ JUNE 19-22, 1972 UKtrn' Ufa ROCMESItn 20000.00 H FIG. 5 continued. 43 JUNE 26-28. 1972 TORONTO ROCHESTEn TORONTO JULY 10-14, 1972 20000.00 B0CHE3IEB FIG. 5 continued. 44 RUG 21-24, 1972 TORONTO BOCtCSTEB K OCT 30 - NOV 3, 1972 TOBarro FIG. 5 continued, 45 NOV 27 - DEC 1. 1972 TORONTO BOCMESTEfl TORcrno N FIG. 5 continued. FEB 5-9. 1973 BOOCSTEH 20000.00 46 MRR 19-22. 1973 TOBONTO TOfiOtfTO flPR 24-28, 1973 20000.00 nOCMESTEFI FIG. 5 continued. 47 JUNE 11-m. 1973 TORONTO KXMESTea FIG. 5 continued. lake, and the trend toward higher levels at these stations was evident in the results from the fourth SB cruise (Fig.-6E). Levels remained relatively high in the west end of the lake at the time of the fifth SB cruise (Fig. 6F), and increases were noted at some offshore stations. The same pattern evident in counts from the 20-40 ym channel appeared to be present in results from the June BC cruise (Fig. 6G) , with rela- tively high values along the south shore and in the north central part of the lake, and low counts along the north shore and in the south central region. Relatively low counts were present at some offshore stations and a group of stations east of Niagara during the sixth SB sampling period (Fig. 6H) , with relatively high counts at stations Immediately west of Niagara. During the final SB cruise (Fig. 6l) there appeared to be a southwest to northeast trend in values, as there had been in some of the smaller channels. Samples from the July BC cruise (Fig. 6J) showed relatively high and uniform values except for low values at a group of stations in the south cfentral part of the lake and a few stations near Toronto. Values increased appreciably at most stations sampled during August (Fig. 6K), but declined again in October (Fig. 6L) . In November (Fig. 6M) , low values were found at most offshore stations but were uniformly higher at stations nearest shore and considerably higher at stations in the northeastern sector of the lake. Only isolated high counts with no particular pattern were found during February 1972 (Fig. 6N) and March 1973 (Fig. 6 0). In April 48 TORONTO MRT 2-5. 1972 1000.00 KJCtlESTEH TOBONTO ni(caf» MVCR MRT 10-12. 1972 1000.00 BOCHESTEn FIG. 6. Areal distribution of 40-80 ym particles. 49 MAY 15-19. 1972 TORONTO ROCHESTER TORONTO MRY 24-25, 1972 BOCHESTEB 1000.00 FIG. 6 continued. 50 MAT 30 - JUNE 2.1972 TORONTO TORONTO JUNE 5-7. 1972 1000.00 nOCHESTER FIG. 6 continued, 51 JUNE 12-16. 1972 TOROKTO ROCHESTER JUNE 19-22. 1972 TOBOKTO BOCftSTER H FIG. 6 continued. 1000.00 52 JUNE 26-28. 1972 TORa'no 1000.00 BOOiESTEB JULY 10-14. 1972 TORONTO FIG. 6 continued. 53 RUG 21-24. 1972 TORONTO tooo.oo ROCHESTEa TORONTO OCT 30 - NOV 3. 1972 ROCtCSTEB FIG. 6 continued. 54 TORONTO mctm iiivni NOV 27 - DEC 1. 1972 BOOCSTER M TDROKIO FEB 5-9. 1973 N BOCHCSTER 1000.00 FIG. 6 continued. 55 MRR 19-22. 1973 TORONTO RPR 24-28. 1973 TORONTO BOCMESTEH FIG. 6 continued. 56 JUNE 11-14. 1973 TOBOrnO lOOO.OO HtPCffO mvct ROCMESTEB FIG. 6 continued, (Fig. 6P)j however, there was a definite pattern of higher occurrences at stations nearest shore and in the eastern island area. In June (Fig, 6Q) , highest values were found along the southern shore and in the north central part of the lake, as was the case in some of the smaller channels. Particle counts in the 80-150 ym size channel were relatively low in samples from the first two SB cruises (Fig. 7A,B),' and only slight Increases were noted at stations near shore and in the eastern part of the lake during the May BC cruise (Fig. 7C). Continued slight increases were noted at stations in the eastern part of the lake and stations near Niagara on the three following SB cruises (Fig. 7D, E, F) . Samples from the June BC cruise showed scattered very high values at stations along the southern shore and in the eastern part of the lake (Fig. 7G) . Samples from the two following SB cruises (Fig. 7H, I) showed a tendency towards decrease at stations in the eastern part of the lake and increase at stations in the west. In July (Fig. 7J), however, values in this size range were very high at stations along the southern and' eastern shores and relatively low at stations in the western part of the lake. By August, overall average values had declined (Fig. 7K) and striking declines were evident at stations that had been high the previous month. High values were present at a series of stations in the 57 MAY 2-5. 1972 TORONTO ROQCSTEfl MRY 10-12. 1972 TORCWTO FIG. 7. Areal distribution of 80-150 ym particles. 58 TORCNTO HIKfFH wvra m't 15-19. 1972 ROCHESTER MRY 24-25, 1972 TOROMO ROCHESIEfl FIG. 7 continued. 59 MAY 30 - JUNE 2,1972 TORONTO ROCHESTER JUNE 5-7, 1972 TORomo ROCHESTEfl FIG. 7 continued, 60 JUNE 12-16. 1972 TOROKTO ROCHESTEB JUNE 19-22. 1972 TORono FIG. 7 continued. 61 JUNE 26-28. 1972 TOROMTO JULY 10-14, 1972 TORono FIG. 7 continued. 62 AUG 21-24, 1972 TOROMTO ROCHESTEft OCT 30 - NOV 3. 1972 TORONTO ROCHESIEfl FIG. 7 continued. 63 TOROMTO FEB 5-9. 1973 nOOCSTER M TORONTO NOV 27 - DEC 1. 1972 N noocsTEn FIG. 7 continued. 64 MflR 19-22. 1973 TIWJNTO RPR 24-28, 1973 TORONTO lOOtSTER FIG. 7 continued. 65 JUNE U-lil. 1973 TORCWTO ftOCHESTEft FIG. 7 continued. Hamilton-Niagara region. Particle densities in this size range declined drastically by October (Fig. 7L) and remained -low during the \d.nter and spring (Fig. 7M, N, 0, P) . A substantial increase was noted in June samples (Fig. 7Q) , but levels approaching those common the previous year were present only at a single station in Mexico Bay. Vevtiaal Distribution by Size Class The vertical distribution of 5-10 ym particles at stations sampled on the main lake biology-chemistry cruises is plotted in Figure 8. Stations sampled during May showed relatively little vertical stratification, although samples from stations 42, 72, 73, 59, 79, and 90 showed a definite vertical trend in abundance. Stations sampled during June 1972 showed more or less pronounced vertical stratification, except stations 26, 32, 40, 44, 62 and 75 which had very low counts and no apparent vertical trend. Similar vertical distribution was noted at stations 15, 45, 46 and 54 but particle densities at these stations were somewhat higher. Very similar patterns, possibly indicative of regional water mass similarities, were noted at stations 30 and 31 and at stations 52, 64, and 66. All stations sampled during July showed some evidence of vertical stratifi- cation, and some apparent regional patterns were evident. At stations 5, 10, 24, and 26, 5-10 ym particles were appreciably concentrated at 66 10 m while at stations 38, 40, 44, and 45 there appeared to be a distinct biceak in concentration levels at the 20 bi depth. Somewhat surprisingly, samples taken during August did not show as distinct -vertical patterns as the samples from previous months, perhaps as a result of a f lor is tic shift of species in the larger size classes, At this time similar patterns were noted at stations 45 and 46, although adjacent station 44 was strikingly different. Stations 62, 64 and 69 showed a different But internally consistent pattern. Stratification of particles in this size class apparently broke down in October and, as would be expected, no trends were evident in the winter and early spring samples. In April, anomolous results were obtained at station 26. Samples from the June 1973 cruise showed an unusual pattern at the same station when particle densities that were down to 40 m then increased. A similar pattern was found at station 44. Apparently similar vertical distribu- tions were found at stations 46, 62, 64, and 66, but results from this sampling period were, in general, much more irregular than in the same month the previous year. Vertical distributions of 10-20 and 20-40 ym particles are plotted in Figure 9. May samples showed significant stratification of particles in these size categories at stations 30, 31, 72, and 73 along the south shore, stations 94, 96, 97, and 98 in the eastern island area, and station 105 in Mexico Bay. Other stations sampled showed little signi- ficant stratification. Stratification of particles in these size ranges MAT 15-19, 1972 FIG. 8. Vertical distribution of 5-10 ym particles. 67 MAY 15-19, 1972 t Toeoog MDDM jceooe wootc tooom moom 2sooao tomm mmm tmmo a. ' :l 36 38 ? tiO II 42 e 44 45 46 48 49 S ' ^ 2«e f f( 52 H ( J 1 1 J 1 1~ 54 56 59 60 62 64 ^ 66 67 69 MRT 15-19. 1972 ' . "'"' . "OOtW . »000 ?00000 FIG. 8 continued. 70 JULY 10-14. 1972 « 3«0OM 2M«M . 200000 . TOOOM . iMMO . aOOMO MOOllO , »0000 MOOOO MOpOO JULY 10-m. 1972 rirFFFP* too 90 92 m 95 96 97 98 99 103 105 FIG. 8 continued. 71 nUGUST 21-24. 1972 wxKm tooom socooo atxwoo aaeco iocoon fiUGUST 21-24, 1972 MOOOC MOOO* 200043 JOOOOS 200500 200000 200000 200000 200000 200000 <\ ru~ 46 ^ 48 ■49 f7~rT 7* 66 67 69 FIG. 8 continued. 72 RUGUST 21-24. 1972 e . MflOM . MMoa . MMW . aooM« aoowo . ?waae swom 2mmo ismm mmm g : SO" aos <> T^fT* r 4—1 I 1 I I 71 72 73 75 77 78 79 \ 83 85 89 •f7 aoo e 90 92 91 95 96 97 98 99 103 105 « 2000M »r-r* — >- S rr Hi OCT 30 - NOV 3. 1972 aiopoo ioopoo . 200000 200000 200000 200000 7 el rr e\ 200000 H— 200000 200000 7T 10 12 i\ m 15 6 dbso s ■ MO rrn 17 19 i 20 2U 26 30 31 }\ 32 31 35 FIG. 8 continued. 73 OCT 30 - NOV 3, 1972 « iOMM 100090 3000119 200000 »!000« VSOOOO 200909 200000 ■ ■ « -J I 4 1 — I — r-« 1 — r-T — > * g i 2M0O0 IO0004 v i I — • : — r-+- — • — . seal 36 1 36 40 11 i 42 _[ m A 45 1 US 48 119 ^50i -I 1 — _ — I I SM 52 ; 51 i 56 59 < ::^ 60 r 62 61 66 67 89 OCT 30 - NOV 3. 1972 6 iOOCOO ZCOOOO 7000O0 30M0I3 20000« 200OO0 200000 200000 200004 200000 '{["f i s« ~4 1 t J—* 1- 71 72 73 U 75 ? i 200 90 92 94 77 78 ■ ^\ 79 83 85 89 -1 1 ( — r* ^ fT 95 1 96 97 98 99 i 103 105 FIG. 8 continued. 74 NOV 27 - DEC 1. 1972 r^ ii\ 17 19 20 ^ 24 26 30 31 A 32 31 35 NOV 27 - DEC 1. 1972 t 200000 iOOOOO 300000 TOiOtC 200000 200000 200000 200000 200000 200000 fl[ > I . 1 > I — l i I ■< — I ' 1 ' — I < i I — I II [ . I 1—- [ I 1-- • • — ■ • — 36 38 40 41 42 44 45 45 .. 48 49 g ■ If 30}.. ^ 52 54 56 59 60 62 ::1 64 65 67 69 FIG. 8 continued. 75 NOV 27 - DEC 1. 1972 a iooooe 200000 3«00fl 300000 SWOOO 300008 300000 300000 3M ' 71 e 72 i 73 4 (— I— — • 1 I f » I ? ^ 3OO0M ?00000 ?06d00 75 77 78 79 83 85 89 g iOO 90 92 94 95 96 97 98 SQ 103 ,. 105 FEBRURRT 5-9. 1973 300000 300000 300000 300000 300000 300000 300000 300000 300000 300000 gi I — pi — I — ) I — J — > 1 I — J II — J — I y I — j — I— J — I— • |-j — I — I — J — ^ — I— !■ I j i — f — I t ■ : 9«" V» 10 12 lU 15 r 17 19 20 24 28 ? 30 31 32 34 35 FIG. 8 continued. 76 FEBRUnRY 5-9, 1973 200000 2CO0OO 300400 200000 SOCOOO 200000 200000 200000 200000 200000 t%-—t 1 — I 1 1— I < 1 — I ' ' — I 1 "t— n — ' 1 — r :i ►— i ■ i 1 — i > — r-i — i ' 1 — -— ^ P-P, . 36 38 40 41 42 44 45 e 46 48 49 a . !i! ■■ e 52 54 56 i> 59 60 r ■J 62 64 66 67 69 FEBRURRY 5-9. 1973 « 200000 8? .. A so ■ 300 ' 71 72 73 75 \ 77 78 79 83 2OOO00 200000 ~t ( I l-r ( 85 89 LiJ 300 T 90 92 94 95 96 97 98 99 103 105 FIG. 8 continued. 77 HRRCH 19-22. 1973 200000 300000 700000 ify)O0O 200000 200000 ?00000 ?00000 200000 200000 ij — f — j__. — __4 — pi — ^ — I — , — — , — , — f — - H — t — ( — *~T~* — n — ' — * — f — ' — r* — f — ' — *v* ' — ' — "" :\ 10 e e 12 ^ 14 15 «i ' ^- £ 17 19 20 p-^ 24 "" — 7 26 30 3! 32 > 34 35 MnRCH 19-22. 1973 200000 0, 1 1 — y T 200000 _| 4 200000 300000 200000 200000 -♦ ( — I 1 *~ 36 } } 38 40 ^ ^ 41 42 44 45 46 48 49 s r. ±504 o. UJ a 52 ^ ^ } 0. 1 fr__ . 1 ( J 1 1 ( , 1 hp- r-j 1 ( j 1 1 f 1— *- 54 56 59 ::i 60 62 <> i — [ 1 1- 64 66 67 69 FIG. 8 continued. 78 MRRCH 19-22. 1973 • M««M 2M9M MOOOO i MOOM MOOM MMM MMM 200«M 2«00O0 2000M s Ml "7 f 30W MO 71 72 73 75 77 78 79 83 85 69 ^ frr i 100 90 92 94 95 96 97 98 99 103 . 105 APRIL 24-28. 1973 • sooooe . iooeoo . Maooo jooooo xaeoo sooooo aooooo iooooa »oom 200000 tl j' *— I 1 ' * I < *— - I »— • I 1 1 ■ pr » I M 1 1 . ■ I 1 . ) t , 1 1 FIG. 8 continued. 79 RPRIL 24-28. 1973 t MOOM VOOOO MOOM 200040 MOOOO 3MM0 700000 TMOOO 200000 MOOOO (f— <— -H 1 1 I I I I I 11 I > | t ■ 11 t I r-. 1 f »i I I j 1 ' ' I . II. M" 36 e 38 40 m 42 14 45 \ 46 48 49 ji I I j — I — t— I — I I I — I I I I I — < t I ■ I > I I I ± 50 • aoo 52 54 56 59 60 62 64 66 67 69 APRIL 24-28. 1973 « 300000 300000 200000 20M00 200000 200000 300000 200000 200000 200000 isoi MO e 71 72 73 T 75 77 78 79 I 83 85 69 0|— ♦— »— I — rl ► 5 sbso I I n I ' n 1 I r-t — I 1 I I I I t ■ I 1 H ► K < < ' i i < < < St I IT T I MO 90 92 94 95 96 97 98 99 103 105 FIG. 8 continued. 80 JUNE 11-14, 1973 « SOOOM «| ' »■ 200000 200000 200000 200000 200000 200000 200000 T IMS ~^vr^ 10 12 lU 15 JUNE 11-m. 1973 e 200000 3MO0O 200000 200000 200000 200000 200CW 200000 200000 200000 r~ ^ SO' I I aW" 36 38 Tvr 10 m 12 11 / 15 ^ 16 18 19 5 52 51 T 7 56 59 60 r F ? 1 62 61 66 67 69 FIG. 8 continued, 81 JUNE 11-14. 1973 FIG. 8 continued, was rather poorly developed at stations sampled during the June 1972 cruise, and significant vertical differences were mostly restricted to stations near shore and in the eastern part of the lake. Samples taken from station 75 during this cruise showed unusually high particle count values in the near-bottom waters. Many stations sampled during July had highest particle count values and significant peaks in particle density at depths ranging from 10 to 20 m, and' particle densities were higher in the upper water column at most stations sampled . An apprecia- ble secondary peak was noted at 50 m at station 56. Samples taken auring August all showed higher concentrations of particles in this size category in the epilimnion, and there was an extreme peak at 15 m at station 40. Certain stations showed relatively high concentrations in the near-bottom waters. Concentration of particles in these size categories was relatively low in samples taken during October, and most stations had relatively insignificant vertical differences. Station 15 was an exception in that vertical stratification in particle density appeared still to be present. Samples from the November cruise showed unusually high particle densities in the near-bottom waters at stations 30 and 31. Samples taken during this cruise from many of the stations in the eastern part of the lake were unusual in that the ratio between abundance of 10-20 and 20-40 um particles was reversed from the normal case throughout the rest of the year. In February and March, however, concentration of 10-20 pm particles exceeded the average ratio. In 82 April, samples froi? station 26 had yery unusual values, as they did in the lower particle count channel, and unusually higk near-bottoBj values were found at stations 45, 46, and 48, In June 1973, particle count values were higher in the top 20 meters, although more variation was present than had been the case the previous year. Station 26 had unusually high values in the deep-water samples, and surrounding stations had extreme peaks at 20 m (sta, 17) and 40 m (s ta, 15 and 32) . Samples taken during the May 1972 cruise (Fig, 10) showed near-surface concentrations of particles in the 40-80 and 80-150 ym size classes at stations 94, 96, and 97 in the eastern end of the lake and station 105 in Mexico Bay. Mid-lake stations 17, 34 and 46 showed relatively high subsurface values in the 10-30 m range. In June 1972, most stations sampled showed stratification of particles in these size classes, with highest values occurring near the surface. There were, however, a series of about 14 stations in the south central "cold core" region of the lake where counts were appreciably lower and stratification was not highly developed. Stations sampled during July all showed stratification near the surface but no particular regional trends were evident. In August, values remained relatively high, with greatest concentrations near the MAT 15-19. 1972 u-.-:«.l u-;-jC.» ir>x.> i»:^.» iK^.t i^xw.i it;jo.» 1M?5.» io:m.» ic-^so.e FIG. 9. Vertical distribution of 10-20 ym and 20-40 ym particles. The 10-20 ym channel is represented by the solid line and the upper scale, the 20-40 ym channel by the dashed line and the lower scale. A star indicates that an entire profile is above the maximum scale value. 83 HRT 15-19, 1972 t[foc.« \K eatw.t c»M.» emoe.s u>cm.i CKoo.i c:«>c.» eoooo.t eocx.» cscm t 1 — « — . — I — ^J — 1 — , — J—-, — , — , — ^ — , — , — — , — , — , — •' i!-;x.« i:oM.e ic^-x.e \Kx.t it wc.o \koo.» i:o:-;.» ' FIG. 9 continued. 84 JUNE 12-16, 1972 t (0000.0 00000.0 10000.0 (0000.0 (0000.0 aOOOO.O (0000.0 t.O (0000.0 ■0000.0 (0000.0 JUNE 12-16. 1972 •0000.0 ftlOOO.O (OOOO.O (0000.0 ^.,v :a tOOOO.O t0000.0 10000.0 10000.0 10000.0 10000.0 lOOCO.O 10000.0 10000.0 10000.0 FIG. 9 continued. 85 JUNE 12-16. 1972 W900.O noooo.o aooco.B goom.s . * . I I - c — • *■ . 'OVX.t ecCKM.B KOtK.t tO00«.e MCM,» COgui.a n — * — ' — • r-y* — *— » — [xt* — 1 — ►— r— ^-^ — • — ♦— > * ■< — » — , . ■ t 1- * lOCOO.S IDOOCO 10090.0 lODOO.O IBWO.O IDODO.O lOOM.S >00D«.O tOOOQ.O JULY 10-14. 1972 tOOM IMM FIG. 9 continued, 86 JULY 10-14. 1972 tCOM tOSM 1«4M tOOM ia«M F JULY 10-14. 1972 _tOMt CdOM ««oe« rrff 79 -4 ►- 63 -I — ►- 1/ '• 85 I I 69 -H 1— i" Mf 90 9i| lOOM lOOM I4«M 95 -* — ►- < ^ ir^ur 9S 97 98 IMM __ I . , . L_^__» 99 103 105 l«M9 -I 1— I , ►_ IMM MOM FIG. 9 continued. 87 RUGUST 21-24, 1972 80000 ttOOOO !) T T I I ni i( ♦r-< — I — ►-tt' — •- UOOe C0(M4 5 7 10 12 m 15 fp^ rv"^ rr^ fT"*^ n?^^^^ rt::?:^ r rr rrr 32 34 35 * IMM 103M two* tMM lOOM RUGUST 21-24, 1972 SMM UDM tstoo coora esoM C9000 cosas eoooo eooM u:m iCiiM IISW tOCM FIG. 9 continued. 88 RUGUST 21-2ii. 1972 VMM MOW ■ 'FT'IT'F'F^P 90 92 • IMM 9U 95 96 97 98 TW 99 103 . 105 IMM IMM IMM tOOM lOMO teOM ( .«M» OCT 30 - NOV 3. 1972 § Mff ftr-r MOW VOMO t j I I — , 1 . » I — >- •MM WMIO C^f^-P* •MM 1/ ' ' - •MM (ONS ^ If 10 12 m I ■! " 1 •■ 15 It I — I u I I 1 ,1 ' * t Ml 17 19 20 24 _) »_ I 1— 4- 26 30 31 1 32 > 31 35 l«M« IMM IMM IMM IMM IMM IMM IMM IMM lOOM FIG. 9 continued. 89 OCT 30 - NOV 3, 1972 KXNM UOM SOSM «eM« WDM COSM * IMM lOOM t««M MOM tlWM IMM tMM ItOtI lOtOO tMM OCT 30 - NOV 3. 1972 ( «M«« tOOM «aO«S CO«M MOM RMM «0M4 CSOM 60M« H ,1 I I I rr-* — ' — ► 71 72 73 75 77 I I 78 -I — »— ?\ ' " < - * ' r i •*" " * — ^ 79 83 85 89 ■n+-H — »- 1 rr ■H 1 >— -I 1 , 1 II I ■ I I I fTR 90 92 914 95 96 4 ►_— ' I I ' ►— I <— ( 1—— ' I I ' 1—4 I 1 1 I 1 »■ 97 96 99 103 105 ( IMM tMM lOOM tMM t«SM lOOM IMM tOM« tM4« FIG. 9 continued. 90 NOV 27 - DEC 1. 1972 tMOO taMO ta«N IHM IMOt ttOOO MMO IMM t««»9 NOV 27 - DEC 1. 1972 lOOM FIG. 9 continued. 91 NOV 27 - DEC 1, 1972 t (MM «MM «44M WOM «MM «MM 2H 71 72 73 75 T^n 77 78 79 , 1 II 1 11 " I I I — I II I t I 1 63 I t 65 eg I I ' I I k» 90 92 * INN lOOM 911 I t 95 96 I s vr ^ ♦— I — »-rt- J iT 97 98 IMM IO«M IMM IMM 99 t I 103 . 105 t««M iOOM FEBRURRT 5-9, 1973 t tSNO W«M tmwo <00M tOOM «00M g < 1 ( I II H- I I I » I I I .1 ■H 1~ ' I ♦ \[ •0000 40000 . * 10 12 111 15 § :H ' 17 19 20 I i l i l I — I 1^1 It — pr« — I — I — 1 ^ t I I K \ < ^ 211 26 30 < 31 rr 32 34 35 * tOOOO tOOOO 10000 tOOOO tOOOO lOOOO lOOOO 10000 toooo toooo FIG. 9 continued. 92 I «SflM WMO FEBRUnRY 5-9, 1973 MOM «M ry 36 36 40 111 I ' * » ' Bl ' ' ► I 12 4>4 .' 15 MW« 46 48 49 ^ iM M« 52 T*-r 54 56 INM IMM UNWO 59 -• — t- §111111 60 J 62 MOM ION« 64 I I 66 67 69 INM tOOM 1«0M FEBRUnRY 5-9, 1973 ( teoM MOM ceoN mom * l»M« l««M lOMS tOMO lOOM l«M» IMM IMM lOOM lOMO FIG. 9 continued. 93 MRRCH 19-22. 1973 ( W«M WWM « n ' } ' fT : St" aof •04M ««0M « — I t - |— I — I — ►— (HUM eooM •OOM «00W I 62 64 66 67 69 * tNN ISOOO tOOM IMM lUM MOM IMM UWN tOOM t«OM RPRIL 24-28,. 1973 f^WMO eooM 600M esooo vm» «mm wsm «m«o vom i MO I I I I | i V « ' ( 71 72 _, — t—. 1 — ,_t 73 ■}) 75 I I ' I t • ; 77 .78 > I \ ^' 79 ., 83 ■H 1 ' 1 y tOOM _l — H_ I 1 1 65 69 g ? T-^ 90 92 94 95 96 97 98 99 103 105 10000 10000 lopoo toooo lOMO ioooo 10000 toooo toooo toooo FIG. 9 continued. 96 JUNE 11-14. 1973 • tMM tOOM lOOM tOOM t«OM tOOM 10000 tOOOO tOOOO lOOOO JUNE 11-m, 1973 «0000 MOOO «MO0 * Moot 10000 10000 tOOOO 10000 tOOOO 10000 toooo toooo toooo FIG. 9 continued. 97 JUNE 11-14. 1973 • WDM «00«« m» MM« MWB .WOW .WOW . WOOB .«flOO» tWOOO K < i i 8 1 *rr^r § ^. t I — I — fc— I — I — I — fyi — I — nr* — •""* — [ I <^ ' ' — I — ' — I — *— I — > — ' — ^~ r—* — ' — ^ 90 92 9^ 95 96 97 96 99 103 105 * usot 10000 toooo 10000 toooo loooo toooo 10000 loooo loooo FIG. 9 continued. surface except at station 40, where a large peaik was noted at 15 m and station 59 where values were very high in the near-bottom sample. In October, values were reduced and stratification was less pronounced at all stations sampled. Subsurface peaks were noted at station 30 (near bottom), station 94 (20 m) and station 99 (5 and 10 m) . As might be expected, samples taken during November 1972 showed relatively little vertical stratification. Very high near-bottom values were noted at stations 26, 30, 31, 32, 34, 36, and 38. Similar to some of the other channels, there was. an evident change in channel ratios at all depths sampled at station 49 and stations 94-99 and 103 in the far eastern area of the lake. Stations collected during February 1973 had relatively low values, although samples from the upper 20 m were significantly higher at station 24, and 5 m peaks were noted at stations 20 and 26. Mid-depth peaks were noted at stations 45, 46, 75, and 89. In March, values were relatively low except at stations 12, 30, and 42 along the southeastern shore and stations 89, 92, and 95-97 in the eastern portion of the lake. Samples from the April cruise showed extreme near-bottom values at stations 45, 46, and 48 and relatively high values at stations 95-98 in the far northeastern end of the lake. High and rather variable values were found at most stations sampled during June 1973, with apparent vertical stratification being present except at stations 32, 44, and 45 where particle counts were low and there was little evidence of vertical 98 stratification. Mid-depth peaks were noted at stations 17 and 77. MRY 15-19. 1972 MRY 15-19, 1972 FIG. 10. Vertical distribution of 40-80 pm and 80-150 pm particles. The 40-80 pm channel is represented by the solid line and the upper scale, the 80-150 ym channel by the dashed line and the lower scale. A star in- dicates that an entire profile is above the maximum scale value. 99 Mnr 15-19, 1972 JUNE 12-16. 1972 «M «M ««« FIG. 10 continued. 100 JUNE 12-16. 1972 JUNE 12-16, 1972 FIG. 10 continued. 101 JULY 10-14. 1972 T ^ Iw yr aoo e i . . 2> ^ 5 -* ! »— ^ * ■ ■■■■* ^— I — *— < »— 1- ■* t" * . r JULY 10-lH. 1972 •00 WO «M NO ■00 «00 (00 «0R •00 FIG. 10 continued. 102 JULY 10-14. 1972 P-te: 1 ' , ' ^ ' - I ' t ' — 1 .». I I ■ I -J . ' » ■ I ' ■ k ' ■ III! — I « ' 1091 4li 9tl 95 96 97 I I — »- 98 " 4 ■■■» ■'■■*■■ 99 103 ., 105 AUGUST 21-24. 1972 yf-- Fig. 10 continued. 103 RUGUST 21-24, 1972 AUGUST 21-24, 1972 ^ I I i ,. 90 » » I 92 ■^■■■■■t- ■■*■ 94 I t » 95 96 t I » 97 -• 1 1 98 < I I i 99 . 103 105 I I I FIG. 10 continued. 107 FEBRURRT 5-9. 1973 r FEBRURRT 5-9. 1973 MO «M FIG. 10 continued. 108 FEBRURRY 5-9. 1973 MRRCH 19-22, 1973 «e § too -I — I — I — I I » t > wo MO 000 too > I » < — I ■ I I -• 1 K— | i I I *■ ft MO (00 WO ] 8 I « I 10 I I I ■ 12 -I — »— »- lU t I I 15 £ SO' 000' r 17 19 I I I ? 20 I I I 4 1 — I '■ r ■ : 2« 26 I t t 30 31 « I I 32 34 35 FIG. 10 continued, 109 MRRCH 19-22. 1973 m «M HI ^ > CK" ^ , 4 "— *• 4 — . ■■ ». i.» ..» •00 «00 ■ »„ ., „ ♦., „- » — . __-» — »__+, 36 38 UO 111 12 w i US m t r ' * ' g <• ...f >■ ■.■♦.■■ I f— I 1 ' f »— -*- ' 4 ■'■4 " 4 — fc ' '♦ " ■ i^' " 4' " ' } U8 1 U9 -t--l ( — *— « » — ■» ■ 52 51 58 59 60 ^ 62 6U 66 67 69 ,»..,. „ ».^^ — . < I i t ' ill ♦ . ^ — ♦■' '4 ♦ ■ - * " - " »■ - 4 — 4' " * * I I ' « ■ ^ - 4. ■4- < ■■ I I ■4- » — *- " -4 ' » ■■t " - * ^ m— ».,..i »,.,- I, .^ -,.^. ■■■», , • ■otowioMwwtoveco MRRCH 19-22. 1973 FIG. 10 continued. 110 RPRIL 24-28, 1973 •00 -4 4 « «00 > * — I — wo -I — » I (M Jr— »- -t 1 1 — ' 1 1 •- 4 1 — . , I « 1~ <• -4 »— 4 too ■» — I — I — e 10 12 m 15 17 I ? -H » ( f, 1 1 k- iri 19 20 ^^ ^ 26 30 i 31 ^ 32 314 35 4. - - 4-' - ft L ..,.^.^ »--» ■ I I 1^ .« . U , > ...I 1_ I ..■■», — 4.. ..-4 — . *- — ■♦■ - .,».■.-,« *-«•-♦■■ -»■ - *- — » ■< >— ^' ^ '* ■' * * ■ ' ¥--' * — » ■■— RPRIL 24-28. 1973 FIG.. 10 continued. Ill RPRIL 211-28. 1973 JUNE 11-lU. 1973 FIG. 10 continued. 112 JUNE 11-lU. 1973 ■ JUNE ll-m, 1973 8 ■ ^■y e '-- A nrrr BM 90 92 * — I — I — • — I— — * — I — e 91 95 e -^^^. 96 97 98 99 i 103 -• » •- 105 » I — I- FIG. 10 continued. 113 PHYTOPLANKTON DATA Aveal Distribution of Total Phytoplankton in Near-surface Waters Trends in total phytoplankton abundance in the surface waters of Lake Ontario are summarized in Figure 11. Based on samples taken during the May 1972 cruise, there appeared to be a nearshore bloom with largest standing crops occurring at relatively shallow stations nearest shore and in the eastern part of the lake. Highest values were found at stations on the southeastern shore, especially near Sodus Bay and in Mexico Bay, although nearly comparable values were found at some stations in the northeastern island area. By the time the June 1972 samples were taken, high phytoplankton standing crop levels had become more generally distributed in the lake and highest abundance values were found at stations in the northwestern sector. Some reduction in abundance was noted at stations on the southern shore which had highest levels the previous month. There was also an apparently consistent trend toward low total phytoplankton abundance at a series of stations offshore in the south central part of the lake. In July, average phytoplankton cell counts were reduced, but there was a tendency for highest values to be found at stations in the southern half of the lake. One particularly high abundance value was noted at station 14, near Niagara. A slight further reduction in total cell abundance was noted in the August samples, and highest values were found at stations in the southern and eastern sectors of the lake. In this respect the situation this month was somewhat similar to that found in early spring, although the tendency towards extremely high values at stations nearest shore was not nearly as pronounced. A continued reduction in total phytoplankton abundance was found in the October samples, and this month no pronounced regional distri- bution patterns were evident although peak values were generally found at mid-lake stations. Total phytoplankton abundance apparently con- tinued to decline in November and although highest values were still found in the offshore waters, relatively small differences were present between the stations sampled. Lowest total abundance found during our study occurred in the February samples. At this time very low phytoplank- ton standing crop was present at most stations sampled, with only signif- icant highs at 79, 96, and 97, near Prince Edward Point. The apparent initiation of the spring bloom is evident from samples collected during March. Highest phytoplankton cell counts are restricted to stations nearest shore, except for those stations in the shallow northeastern part of the lake where values comparable to those found at stations nearest shore in the main part of the lake were found. This trend apparently continued as, by the time the April samples were taken, all stations 114 nnr 15-19. 1972 lOROffTO ROCHESTER JUNE 12-16, 1972 nOOiESTEB FIG. 11. Areal distribution of total cell counts. 115 JULY 10-14, 1972 toBomo ROCHESIER RUGUST 21-24, 1972 Toratno ROOCSIER FIG. 11 continued. 1.16 OCT 30 - NOV 3. 1972 TOBOKTO roCHESTER TOBOtnO NOV 27 - DEC 1. 1972 Nvtn roctcsTER FIG. 11 continued. 117 10B0KT0 10RQKT0 WPOTS' (UVW (UVOI FEBRURRT 5-9, 1973 «3QCST£R HBRCH 19-22. 1973 fSJQCSTER 6000.00 6000.00 FIG. 11 continued. 118 APRIL 24-28, 1973 lOfiONTCI roOCSTEB JUNE 11-14. 1973 TORONTO roooTEB FIG. 11 continued. 119 nearest shore In the main body of the lake and stations north and east of a line between Prince Edward Point and Stoney Point had notably Increased total phytoplankton counts. Increases were also noted at several stations in the open lake and^ as in the previous spring, there was a tendency towards higher values in the northern half of the lake. By June 1973, high phytoplankton abundance was present at most stations throughout the lake. In general, levels of abundance were greater at offshore stations than they were at stations nearest shore, although notably low assemblage abundance was found at stations 15 and 44 and there appeared to be a consistent pattern of relatively low values at stations in the north central portion of the lake. Areal Distribution of Major Groups in Near-surface Waters Seasonal trends in the abundance of major phytoplankton groups in the surface waters of Lake Ontario, averaged for all stations sampled during any particular cruise, are shown in Figure 12, Several interest- ing points are evident in this summary information. The first is that the gross composition appeared to be quite different during the two spring periods sampled. In 1972, diatoms were dominant during the spring and early summer, with secondary contributions by green algae, mostly Soenedesmus bioellularis ^ and microflagellates. In 1973, however, although diatoms were again dominant in the early spring, the microflagellates became dominant by June and their average abundance on a cell count basis was more than twice as high as it had been the previous year. Although the trends shown may be partially an artifact of sampling periodicity, our evidence suggests that there were con- siderable differences in major group composition of the phytoplankton community in the two years. The same trend is apparent in the seasonal trends of the green algae. In 1972 there was a strong peak, apparently caused by the unusual abundance of a single population, and a secondary peak in late summer which was contributed to by a number of species. No similar spring peak in abundance of green algae was detected in our 1973 samples. Our results also indicate that the peak abundance of blue-green algae occurred unusually late in the season in 1972. This component of the phytoplankton community reached its greatest abundance in October with a nearly syrataetrical increase and decline on either side of the peak. Previous studies on phytoplankton periodicity in Lake Ontario (Munawar and Nauwerck 1971) have indicated that a late fall peak in abundance of blue-green algae is not uncommon. On the basis of the same study, it would appear that the relative abundance of major groups found in 1973 may be the more typical case for Lake Ontario, since they emphasize the importance of several species of microflagellates in their collections. On the other hand they report that Soenedesmus was a spring dominant, as it was in our 1972 collections but not in 1973. Thus the situation is not entirely clear, and it is highly probable that in a system as highly disturbed as Lake Ontario there is no consistent yearly pattern of phytoplankton succession and the 120 1400- 1000- a 800- CO m o 600- 400- 200- / » Bac illar lophy ta Chlorophyta Cyanophyta Mlcroflagellates A MY JN JL AG DC NV FB MR AP JN FI<;, 12. Seasonal average abundance of major phytoplankton group cell counts. events of a particular year are largely determined by yearly variations in climatic conditions, as they appear to be in western Lake Erie (Chandler 1942). The fraction of total surface plankton contributed by the major groups is summarized in Figure 13. It was necessary to scale the figures for different months in order to accommodate the variation in assemblage density found at the different sampling periods. In our May 1972 samples diatoms were dominant at most nearshore stations in the southeastern part of the lake. Mlcroflagellates comprised a larger fraction of the total near-surface phytoplankton at stations in the far northeastern part of the lake arid at stations along the northern shore. While diatoms were dominant at some offshore stations, green algae made a more signif- icant contribution to the total assemblage in addition to somewhat lower and more variable fractions of mlcroflagellates. Although present at most stations sampled, the blue-green algae contributed a relatively small fraction of the total phytoplankton collected during May. A definite shift in the pattern of dominance was noted in the collections 121 MRY 15-19, 1972 TOWWIO OSHEGO MPrtlLTON NIRGHVI WVW ■VZOOO.OO -18000.00 12000.00 -12000.00 1-0 *■ Q *- Q ^0 '*°'^'*^^°' • Dl/tt • GN/ML • BG/MU » am. TOROKTO OSHECO MPMILTGN XlflCPflfl WVEB \2000.00 ISOOO.OO \2000.00 iZOOO.OO Iq Iq i-0 ^0 FIG. 13. Areal distribution of major phytoplankton group cell counts, 122 MttllLTi JULY lO-m. 1972 WVEPI ■ilOOO.OO TlOOO.OO TlOOO.OO -11000.00 Xq ifl iQ ^0 '''**^^°* » 01/H. « GN/MU « BG/ML • nvtt Tonomo AUGUST 21-2U. 1972 MflrirUON NlftGNVl WVEB WJCHESTER 11000.00 11000.00 11000.00 IlOOO.OO Xo ^0 Xq lo » 01/ML » GfVML • BG/H. ■ FL/MU FIG. 13 continued. 123 OCT 30 - NOV 3. 1972 HRHIUTON WVEB roCHESTER •1800.00 -iSOO.OO -1600.00 *- *• *- ■1600.00 ^ » DI/^&. » sum. » BG/ML « Ft/ML NOV 27 - DEC 1. 1972 HRMiaON HlfiCflBfl WVER ROCMESTEft •1600.00 -1600.00 -1600.00 -1600.00 i-0 *-0 *-0 1-0 ■ Ol/n. m Oi/TL • BC/It. « nVML FIG. 13 continued. 124 FEBRURRY 5-9. 1973 HlRGFfift RIVER ROCHESTER OSWEGO •1600.00 •J600.00 -1600.00 Teoo.oo i-0 5-0 *-0 1-0 • OI/ML ■ GN/HL » 8G/ML » a/ML MARCH 19-22. 1973 lOROfro MPtllUON HlfCPPR RIVER 1000.00 illOOO.OO -1,1000.00 \1000.00 ROCHESTER •1100( i- • 01/rt. • CN/ML ■ BG/HL « FlAt, FIG. 13 continued, 125 RPRIL 24-28. 1973 rmiLTON NlfCfifW WVER OSHEGO ■12000.00 "1,2000.00 12000.00 "12000.00 1-0 ^0 1-0 ^0 l'0Q€S1V^ , oi/ML » GN/M. • BG/ft. « a/«L TOBONTO JUNE 11-14, 1973 HRMILTON HJBGflPfl WVEft "12000.00 "12000.00 "12000.00 "12000.00 iO ^0 1-0 ^0 '*°'^*'^^^'^ • DI/ML » GN/J*. » BG/ML • FL/ML FIG. 13 continued. 126 taken during the June 1972 cruise. While diatoms were dominant at stations in the northwestern sector of the lake and at certain stations in the northeastern part, microflagellates had become a much more relatively important part of the flora at stations in the southeastern sector, A relative increase in the importance of green algae was seen at several stations, and they were co-dominant with the other major groups at several stations in the far southwestern and far northeastern parts of Lake Ontario, There was considerable regional variation in dominance patterns based on samples collected during July (note scale change) . An extreme peak in abundance of green algae was found at station 14 near Niagara, and this group was also relatively abundant at certain stations along the southern shore and at a group of stations in the eastern part of the lake. Diatoms remained dominant at stations on the western shore, between Hamilton and Toronto and at several offshore stations in the east central part of the lake, Microflagellate abundance was quite variable, although this group dominated several off- shore stations, particularly in the eastern half of the lake. During July, blue-green algae first became relatively important in the phyto- plankton assemblage, particularly at stations in the far eastern part of the lake and at certain stations along the southern shore. Siimples taken during the August cruise showed a considerable increase in the relative importance of green algal species, particularly at stations in the eastern part of the lake where they were dominant in the assemblages collected at most stations. Some increase in the relative importance of blue-green algae was also noted, although highest levels occurred at scattered stations. In October (note scale change) , however, this group became dominant at many stations. They were most important at a series of stations near mid-lake, while in other areas, particularly in the eastern half of the lake, assemblage abundance wag more evenly distributed among the major groups. While the green algae generally declined in relative importance in this set of samples, the d:iatoms again became dominant at isolated stations along the western and southern shores. Somewhat surprisingly, the dominance of blue- green algae was maintained into the Nov^ber 1972 sampling period. This group was either dominant or co-dominant with the diatoms at many stations, although the latter group was significantly more abundant tltian any other at many nearshore stations throughout the lake. By February 1973, the blue-green algae had declined to insignificant levels at most stations sampled although a few relatively high population densities were still found. Diatoms were dominant at most stations, with relatively minor contributions from other groups. In March, diatoms were dominant at nearly all of the stations sampled, with minor contributions from the other groups. The proportion of the total phytoplankton assemblage contributed by this group was especially large at stations near shore, apparently as a result of the initiation of the spring diatom bloom. Approximately the same situation was pres- ent in the April samples (note scale change) , Diatoms were dominant at all stations, with very minor contributions from the other groups. It did appear, however, that there was an increase in the importance of microflagellates relative to the other minor components of the flora. 127 In June there was a dramatic increase in the relative importance of microf lagellates . At the time our samples were taken, this group was dominant at most offshore stations and co-dominant with diatoms at many nearshore stations. Unlike the previous two months, the other two major groups, particularly the green algae, had begun to increase and consti- tuted a still minor but appreciable part of the total phytoplankton flora, especially at stations nearest shore. Diversity Trends in Near-surfaoe Waters The Shannon-Weaver index, a gross measure of assemblage structure, was calculated for near-surface phytoplankton assemblages analyzed during the course of this investigation. Although the results of any such integrative measure should be Interpreted with caution, certain inter- esting patterns are present in Lake Ontario. The calculated diversity of most samples taken during the May cruise (Fig, 14) was uniformly rather high, with values less than 2.0 being found only at stations 69, 71 and 85 in the east central part of the lake. Samples taken during June 1972 also showed relatively high diversities at most stations,^ however, values below 2.0 were found at stations 92 and 105 in Mexico Bay and at a group of stations in the south central part of the lake, including shoreward stations between Rochester and Niagara and extending out to mid-lake stations. Average diversity decreased significantly during July, and the apparent pattern of the previous month was reversed. Most stations sampled during this month had diversities less than 2.0, and higher values were restricted to a group of near- shore stations in the far western part of the lake near Hamilton and Toronto, stations 90, 92 and 105 in the Oswego-Mexico Bay region and a group of stations in the central portion of the lake extending from the north to the south shore. In August the average diversity at sta- tions sampled again increased, and values greater than 2.0 were found at most stations. Diversity values less than 2.0 were found only at stations 12 and 14 near Niagara, a group of stations extending from 8 and 19 near Toronto out to near mid- lake, and stations 54 and 56 in the central part of the lake. In October, average diversity values were slightly depressed, and scattered values less than 2.0 were found at stations throughout the central portion of the lake and at a few stations near shore. Average diversity values remained over 2.0 in samples collected during November 1972. Significantly lower values were found at a group of stations in the northwestern sector of the lake running from the Toronto vicinity to near mid-lake, and at a group projection from stations 72 and 73 east of Rochester northward into the lake. The former pattern was quite similar to that found in the August samples. In February 1973, the only samples which had cal- culated diversities less than 2.0 were mid-lake stations 46 and 77 and station 60 near Rochester. In March, diversity values less than 2.0 were restricted to certain stations near the southern shore. Included In this group were stations 89, 90 and 105 In the Oswego- Mexico Bay vicinity, station 60 near Rochester, and station 30 east of Niagara. A somewhat similar case was apparent in the April samples. 128 TOROtno MRT 15-19, 1972 wvoi POCHESTEB TOfflHTO JUNE 12-16. 1972 Kirerrfli P0QC3TEB FIG. 14. Assemblage diversity (Shannon-Weaver index), 129 JULY 10-lU. 1972 TOBOmO WfCFrs (OChtSTER RUGUST 21-214. 1972 Torano ROCHESTEB FIG. 14 continued. 130 OCT 30 - NOV 3. 1972 TORano fOQCSTEFt NOV 27 - DEC 1.. 1972 TORONTO POCHESTEB FIG. 14 continued. 131 FEBRURRT 5-9, 1973 TOROMTO KPCW Mvfa roCHESTEB MRRCH 19-22. 1973 TDBOMTO MVOt foocsTtn FIG, 14 continued, 132 RPRIL 24-28. 1973 TORcmo POOESTER JUNE 11-14. 1973 TORCKTO ROOESTER FIG. 14 continued. 133 The only samples from this cruise having diversities less than 2.0 were collected at nearshore stations 42, 60 and 72 in the Rochester vicinity and station 1, north of Hamilton. In June 1973 a rather dramatic rever- sal of the usual pattern, somewhat similar to the case found the previous July, was noted. Average assemblage diversities declined substantially, and the only samples having diversities greater than 2.0 were collected at nearshore stations, and primarily in areas which, on the basis of our other results, appear to be significantly enriched. Included in this group were stations 8 and 19 near Toronto, station 30 east of Niagara, stations 42, 59, 60 and 72 in the Rochester vicinity, station 105 in Mexico Bay, and a group of 6 stations in the northeastern part of the lake. Areat Distribution of Seleeted Species In the following section, data on the distribution of certain species and higher classification groups in the near-surface waters of Lake Ontario are presented. We have attempted to select those entities which are either particularly abundant in the phytoplankton assemblage or whose occurrence may be indicative of particular water quality con- ditions. Data are based on samples from 1 m depth. A brief discussion of the ecological affinities of the entities treated is given along with discussion of their abundance trends in Lake Ontario. Bacillariophyta Asterionetta jbrmosa Hass. (Fig, 15). This species is one of the most ubiquitous of all freshwater plankton diatoms. It is present in nearly all areas of the Laurentian Great Lakes. Slight morphological differ- ences suggest that there may be strain differences in populations occurring in areas with grossly different nutrient supplies, but recent revision of the genus (Koerner 1970) retains A. formosa as a single species. Hohn's (1969) study of plankton diatom populations in Lake Erie suggests that this species did not drastically change in absolute abundance during the period that Lake Erie underwent drastic apparent reduction in water quality. It was, however, reduced in relative abundance. Apparently this species can tolerate considerable eutrophication and is favored by increased nutrient levels. During the IFYGL sampling period on Lake Ontario it was present at most stations sampled throughout the year. During the May 1972 cruise, highest populations were noted at stations relatively near shore. Although still abundant in June of the same year, highest population levels were noted at mid-lake stations. Overall abundance of this species was considerably reduced by July, although fairly high counts were noted at a few offshore stations. Populations reached and re- mained at low levels during August and October 1972. Slight increases were noted during the November 1972 and February 1973 cruises. The earliest indication of a spring bloom of this species was considerably 134 MAY 15-19. 1972 lOBONlO HRHIUON NIPGflRfl RIVEH ROCHESTER 70R0MT0 JUNE 12-16. 1972 umiaoN fWCHESTER FIG. 15. Distribution of Astevionella fovmosa. 135 JULY 10-m. 1972 TORONTO t*HIUON NTfiGffV) ROCHESTER TOROKTO t«1IL70N RUGU3T 21-2'4. 1972 RIVER ROCHESTER FIG. 15 continued, 136 lonoMio HRHILTON WVER OCT 30 - NOV 3. 1972 ROCHESTER TORONTO MBMILTON HlfiGRRft RIVER NOV 27 - DEC 1. 1972 ROOCSTER FIG. 15 continued. 137 TORONTO HBMILTON NlftGfW) WVEft FEBRURRT 5-9. 1973 PIOCHESTEn TORONTO MRRCH 19-22. 1973 HRMiaON NlfiKWl RIVER ROCHESTER FIG. 15 continued. 138 TOnONTO HRMILTON NlfiGORfl RIVER APRIL 24-28, 1973 roOCSTER TOROKTO HHIiaOH NIP3RRR niYEH JUNE ll-m. 1973 ROOCSTEfi FIG. 15 continued. 139 elevated population densities noted at stations in Prince Edward Point area during the February sampling period. During March 1973, popula^ tion densities of A. formosa remained high at stations in this region, and similarly elevated levels were noted at a few other nearshore stations. By the April 1973 sampling interval, very high population levels were found at most stations relatively near shore. As in the previous year, by June 1973 populations were significantly reduced at nearshore stations, although remaining high in the south central part of the lake. Coscinodisaus subsalsa Juhl.-Dannf. (Fig. 16). If a single diatom were to be chosen as being indicative of extreme disturbance in the Laurentian Great Lakes, this species would be a prime candidate. It is apparently tolerant of extreme levels of nutrient enrichment and conservative element contamination. In Lake Erie it is one of the species which have shown the greatest increase between the 1938-1940 period and 1965 (Hohn 1969). According to Hohn's results it was exceedingly rare in Lake Erie prior to 1950. Although present in Lake Michigan, its distribution is almost entirely restricted to polluted harbors and adjacent nearshore areas (Stoermer and Yang 1969). Even in highly disturbed areas its numerical abundance is not particularly great compared to some of the other pollution-tolerant taxa, but because of its relatively large cells it contributes considerably to the biovolume of the assemblage (Hohn 1969). Unlike most diatom species, C. subsalsa apparently requires relatively high temperatures for maximum growth, and population maxima usually occur in the late summer and fall. During the IFYGL sampling period on Lake Ontario this seasonal preference was quite evident. During the May 1972 cruise it was found at a single station in Mexico Bay. In the June 1972 samples it was detected at two stations, also in the eastern part of the lake. In both cases population levels were very low. In the July 1972 samples, higher populations were found at two stations in Mexico Bay and by August at all stations east of Oswego and Pt. Petre. This species was detected also at stations 72 and 73 east of Rochester and 49 and 66 in the Presqu'ile Bay - Scotch Bonnet Lt. area. The latter pattern is particularly interesting since it is repeated in the November results. Samples taken during October 1972 showed a reduction in the number of stations occupied by C. subsalsa^ but relatively high population levels were still present at some stations in the eastern part of the lake. A similar pattern was noted in the November 1972 samples. In February 1973 this species was noted at a single station near Niagara and only at a few scattered stations, primarily in the eastern part of the lake, in March and April 1973. The only apparent consistency in these months was its occurrence at station 90 near Oswego. It was not noted in our June 1973 samples. Diatcma tenue var. elongatvjn Lyngb. (Fig. 17), Available information suggests that this species was introduced into the waters of the 140 TOROr^TO HfirtlUl NIflCWfl BIVEfl MAT 15-19. 1972 BOCHCSrw TOBOWTO »«irLTi RIVER JUNE 12-16, 1972 R0CJC3TEB FIG. 16. Distribution of Cosoinodiaaus subsalsa. 141 TORONTO MfiMrUOr. NIflCfiflfl BIVER JULY 10-14, 1972 WCHESTEB TOROtnO NlBSfifW RIVER fiUGUST 21-24, 1972 ROCHESTOJ FIG. 16 continued. 142 TOOONTO HRHILTO NIRGflrlfl BIVEB OCT 30 - NOV 3, 1972 pocHEsreB TOPOiffO HfWILTOH Hlft^lftft NOV 27 - DEC 1. 1972 WXHESTEB FIG. 16 continued. 143 fOPCKtXO HRMILTl NJfiGRRfl BIVEB FEBRUflRT 5-9, 1973 BOCtlESIER TOBCWTO HflMILTf NIRSflflfl Bivefl MRRCH 19-22, 1973 BOQCSTER FIG. 16 continued. 144 TOflOWTO MmiLTON NlfiGRW BIVEfl APRIL 24-28. 1973 BOOeSTEB TOBWfrO HfiMILI NlBGfWfl BIVEfl JUNE ll-m. 1973 nKHESTEB FIG. 16 continued. 145 TOfwjmo HPMIUON Nincrew WVEB MRT 15-19, 1972 POCHESTER 70B0NID MfiMIUON BlVtfl JUNE 12-16. 1972 BOCMESTEft FIG. 17. Distribution of Diatoma tenue var. etongation. 146 JULY 10-m. 1972 TORONTO HRMIUON NinSflFW RIVER ROCHESTER TORONTO HHI1IU0N NIBGWfl RIVER AUGUST 21-2ii, 1972 ROCHESTER FIG. 17 continued. 147 TORONTO HFWILTON RIVER OCT 30 - NOV 3. 1972 ROCHESTER TORONTO HflrtlLTON NIRCiPRfl BlVtft NOV 27 - DEC 1. 1972 ROCHESTER FIG. 17 continued. TOBOmO HfiMIUttN NIRGFIflfl RIVER FEBRUfiRT 5-9, 1973 ROCHESTER lOROinO HFIMIUON MRRCH 19-22. 1973 NIflGWV) RIVER ROCHESTER FIG. 17 continued. 149 Towno HfiMlLTON HIRGSfif) BIVEfl APRIL 24-28. 1973 ROaCSTER TORONTO MfiMIUOH NIRGrflfl WVLO JUNE 11-14. 1973 ROCHESTER FIG. 17 continued, 150 Liiurentlan Great Lakes only after a considerable degree of disturbance had taken place, Hohn C1969) lists it among the species which were absent or only rarely noted in historic collections from Lake Erie but which has become a major dominant in the past few decades. Similarly, Stoeriaer and Yang (1969) did not find it in very early collections from Lake I^ichigan although It was present there as early as 1932 (Ahlstrom 1936) and became abundant as early as 1946, At the present time it occurs throughout Lake Michigan and is especially abundant in nearshore waters and in polluted harbors. It has been widely reported from Lake Ontario (Nalewajko 1966; Michalski 1968; Reinwand 1969; Munawar and Nauwerck 1971), Most of these authors report D. tenue var, elongation as being particularly abundant in winter and early spring collections. Like many species with similar patterns of occurrence in the Great Lakes, D. tenue var. elongation appears to be favored by elevated levels of conservative ions (Huber-Pestalozzi 1942) as well as nutrient pollution. In samples collected during our May 1972 sampling cruise, low level populations of this species were noted, particularly at nearshore stations. Population densities exceeded 100 cells/ml in only one sample, from Mexico Bay, collected during this cruise. Increased population densities were noted in collections taken during June, particularly at stations east of a line from Oswego to Point Petre. A continued increase was noted in collections taken during July, with a tendency for highest population densities to occur in the southern half of the lake. By August these populations had been considerably reduced and remained at low levels during the October and November 1972 and February and March 1973 cruises. In April 1973, one population exceeding 100 cells/ml was noted in the eastern part of the lake, and there appeared to be a general increase in the population density at nearshore stations. As had been the case the pervious year, Z?. tenue var. elongatum bloomed at stations in the eastern part of the lake in June 1973. Fragilaria oapuaina Desm. (Fig. 18) . The world distribution records of this species suggest that it is primarily a littoral species which can become important in the plankton of eutrophic lakes (Huber-Pestalozzi 1942). Hohn (1969) reports that it has become a dominant in western Lake Erie since 1950 and may comprise as much as 90% of the total phyto- plankton assemblage at certain stations in the island area of that lake. According to Stoermer and Yang (1969), low level populations were pre- sent in historic collections from Lake Michigan, however abundant occurrences are largely restricted to highly eutrophied areas such as certain harbors and southern Green Bay. It has been noted as being abundant in Lake Ontario by some Investigators (Nalewajko 1966; Reinwand 1969) but not reported by others. Michalski (1968) Indicates it is more abundant in the Bay of Quinte than in Lake Ontario proper. Its tendency to occur in very large colonies leads to large uncertainties in estimates of its abundance made by standard plankton counting methods. Only low population levels of this species were noted in our samples from 151 TOftONTO HRdlUON HlfiGORH BlVEfi MRT 15-19, 1972 roCMESTEB TORONTO tfWIUON NIHGPflfl RIVER JUNE 12-16. 1972 ROaCSTEB FIG. 18. Distribution of Fragilavia aapuoina. 152 JULY 10-14. 1972 TOKKrO HBMILTON RIVER fWQCSTEB TORONTO tWIILTON AUGUST 21-24. 1972 NlftOfvlR BIVEB BOOCSTER FIG. 18 continued, 153 TOWNTO HRHILTON WVBrt OCT 30 - NOV 3. 1972 ROCHESTEB TDPOrfTO tfwiuort KlfCPBfl RIVEB NOV 27 - DEC U 1972. BCX>£STEn FIG. 18 continued, 154 FEBRUARY 5-9, 1973 TORONTO HfirtiaON NIBGPRB RIVER ROCHESTER MflRCM 19-22. 1973 TORONTO HRhlLTON RlVtfl ROCHESTER FIG. 18 continued. 155 TOBOMTO HRMILTON NIRGfififl RIVER APRIL 24-28. 1973 fOCHESTER lOBOmO JUNE 11-14. 1973 HflfllLTON NlfiGflfiR WVEB RtxatstDi FIG. 18 continued. 156 the May 1972 cruise. In the June samples, high population densities were noted at a few isolated nearshore stations, although this species was not particularly abundant at most stations. The high populations noted the previous month had declined by July, and only a few low-level occurrences were noted in collections from that month. Increased population densities were noted at several stations in the eastern part of the lake and at station 2 near Hamilton during the August cruise. The greatest abundance of F. aapuoina found during the IFYGL field sampling period occurred during the October cruise, when very high populations were found at two stations near the southern shore and relatively high population densities were noted at several offshore stations. In samples from the November 1972 cruise, high population densities were again restricted primarily to stations nearest shore, and by February 1973 F. oapuoina was noted only at station 14 near Niagara and station 90 near Oswego. In our samples from PEarch 1973, high pop- ulation densities were noted at stations 79 and 96 in the eastern part of the lake and minor increases at several other stations. Further increases, again primarily at stations nearest shore, were noted in samples from the April cruise. In June the number of stations having high population densities of F. oapucina decreased, but one abundant occurrence was noted off shore at station 45. Fragi-laria orotonensis Kitton. (Fig. 19). This species is one of the most common and widely distributed of all freshwater plankton diatoms. It is apparently able to tolerate a wide range of ecological conditions, and populations are found in nearly all areas of the Laruentian Great Lakes. Some evidence of its adaptability is apparent in Hohn's (1969) finding that it was one of the species whose absolute abundance had not changed appreciably in western Lake Erie over the past several decades. Stoermer and Yang (1969) have speculated that its apparently wide range of tolerance may be due to the fact that several races or cryptospecies are included in the commonly accepted concept of the species, but firm evidence for this is lacking. This species was abundant at several stations in the eastern part of the lake and some nearshore stations, particularly on the northern shore, on the basis of samples taken during the May 1972 cruise. Some general increase in population density was noted during June, again particularly in the northern half of the lake. Apparently these populations were reduced by July, and significant populations were found only at a few mid-lake stations and two stations in the western end of the lake. In August, however, population densities apparently increased again, and significant populations were found at most stations throughout the lake. Population levels were reduced in samples obtained during October and November 1973, although F, orotonensis remained widely distributed in Lake Ontario. This reduction in population density apparently contin- ued, since only a few low-level populations were found in the February 1973 samples. Samples taken during March showed slight increases at a few stations relatively near shore, and by April significant popula- tions were again present at stations in the eastern part of the lake 157 MAT 15-19. 1972 TOpONTO HRMILT NIRGORO BIVEB BooesTen TORONTO JUNE 12-16. 1972 MfifllLT NIBGPflfl BIVEB BOQtSTEB FIG. 19. Distribution of Fragilaria arotonensis. 158 TORONTO wwraoN NIPGflfifl RIVEP JULY 10-14. 1972 ROCHESTEH TORONTO fiUGUST 21-24. 1972 KPMraoN RIVER ROCHESTER FIG. 19 continued. 159 TORONTO WWrUTOfJ OCT 30 - NOV 3. 1972 8IVEB fWaCSTEP TORONTO HRMILTQN NOV 27 - DEC 1. 1972 NIBGOafl RIVEfl ROCHESTER FIG. 19 continued, 160 T080NT0 HRMILTW NIBGflBfl PIVEB FEBRUnRT 5-9, 1973 fWCHESiefi Topcmo HfifirUTi nnnCH 19-22. 1973 fiOaCSTER FIG. 19 continued. 161 TORONTO HRMiaa» NIfiSfirlR RIVEP APRIL 24-28, 1973 fiOCHESTER TORONTO JUNE 11-14. 1973 HRMILTQ- NlfWtafl BIVtR RoaesTEfi FIG. 19 continued. 162 and along the north shore, High levels of F, crotonensis were noted at numerous stations in the June 1973 samples, as in the previous year. V Melosira islandiaa 0, Mull, (Fig, 20), This species is a common domi- nant in large temperate lakes. Although it is apparently not tolerent of high degrees of eutrophication, it is abundant in most areas of the Laurentlan Great Lakes. Hohn (1969) indicates that it is not present in abundance in Lake Erie, and Holland (1968) has shown it is much less abundant in highly eutrophic regions of Green Bay than it is in the offshore waters of Lake Michigan. Nalewajko (1966) found it to be relatively much more abundant in collections from offshore stations in Lake Ontario than it was in nearshore stations. Most literature sources indicate that M. -Lslandioa reaches its maximum abundance at water temper- atures less than 12°C, and Munawar and Nauwerck (1971) found it to be a spring dominant in Lake Ontario, Sizable populations were present in most of our samples from May 1972, although there was a tendency for lower populations to be present at mid-lake stations. The highest population densities noted during our study were found in the June 1972 samples. At this time most stations sampled had significant populations of M. ■istand.-ioa but there was a tendency toward reduced population densities at stations near the American shore, particularly in the Rochester vicinity. By July, populations had been strikingly reduced, and this situation continued through the August, October and November sampling period. Slightly increased abundance was noted at some inshore stations sampled in February, and the beginning of the spring bloom period was visible in our March results. In 1973, highest population densities were found in the April samples, although there was still a clear difference in abundance between the mid-lake and shoreward areas at the time the samples were taken. In striking contrast to the previous year's samples, populations of this species had collapsed at all but a few mid-lake stations by June 1973. N-itzschia baaata Hust. (Fig. 21). Although the reported distribution of this species is primarily restricted to large, tropical lakes (Hustedt 1949), populations occurring in the Laurentian Great Lakes appear to be morphologically identical to typical populations. Although Stoermer and Yang (1969) have recorded this entity from a number of localities in Lake Michigan, other reports from the Great Lakes are lacking. So far as previous reports from Lake Ontario are concerned, we suspect that this species has been included under N. aciaularis which it somewhat resembles, and perhaps Synedra spp. which are exceedingly difficult to distinguish from planktonic Ni-tssckias in settled pre- parations. In our collections this species was relatively abundant at nearshore sta- tions sampled during May 197 2, and smaller populations occurred at most offshore stations. It apparently continued to increase in abundance at 163 my 15-19. 1972 TOfiOtnO HftMILTON NIRGaHfl RIVER ROCHESTER TORONTO MRilLTCW RIVEB JUNE 12-16. 1972 ROOtSTEft FIG. 20. Distribution of Melosira i-standiaa. 164 TORONTO NIRGflflfi BIVEB JULY 10-14. 1972 fWSCSTER TOBOtiTO MflMILT NIfiGA'W RIVEfl RUGUST 21-214, 1972 BOCHESTm FIG. 20 continued, 165 TOBOKTO MBhlUTOrt NIRGWfl MVEfl OCT 30 - NOV 3. 1972 roctesTEB TOBOMTO HmrtT' PIVEH NOV 27 - DEC 1. 1972 BOOCSTER FIG. 20 continued. 166 TOKWTO MRMILTON NIflGflflft BIVEB FEBRUfiRT 5-9, 1973 BOCItSTEB TOBOmo MflRCH 19-22. 1973 HAMILTON NJfiGfiRR Riven B0QC3TEB FIG. 20 continued. 167 TORONTO WHILTON RIVEB APRIL 24-28. 1973 BOCHESTEB TORONTO HflrtlUON NIRGR^fl BIVEfl JUNE 11-14. 1973 ROQCSTEP FIG. 20 continued. 168 MOT 15-19, 1972 TOBOKTO MfiNIUaS BIVEP ROCHESTER TOBOmO JUNE 12-16. 1972 HaniLTa KlfiGfpf) RIVtR POCHESIEB FIG. 21. Distribution of Nitzschia bacata. 169 JULY 10-1^. 1972 TOPOtfTO HfWIUW NIfiGflfW RIVEB fiOQCSTEB AUGUST 21-2ii. 1972 Httiia NlfiSftW filVEfl TOCMESTEfl FIG. 21 continued. 170 TOfWJKTO fWn-TON OCT 30 - NOV 3. 1972 NIBGR8P RIVER BOCHESTER TOBCNTO MWRTON NOV 27 - DEC 1. 1972 NIPOWI RIVER ROQCSTER FIG. 21 continued. 171 FEBRURRT 5-9, 1973 TOWfTO MRMIUaN NlflGflRfl BIVEB ROOCSTER TORONTO ttWlLV MARCH 19-22. 1973 NIRUR=if) PIV£R fWDCSTEP FIG. 21 continued. 172 TORCmO tWILTON RPRIL 2LI-28. 1973 NIRGfiRfl RIVEfi BOCHESTEB TORONTO t««IUON NIBCmfl BIVEB JUNE 11-14. 1973 ROCHESTER FIG. 21 continued. 173 most stations sampled during the June cruise, and populations were present at most stations except a series off shore in the southern half of the lake. This particular pattern was seen in several other species. By July, populations had drastically declined and only low-level populations were noted at scattered stations. This trend continued into August, when occurrences of this species were very scarce. Abundance of N. baaata increased again in October, particularly in the far western end of the lake, and scattered occurrences were noted in samples taken during 1972 and February 1973. In March, population densities increased markedly at a few stations in the eastern end of the lake, and there was a slight tendency toward higher numbers at stations throughout the lake. Populations peaked at stations throughout the lake in April 1973, but began to decline again, particularly at stations in the eastern half of the lake, in June. Nitzsohia dissipata (Kutz.) Grun. (Fig. 22). One of the most common and widely distributed members of the genus, N. dissipata, seems to be particularly abundant in the phytoplankton of the Laurentian Great Lakes. Although usually considered to be primarily a benthic rather than a planktonic species (Huber-Pestalozzi 1942), it was reported as a major species in some localities in western Lake Erie (Hohn 1969) and is apparently widely distributed in Lake Michigan (Stoermer and Yang 1969). According to Stoermer and Yang's study it was not noted in collections taken prior to 1937. Its wide distribution in the offshore waters of the Great Lakes is somewhat surprising, since some authorities consider it to be primarily a species of eutrophic habitats, and high population densities to be indicative of organic pollution (Choluoky 1968) . It has previously been reported as being common in certain localities in Lake Ontario (Nalewajko 1966; Reinwand 1969). Although never among the major dominants in our collections, this species is rather consistently present and displays a distinct seasonal pattern. It was present in relatively high numbers in collections taken during May 197 2, and slightly reduced in samples taken during the June cruise although it was still present at the majority of the stations sampled. In July, the abundance of N. dissipata was severely reduced and occurrences were largely restricted to stations nearest shore. This trend continued during August, with only one significant population, at station 60 near Rochester, and a few isolated occurrences at nearshore stations. Somewhat increased numbers were noted in samples taken during October, and populations were noted at several offshore stations although highest abundance was still restricted to nearshore stations. Approxi- mately the same pattern continued during the time period covered by the November 197 2 and February 1973 cruises, but there appeared to be less difference in population density of this species near shore compared to mid-lake stations. A distinct increase in the abundance of N. dissipata was noted in collections taken during March, and this trend apparently continued into April. By the time stations were sampled in June, popula- tions appeared to be on the wane again and population densities were, in general, lower than they had been the previous year. 174 TORtWTO HftttlLTCW NIBGfiRft WVEB MAT 15-19. 1972 fWOESTEB TOWKTO ? HfWIUON JUNE 12-16. 1972 NrBGP3a BlVtfl BOCtCSTEfi FIG. 22. Distribution of Bitzsdhia dissipata. 175 JULY 10-m. 1972 TCWONTO MflMILTON NlflGRIfl RIVEfl ROCHESTER AUGUST 21-2^1. 1972 TORONTO MfirtlUON NIfiGWPI RIVES ROCHESTER FIG. 22 continued. 176 OCT 30 - NOV 3. 1972 TOBOKTO MflHILTON NIBGfWl WVEP fUXfCSTER TOfWfTO HfifirUttN NOV 27 - DEC 1. 1972 NTflGffW BOCHCSTEfl FIG. 22 continued. 177 FEBRURRT 5-9, 1973 TOBOWTO MfitllLTON NlfiGRiq BIVEfi BOCHESTEfi TOfWJmO MfinCH 19-22. 1973 HfiHIUON PIVER WKHESTER FIG. 22 continued. 178 TORONTO HWILTON RIVEfl APRIL 24-28. 1973 BOCHESTEB TOfWWrO HflHiaON NIfiOftSR hIVEfl JUNE ll-m. 1973 BOCHESTEfl FIG. 22 continued. 179 Nitzsokia sp. (#2) (Fig. 23). This unidentified species of Nitzsahia, although never particularly abundant, is apparently widely distributed in the phytoplankton of the Great Lakes. Stoermer and Yang (1969) have recorded it from a variety of localities in Lake Michigan and our obser- vations indicate that it is also present in the other lakes. It some- what resembles E. l-Lnearis Wm. Smith, and some records of ff. linearis from the offshore waters of the lake may refer to the entity we treat here. Despite its consistently low levels of absolute abundance, the distribution of this species appears to be quite uniform and, because of its relatively large size, it probably makes an appreciable contri- bution to the biomass of the sparse winter phytoplankton in Lake Ontario. A number of populations of this species were noted in collections taken during the May 1972 cruise. Population densities decreased somewhat in our June samples, and there appeared to be a trend of higher population densities in the western part of the lake. Only isolated low-level occurrences were found in the July and August samples. Occurrences were noted at a larger number of stations sampled during August although population densities remained relatively low. Increased population densities were noted at a number of stations sampled during November 1972, and this trend was apparently continued in February 1973 despite the pronounced minimum in total phytoplankton density which occurred this month. Further increases in the abundance of this species were noted at most stations sampled on the March cruise, and the highest population densities found at any time during the IFYGL sampling period occurred at stations taken during the April 1973 cruise. The extremely high population densities noted the pre- vious month had apparently been substantially reduced by the time the June 1973 samples were taken, however significant populations of this species were still present at a number of stations. Stephanodisaus alpinus Hust. (Fig. 24). The ecological affinities of this species are difficult to determine because of the taxonomic confusion which surrounds it. It is apparently often confused with S. astraea and its varieties and to a certain extent with smaller species such as S. tenuis. According to Hohn (1969) it is one of the species which have undergone dramatic increase in Lake Erie in recent decades. According to Stoeirmer and Yang (1969) it has been present in Lake Michigan since the 1880' s and has not enjoyed any great increase in abundance during the period of record. Their results indicate that it is primarily a winter form in Lake Michigan. Previous records from Lake Ontario are lacking. Isolated populations of S. alpinus were noted in collections taken during the May 197 2 cruise, particularly at mid-lake stations. Popula- tions apparently declined by June and remained low during July and August. Populations began to increase again in October. After a slight apparent decrease in November, population densities of S. alpinus increased again in February 1973 and reached their highest levels in 180 TORONTO HRMILTDN RIVER MAY 15-19, 1972 ROCHESTER TOflOWTO JUNE 12-16. 1972 HRMaTON NIfiGftlfl RlVEfi ROOCSTER FIG. 23. Distribution of Nitzsahia sp. (#2). 181 TOROKTO HRHILTON NinsFira RIVQ4 JULY 10-14. 1972 ROCHESTER TOROKTO HflHtLTON NIfiGflSfl RIVER RUGUST 21-24, 1972 ROCHESTER FIG. 23 continued. 182 TOnONTO rUVER OCT 30 - NOV 3. 1972 BOCHESTER TORONTO WWILTON NOV 27 - DEC U 1972 NIRGftfW RIVER flOCHESTER FIG. 23 continued. 183 TOROWTO HfiNILTi NIRGflFta njVER FEBRURRY 5-9, 1973 RtttHESTER TORONTO MRRCM 19-22. 1973 HRNILTON RIVER ROCHESTER FIG. 23 continued, 184 J 7i APRIL 24-28, 1973 HFIHILTON NIRGfiRB BIVER KXHEsrm TORONTO HPHILT NlfWflfl RIVER JUNE 11-14, 1973 ROCHESTETt FIG. 23 continued. 185 MRY 15-19, 1972 10BQNT0 HFIHIUTON NlPGfltW WVEB TOCHESTER TORONTO HflMILTCN NIBCWfl ftlVER JUNE 12-16. 1972 ROCHESTER FIG, 24. Distribution of Stephanodisaus alpinus. 186 TORONTO NlflCflnfl WVEB JULY 10-14. 1972 ROCHESTER TOBOMTO KRMILTON WVEB AUGUST 21-214, 1972 ROCHESTER FIG. 24 continued. 187 10W3KT0 HPMILTON OCT 30 - NOV 3. 1972 NIBCflfW wvEn BOCHESIEB TOMKTO l«1IL70N BIVER NOV 27 - DEC 1. 1972 BOCHESTEB FIG. 24 continued. 188 TOBOMTO HBMILTON HIRGRfVl RIVER FEBRUfiRT 5-9. 1973 KJOCSTER TOfWWTO HmlLTftN MRRCH 19-22. 1973 NIfiGfiPfl BIVEfl ROCHESTER FIG. 24 ccmtinued. 189 TORONTO WtULTCN WBGflRfl WVER RPRIL 2U-28, 1973 ROCHESTER TORONTO MBMILTON HJBCanfl WVEft JUNE 11-14. 1973 R0O€STEn FIG. 24 continued. 190 SiSmples taken during March. In April, population densities declined drastically except at a few stations in the western part of the lake, and by June this species was essentially absent. S. atpinus is, thus, one of the few taxa present in Lake Ontario which shows a consistent increase in absolute abundance during the winter months. Stephanodisaus binderanus (Kutz.) Krieg. (Fig. 25). The presence of significant quantities of this species is considered to be indicative of degraded water quality conditions in the Laurentian Great Lakes. Hohn (1969) indicates that it increased greatly in abundance in Lake Erie between 1940 and 1965. In Lake Michigan it has caused significant problems at municipal water plants (Vaughn 1961) , primarily in the late winter and early spring. According to Stoermer and Yang (1969), S. binderanus is not indigenous to Lake Michigan but is now present in the nearshore waters in considerable abundance during the spring and main- tains populations in polluted harbors year-round. Most recent studies of Lake Ontario phytoplankton indicate that it has been abundant in recent years. It is difficult to arrive at a clear picture of recent and, particularly, historic trends because of the taxonomic confusion which surrounds most of the smaller species of Stephanodisaus. Like many of the phytoplankton species which have invaded the Great Lakes, S. bindevanus appears to be favored by both eu trophic conditions and considerable conservative element contamination (Huber-Pestalozzi 1942) . Some authorities (Cholnoky 1968) consider it to be primarily a brackish water form. Our records indicate that its optimum tempera- ture for growth is around g'C, and most world distribution records Indicate that it occurs in maximum abundance in the spring and fall. During the IFYGL sampling period on Lake Ontario, S. bindevanus was relatively abundant in samples taken from nearshore stations and stations in the far eastern part of the lake during the April 1972 cruise. At this time it was either present in only low abundance or entirely absent from mid-lake stations. In samples taken during June 1972, abundance declined somewhat in the Rochester-Oswego' area and in the far eastern part of the lake, but very high population densities were noted at nearshore stations in the northwestern part of the lake and at several offshore stations. As was the case with several other species, low abundance was noted at a group of stations offshore in the southern part of the lake. By the time of the July cruise, the high population densities noted the previous month had collapsed, although low densities of S. binderanus were still found at most stations sampled. Only very low abundance of this species was noted at stations during August. Slight increases were found during the fall cruises, particularly at stations in the far eastern part of the lake and at certain nearshore stations closest to major cities. Population densities remained low in samples taken during February and March 1973, but increased significantly in April. A continued increase was noted in samples taken during June 1973, but populations at no time approached the densities reached the previous spring. 191 tOWKIO HRMIUON NIRGfSRfl RIVER Wr 15-19, 1972 roCHESTER JUNE 12-16. 1972 HflttlUON MIRGftTfl RIVER ROCHESTER FIG. 25. Distribution of Stephanodisaus binderanus . 192 TOBOKTO HPWLTON NIfiGflPfl RIVER JULY 10-14, 1972 ROOCSTES lofvxao HWILIOH WVEB AUGUST 21-24, 1972 ROCHESTER FIG. 25 continued. 193 Towmo HflWUON HIBGfWI RIVER OCT 30 - NOV 3. 1972 ROCHESTER 70R0MTO tWHUOM RIV5J1 NOV 27 - DEC 1, 1972 ROCHESTER FIG. 25 continued. 194 TOftONTO HfiMILTON WPGffifl RIVEfl FEBRUARY 5-9. 1973 ROCHESTER HRfirUON NIfiGfiRfl RIVER MfiRCH 19-22. 1973 ROCHESTER FIG. 25 continued. 195 HfitllUON WfiGPfW WVEB RPRIL 24-28. 1973 ROCHESTER TOKWIO HnWUTON NIflC»Rfi RIVER JUNE 11-14. 1973 ROCHESTER FIG. 25 continued. 196 StephanodisGus hantzsohii Grun. (Fig. 26) . This species has long been considered a "form characteristic of strongly eutrophied waters" (Huber- Pestalozzi 1942) , and in the classical European literature it has been associated with water quality degradation in large, alpine lakes (Hustedt 1930). Like several other small species of Stephanodiscus which occur in eutrophied habitats, it is apparently favored by conservative element contamination and can tolerate brackish water. It has been widely re- ported from the Great Lakes, including the Bay of Quinte (McCombie 1967) and lake Ontario, where Munawar and Nauwerck (1971) cite S. hantzsohi'i var. pusitla as being a characteristic spring bloom form. However, confusion regarding its taxonomy makes it difficult to discern consis- tent patterns in its occurrence. Dtiring the IFYGL sampling period this species was abundant at most stations sampled during May 1972. Population densities declined at most stations sampled during June, and by July high population densities were largely restricted to a few mid-lake stations. Only scattered occurrences of S. hantzschii were found in samples from the August cruise, but populations of this species increased again in samples taken during October. This trend continued in November, and by February 1973 rela- tively high population densities were noted at stations near shore in the northeastern sector of the lake. By March there appeared to be a definite spring bloom at stations in the northern and eastern parts of the lake and an increase in population density at all nearshore stations. In our April samples, the very high population densities noted the previous month declined somewhat, but there was a tendency toward increase at most offshore stations, and very high population dssnsities were recorded at stations 20, 35, 36, and 48 along the northern shore east of Toronto. Population densities of this species declined significantly again by the June cruise. Stephanodisaus minutus Grun. (Fig. 27). This species usually occurs in the cold season phytoplankton of eutrophic or mesotrophic lakes. As is the case with other small species of the genus, distribution records are difficult to interpret because of taxonomic problems. Stoermer and Yang (1969) indicate that it is common in Lake Michigan and parti- cularly abundant in eutrophied nearshore areas and harbors . Dvjtring the IFYGL sampling period it was present at most stations sampled during the May 1972 cruise and tended to increase, particularly at stations in the northern half of the lake, by June. Population densities declined at all except a few mid-lake stations sampled during July, and by August only isolated low-level populations were present. Low population densities continued at all sampling intervals through February 1973. In March, however, this species began to increase, and by April substantial populations were present at most stations sampled, with highest population densities occurring at the shoreward stations. Counter to the trend shown by many diatom species, high population densities were again noted at stations sampled during June 1973. 197 MAT 15-19, 1972 TDROKTO tWMIUON HIBGflRfl RIVER ROCHESTER ■TORONTO WWILTON JUNE 12-16. 1972 NIRGfiRfl RIVER ROCHESTER FIG. 26. Distribution of Stephanodisous hantzsahii. 198 TORONTO HfitllLTON NinCPtV) RIVER JULY 10-114. 1972 ■ROCHESTER TORONTO HfniLTON NlfiGfiRfi RJVER AUGUST 21-2ii. 1972 ROOeSTER FIG. 26 continued. 199 TOKWTO HfiMILTON OCT 30 - NOV 3, 1972 NIRGHW RIVER ROCHESTER TOROKTO NOV 27 - DEC 1. 1972 HfWiaON N!fiGf«fl RIVEft ROCHESTER FIG. 26 continued. 200 TOROfnO HfVlILTON NIRGRfW WVER FEBRURRY 5-9. 1973 POCHESTER Tooomo MflDII. Nificqaq RlVcft MRRCM 19-22. 1973 ROCHESTER FIG. 26 continued, 201 RPRIL 24-28, 1973 TORorno HRrtlLTON NIRGflRPi ROChCSTER TOBtWTO JUNE 11-14. 1973 HWIILTOM ROCHcSTER FIG. 26 continued. 202 MAT 15-19. 1972 TORONTO HflMILTOM NIfiGfiRfl RIVER ROCHESTER TOROKTO JUNE 12-16, 1972 HflMlLTON NiflGflnfl RIVER BOOCSTER FIG. 27. Distribution of Stephanodisaus minutus. 203 JULY 10-14. 1972 TOROmO MflMIUON NIfiGfifW WVER ROCHESTER 70R0K10 fiUGUST 21-24, 1972 HRfllLTON NJfiGORfl RIVER ROCHESTER FIG. 27 continued. 204 TORONTO MPMILTON Nificma RIVER OCT 30 - NOV 3, 1972 ROCHeSTER TOROmO HonruTON Niflcwrw RIVEfl NOV 27 - DEC 1. 1972 ROCHESTER FIG. 27 continued, 205 TOBOKTO HflHILTON NlflSflfia RIVER FEBRUfiRY 5-9, 1973 ROCHESTER TORONTO MARCH 19-22. 1973 HflHILTON NIFCBRft RIVER ROCHESTER FIG. 27 continued. 206 RPRIL 214-28. 1973 7»3 70R0NTD HfWILTOS RIVtR ROCHESTER JUNE 11-14. 1973 milLTON RIYEJ^ ROOCSTCfl FIG. 27 continued. 207 Stephanodisaus subtilis (Van Goor) A. CI. (Fig, 28). The distribution and ecology of this very small and delicately structured member of the genus is very poorly known. According to Cleve-Euler (1951) it reaches its highest population densities in highly eutrophic and "slightly salty" waters. According to Stoermer and Yang (1969) it is abundant in eutrophied near shore waters and polluted harbors around Lake Michigan. Apparently it has not been reported previously from Lake Ontario although it may have been included in counts of other small members of the genus. In our May 1972 samples, relatively high population densities of this species were found at nearshore stations in the southeastern sector of the lake. By June this distribution pattern had changed rather dramati- cally, with highest population densities being found at stations in the northern half of the lake. On the basis of samples collected during July, populations tended to decrease in the coastal areas in the eastern part of the lake, while remaining high at nearshore stations in the western part and at certain mid-lake stations in the eastern part. By August population densities were significantly reduced except at a limited number of stations in the vicinity of Rochester. Abundance remained rather low at stations sampled during August, except for stations 2 and 3 near Hamilton. Relatively low population densities of this species were found at stations sampled during November, and this apparent decline continued during February 1973. On the basis of samples from the March cruise, it appeared that a nearshore bloom of this species was developing, but this trend was not evident in the April samples. The June 1973 samples showed increased population densities of S. subtilis at stations in the southwestern part of the lake, but the abundance of this species never approached the levels found the previous spring. Stephanodisaus tenuis Hust. (Fig. 29). This species appears to be associated with highly eutrophied waters in the Laurentian Great Lakes. Hohn (1969) lists it as one of the species which increased greatly in abundance in western Lake Erie in recent decades. It has apparently undergone similar increase in the eutrophied nearshore regions and polluted harbors bordering Lake Michigan (Stoermer and Yang 1969). On the basis of electron micrographs published by workers investigating the problem (Vaughn 1961) it appears that this species is, in fact, "the organism tentatively identified at S. hantzsahii" which caused, together with S. hinderanus, considerable problems at the Chicago filtration plant during the 1960's. It has been widely reported from Lake Ontario (Nalewajko 1966, 1967; Michalski 1968; Reinwand 1969; Munawar and Nauwerck 1971) and on the basis of these reports it appears to be consistently a dominant element of the spring diatom bloom. Sim- ilar to other small species of Stsphanodisaus which have become abundant in the Laurentian Great Lakes in relatively recent years, this organism appears to be favored by elevated levels of conservative ions as well as increased nutrients. In our May 1972 samples, population densities were high at stations 208 TOfrarrro HRMUON NlfiGffW BIVEB MAY 15-19. 1972 ROCHESTER TORONTO JUNE 12-16, 1972 HRfllLTON RIVER ROCHESTER FIG. 28. Distribution of Stephanodisaus subtitis. 209 HflMILION JULY 10-14. 1972 NlRSAiV) BIVEft ROCMESTEft T030N70 MfiMILTON WVOH AUGUST 21-24, 1972 BOCtCSTCR FIG. 28 continued. 210 OCT 30 - NOV 3. 1972 TOROmO HfiMinON NIRGFKVl WVER roCHESTEfi TW0N1O HfiWLTON NOV 27 - DEC 1. 1972 ROCHESTtR FIG. 28 continued. 211 TORONTO HfiMILTON NIRCnV) RIVER FEBRUnRY 5-9, 1973 ROCHESTER tOROmO HflMIUTON NlfWfiRfl RIVER MARCH 19-22, 1973 ROCHESTER FIG. 28 continued. 212 Tonomo HfiMILlON RIVER APRIL 24-28, 1973 FlOOCSTCfi TORONTO JUNE ii-14, 1973 HW1ILT0N NIBGWfi RIVtB ROCHESTER FIG. 28 continued. 213 •fORomo t««UON MlBGflRfl RIVER MRT 15-19, 1972 roCHESTER "TORONTO JUNE 12-16. 1972 HfWinON NIRGfWl RIVER ROCHESTER FIG. 29. Distribution of Stephanodisaus tenuis. 21A lomitoo hrmilton NlfiCWtf) RIVER JULY 10-14. 1972 ROCHESTER lOfVm MfirtlLlON HIBG!¥in RIVEB fiUGUST 21-24, 1972 ROCHESTER FIG. 29 continued. 215 TORONTO HfinlLTON NIBGflftfl WVER OCT 30 - NOV 3. 1972 ROCHESTER TORONTO HfiMIUON HIBGttW RIVER NOV 27 - DEC 1. 1972 ROCHESTER FIG, 29 continued. 216 TOROMTO MRMILTON NlflCfWl WVEft FEBRUnRT 5-9, 1973 ROCHESTEB MARCH 19-22, 1973 HfiMlL70H NIfiGWfl RIVtR BOCHESTEB FIG, 29 continued. 217 Ult TORomo HBMiaON NJBGflRfl MVEfl fiPRIL 24-28. 1973 ROCHESTER JUNE 11-14. 1973 MRMILTCW HIRGfWl RIVCB ROCHESTER FIG. 29 continued. 218 nearest shore in the southeastern sector of the lake and very low at most stations. By the June sampling period somewhat elevated counts were noted at offshore stations, but the very high population densities noted at nearshore stations the previous month had been drastically reduced. Populations continued to decline except at a few nearshore stations between Hamilton and Toronto in July, by August only a few low level occurrences were noted. During the October cruise, increased population densities were noted at several stations in the western end of the lake, but by the November cruise only very low population densities were pre- sent at the stations sampled. A slight increase in the abundance of this species, particularly in some of the stations nearest shore, was found in the February 1973 samples in spite of reduced total phytoplankton abundance during this month. Samples taken during 14arch 1973 indicated the beginning of a nearshore spring bloom of this species, particularly at station 60 near Rochester, and by April very high population densities were found at most nearshore stations in the eastern half of the lake. Population densities were significantly reduced at all stations sampled during June, except 'stations 7 and 8 near Toronto. Surirella angusta Kutz. (Fig. 30). The abundance and wide distribution of this species in the phytoplankton of Lake Ontario is extremely unusual. Although several species of the genus are successful in the plankton of large lakes, most previous studies would indicate that S. angusta is primarily benthic in habitat preference. Skuja(1956) lists it in his discussion of the Swedish limnoplankton, but emphasizes that it is very rare and probably accidental in such collections. Huber-Pestalozzi (1942) does not even mention it in his extensive treatment of the planktonic members of the genus. Stoermer and Yang (1969) list it from a number of localities in Lake Michigan, but always in very low abun- dance. Hohn (1969) lists it as occurring in Lake Erie, but does not indicate that it was particularly abundant in his collections. Previous investigations of Lake Ontario ])hytoplankton (Munawar and Nauwerck 1971) however, list it as one of the major winter dominants. Although the population densities achieved by this species are not particularly great, it may be of considerable ecological importance because of its relatively great cell volume and because it is apparently most abundant when other species are at their yearly minimum. The factors which allow this species, which is usually associated with benthic habitats in eutrophic systems, to become important in the plankton community of Lake Ontario are not readily apparent. In our collections from May 1972, S. angusta was present at most stations and quite abundant at many offshore stations. It declined drastically in the June samples and remained very scarce in the July and August collec- tions. Slightly increased population levels were noted in October col- lections, particularly at stations relatively near shore. This trend continued in the November collections, and into February 1973, when total phytoplankton abundance was at its yearly low. Population densities of this species remained relatively high in our March collections, and reached their seasonal peak in April 1973. By June 1973, population 219 TORONTO MBMILTON NlflGRW RIVER MAY 15-19, 1972 ROCHESTER TORONTO JUNE 12-16. 1972 HflMIUQN NlflGFW RIVER ROCHESTER FIG. 30. Distribution of Surivella angusta. 110 TORONTO MfWrUTi NlBGflafl RIVEfl JLTLT lO-m, 1972 ROCHESTER TORONTO HWrUT NIfl3,q3fl RIVIR RUGUST 21-2y.. 1972 ROCHESTER FIG. 30 continued. 221 OCT 30 - NOV 3, 1972 TORorno hflrtlUTO MVEB POCHESTEP TOBOKTO NOV 27 - DEC I. 1972 Hafiruc nOCHESTEfl FIG. 30 continued, 222 FEBRURRT 5-9, 1973 TORorno MflrtlLTON KlPGfifW RIVEfi ROCJCSTEB TWONIO MRRCH 19-22. 1973 WWILTON Bive« ROCHESTEfl FIG. 30 continued. 223 TORONTO MOMruTON RPRIL 24-28. 1973 NIBGPRfl ftlVER BOCHESTEfl TORONTO nfiflFLTON RIVER JUNE 11-14. 1973 ROChCSTER FIG. 30 continued. 224 levels had been reduced again to insignificant levels, Synedra ostenfeldii (Krieg.) A. CI. (Fig, 31). This species is one of the planktonic members of the genus which regularly occurs in colonies under optimal growth conditions. Individual cells are also found, especially following periods of peak abundance. The distribution and ecological affinities of this species are relatively poorly known. According to Cleve-Euler (1953) it is common in eutrophic lakes and rivers in Europe. Stoermer and Yang (1969) Indicate that it is widely distributed in Lake Michigan with highest population densities occurring in eutrophied nearshore areas. Apparently it has not been reported previously from Lake Ontario specifically, although it is undoubtedly containe>d in several reports of the genus. Although S. ostenfeldii was never particularly abundant in our collec- tions, numerous occurrences were noted, and it seems; to demonstrate a pronounced seasonal pattern of occurrence. Samples from the first cruise in May 1972 had few occurrences, although relatively large populations were noted at a few nearshore stations, particularly in the southeastern sector of the lake. Many more occurrences were noted in June samples, and highest population densities were found at stations in the eastern part of the lake which had not been sampled the previous month. Although occasional occurrences of this species were noted, its abundance remained low throughout the summer, fall, and winter sampling cruises. Samples taken during March 1973 showed slightly increased numbers, and a definite increase, particularly at stations in the far eastern part of the lake, was noted during April. Abundance increased further in June, with highest population densities occurring at offshore stations in the southern half of the lake. Tabellaria fenestrata (Lyngb.) Kutz. (Fig. 32). This species is among the most common and widely distributed of the freshwater plankton diatoms. It occurs in abundance throughout the Laurentian Great Lakes and seems tolerent of most conditions. According to Hohri (1969) it is one of the taxa whose absolute frequency has not changed markedly in western Lake Erie in recent decades, although its relative abundance has decreased because of the introduction of exotic dominants. Considerable contro- versy surrounds the taxonomy of this taxon (Knudson 1952; Koppen 1973), and the apparent extreme range of adaptability of this species may be due to failure to recognize the true genetic entities involved. During the IFYGL sampling period, this species was present at most stations in the northern part of the lake during the May 1972 sampling cruise and at a few other stations near shore. The same pattern continu£;d during June, when there appeared to be a well defined zone of non-occurrence of T. fenestrata at offshore stations in the southern half of the lake. These populations apparently declined and, by the time of the July cruise, high population densities were largely restricted to a few offshore stations. The single exception to this was station 19, 225 MAT 15-19, 1972 TOBOrfTO HBWLTON NlfiGftW wvm ROCHESTER JUNE 12-15, 1972 TORONTO HBniLTON NIPGffilH RIVER ROCtCSTER FIG. 31. Distribution of Synedva ostenfeldii. 226 TOBOWTO MfiHILTON NlflCflRR BIVE8 JULY 10-14. 1972 BOCfCSTEB TOBONTO rBrtlLTl mvEfl RUGUST 21-2ii. 1972 BOCneSTEB FIG. 31 continued. 227 Tow»no wniua- B1VE« OCT 30 - NOV 3. 1972 fWCtCSTtB lonorrro V 27 - DEC I. 1972 MflMIUaN POQCSrEB FIG. 31 continued. 228 T080MT0 WMILTCiN RIVER FEBRUflRT 5-9. 1973 BCOCSTEP TDROtno MARCH 19-22. 1973 NIRSRHfl RIVER BOOCSTEB FIG. 31 continued. 229 TOPONTO HfifllLTOrV NIPGfVffl RIVER APRIL 24-28. 1973 POCHESTEH TOBOtnO HfWILTON NIBGkHfl PIVLfl JUNE 11-14. 1973 POCHESTCR FIG, 31 continued. 230 Topomo HfiHILTW NIBGfftfl RIVER MAT 15-19, 1972 POCHESTEB TCPONTO HfWILTW RIVER JUNE 12-15. 1972 ROCHESTER FIG. 32. Distribution of Tabellaria fenestrata. 231 TOROrno tKWILTON NIRGfiRfl RIVER JULY 10-14. 1972 ROCHESTER TORONTO HftMILTON NlflOmfl RIVLH fiUGUST 21-24, 1972 R0QC3TER FIG. 32 continued. 232 T0W3NT0 MflMILTO NIfGffiO BJVEB OCT 30 - NOV 3. 1972 poa«st£« TOfWfTO NOV 27 - DEC 1. 1972 HRHILTON NJflGffW BOCHCSIER FIG. 32 continued. 233 FEBRURRY 5-9, 1373 TCRwno MBHILTQ- NIBGRRfl RIVEB POCHESTEB TORONTO MARCH 19-22. 1973 HftMILTOtJ NlftJDRfl RIVEfl POOeSTCP FIG. 32 continued, 236 TORONTO MRMILTOf) NIRGfBfl RIVER APRIL 24-28. 1973 POCteSTER TOFWrO JUNE 11-lLt. 1973 HfirtrLTCN NIPGFlfiR RIVER P0C31ESTER FIG. 32 continued. 235 near Toronto. The decline in abundance of T, fenestrata continued into August, when appreciable population densities were noted only at a few mid-lake stations and stations in the far western end of the lake. In October, however, population densities again increased at most stations. Population densities remained similarly high in samples taken during November, however there appeared to be a trend toward higher abundance at stations in the southern and eastern sectors of the lake at this time. By February 1973, population levels of T. fenestrata were con- siderably reduced, as was total phytoplankton density, except at stations 96 and 97 in the far eastern part of the lake. Reduced abundance was noted also in samples taken in March and April, with a tendency for highest population density to occur at stations nearest shore. Some increase in abundance of T. fenestrata was noted in June 1973 samples, however in 1973 populations appeared to be higher on the southern shore, unlike June 1972. Chlorophyta Ankistrodesmus falcatus (Corda) Ralfs (Fig. 33). Populations of this entity in Lake Ontario are somewhat unusual in that they generally fall in the lower size range commonly attributed to the species. Munawar and Nauwerck (1971), in their treatment of Lake Ontario phytoplankton, separated A. falaatus var. spirilliformis G. W. West from the nominate variety. All of the populations we have observed, however, tend to be intermediate in size and lack the characteristic shape of variety spiriltiforrrris and we chose to treat them under the nominate variety. Ankistrodesmus falaatus has been reported from many areas in the Laurentian Great Lakes, but high population densities are usually found only in eutrophied areas. Low level populations were noted at most stations sampled during the May 1972 cruise, and high population densities occurred at several nearshore stations between Niagara and Rochester. Population densities of this species increased at most stations sampled during June 1972. Highest densities were present at stations in the far western region of the lake near Hamilton and on the southern shore, with exception of the stations near Niagara, where abundance was notably reduced. In this month there appeared to be a consistent pattern of low population densities of this species at stations running from Niagara offshore in the southern half of the lake. Unlike most species associated with the spring bloom, A. falcatus never achieved particularly high abun- dance in the eastern sector of the lake. Samples taken during July showed a general reduction in density of ^4. falaatus , although signifi- cant populations were still present at stations nearest shore in the eastern part of the lake and in Mexico Bay. Although previous investi- gations have characterized Ankistrodesmus spp. as summer (Munawar and Nauwerck 1971) or fall (Michalski 1968) forms, populations were con- siderably reduced in our August samples and remained at low levels in samples taken during the fall and winter cruises. The same situation 236 TOBOWIO NlflCfiHfl RIVEfl MAY 15-19, 1972 BOCHESTEft TOROf/TO JUNE 12-16. 1972 BIVEfl BOCKESTEH FIG. 33. Distribution of Ankistrodesmus falaatus. 237 JULY 10-14. 1972 TOBCWO HRfirLTON MIRGflafl ROOCSTEfl TORONTO HfirtlLTON NIflCflRfl RIVEfl AUGUST 21-24, 1972 BOCHtSrEfl FIG. 33 continued. 238 TOfiONTO HfiMfUi HIRGfWft ftlVEfi OCT 30 - NOV 3, 1972 ROCHESIEfi lOfiOKIO RlVEfl NOV 21 - DEC U 1972 POCHESttfl FIG. 33 continued. 239 TOBOHTO HfiMIUi NIflCflRfl BIVEH FEBRUARY 5-9. 1973 POCHESTEfi TOBOMIO HfiMILTON RIVCH MARCH 19-22. 1973 ROCHES lEB FIG. 33 continued. 240 roKitno NlfCfififl RIVEfl APRIL 24-28. 1973 fwacsiEfl TOBOMTO HflMlLTON RIVEH JUNE U-m. 1973 RXHESrtR FIG. 33 continued. 241 obtained during the early spring sampling periods in 1973, and it was not until June 1973 that a few samples with population densities comparable to those found throughout the lake were found at stations near Niagara, If the lake-wide bloom of this species noted the previous year was repeated, this apparently did not take place until after termination of our sampling period. Botryoaoccus hraunii Kutz. (Fig, 34). This species has unusual distrib- ution, occurring in both eutrophic and oligotrophia lakes in consider- able quantities (Hutchinson 1967). Mature and scenescent colonies accumulate large quantities of fats and oils and tend to float near the surface. This, plus the fact that mature colonies are quite large, leads to uncertainties in estimates of its abundance made by standard phytoplankton enumeration methods. Although the distinctive colonies are visible in net plankton collections taken from almost any locality in the Laurentain Great Lakes during the late summer and fall, it is rarely reported in quantitative studies. In our collections its occurrence was very restricted. A single occurrence at about 75 cells/ml was noted at station 35 in May. Aside from this, all other occurrences noted came from the month of August. During this sampling period B. hraunii was present in considerable quantities at a number of stations sampled, particularly in the eastern' and northeastern parts of the lake. Coelastrum microporum Nag. (Fig. 35). This species is apparently quite widely distributed in the Laurentian Great Lakes, but only reaches appreciable abundance in eutrophic regions. Taft and Taft (1971) reports it from western Lake Erie, and we have observed it in collec- tions from several localities in Lakes Michigan and Huron. In these lakes it occurs in greatest abundance in shallow, eutrophied areas such as Green Bay and Saginaw Bay. It has been reported from Irondequoit Bay of Lake Ontario (Tressler et al. (1953) and as a spring dominant in the open lake by Munawar and Nauwerck (1971). Several other records of Coelastrum sp. from Lake Ontario are likely referrable to this species. It was not noted in our collections from the May and June 1972 cruises, and only isolated occurrences in the opposite ends of the lake were noted in July. By the time the August samples were taken, however, most stations sampled had populations of C. miaroponan, and it was quite abundant at stations in the eastern half of the lake. The population density of this species was greatly reduced in samples taken during October, and only a few populations were found in the November samples. A single occurrence was noted in samples taken during February, and it was apparently absent from samples taken during March and April 1973. In June 1973 a single, extremely high occurrence was noted at station 59 near Rochester. 242 MRY 15-19, 1972 TOficmo HfWILlON WVER ROOtSIER FIG. 34. Distribution of Botryoaoccus braunii. 243 TORONTO HfiMIUON NJfiGFfia RIViB JULY 10-14. 1972 ROCHESTER TOfiOKTO AUGUST 21-24, 1972 HPMILTON HlfiGWa RIVER ROCHESTER FIG. 35. Distribution of Coelastmm miavoporum. 244 "rOROKTO HRWLTON NIFIGffVI WVEB OCT 30 - NOV 3, 1972 BOCtCSTER TORONTO HRMIUON wvra NOV 27 - DEC 1, 1972 roCHESTER FIG. 35 continued. 245 70R0KTO HBHILTON NlfWWfl RIVER FEBRUARY 5-9, 1973 ROCHESTER TORONTO MPHIUTON RIVER MRRCH 19-22. 1973 ROCHESTEB FIG. 35 continued. 2A6 TOflONTO HPWLTW WrtR nPRIL 24-28, 1973 ROCHESTER TORONTO HRKILTON JUNE 11-14. 1973 BOQCSTEB FIG. 35 continued. 247 Gloeocystis planotoniaa (West & West) Lemm. (Fig. 36), This species has been reported from a variety of habitats in certain regions of Europe (Skuja 1956) and, although not widely reported from the Great Lakes, we have found it to be one of the more abundant green algae in the plankton of Lake Michigan. Skuja (1948) has given an excellent account of the life cycle stages of this species, and we suspect that some of the previous reports of Chlovella spp., Chlcmydomonas globosa Snow, and Gloeoaystis gigas (Kutz.) Lag. from Lake Ontario may be referrable to it. Moderate levels of abundance of this species were noted at stations along the southern shore in samples from the May 1972 cruise. By the time of the June cruise it had become widely distributed and populations were noted at most stations sampled, although there was a consistent pattern of non-occurrence at offshore stations in the southern half of the lake east of Niagara. High population densities were again noted in samples from the July cruise, especially in the southwestern sector of the lake and at isolated stations in the eastern part. An extremely high abundance of this species was found at station 14 near Niagara at this time. Somewhat reduced population densities were noted in the August samples, although the species was still present in significant quantities, particularly at stations in the northeastern part of the lake. Abundance of G. yZanotonica declined considerably in the October samples, and only scattered, low levels of occurrence were noted in samples from the November 1972 cruise and from the February, March and April cruises in 1973. Slightly increased levels of abundance of G. iplanctonica were noted in samples taken during June 1973, but population densities never approached those found the previous spring. Oooystis spp. (Fig. 37). The major population included in this category is 0, parva West & West, although minor populations of some of the other smaller species of the genus are present. Such species are a ubiquitous part of the stmmer phytoplankton in most parts of the Laurentian Great Lakes. In most offshore regions population levels of Ooayst-is spp. remain at low levels, although high population densities may be present in the more eutrophic regions. The entities included in this category showed a pronounced seasonality in our samples. Scattered, low level populations were found in May, June, and July 1973 samples. August samples showed a lake-wide bloom, with a trend toward highest population densities in the eastern portion of the lake. Abundance of the species progressively declined during the October and November sampling periods, and only scattered, low level populations were found in the 1973 samples. Fediastvim glandulifevi-n Benn. (Fig. 38). Although not widely reported from the Laurentian Great Lakes, this is apparently a fairly widely distributed euplanktonic species. 248 TORONTO HfieilUTON NIBGORR RIVER MRT 15-19. 1972 ROCHESTER TOROmO ^A HfltllUON JUNE 12-16. 1972 ROCHESTER FIG. 36. Distribution of Gtoeoaystis planotonica. 249 JULY 10-14. 1972 S1T2 TORomo HflMIUTON NlfiGflflfi RIVER ROCHESTER TORONTO RUGUST 21-24. 1972 HfitllLTOM NlRGfiflR BIVEft ROCHESTER FIG. 36 continued. 250 TOROKTO HRHILTON NlfiGP«fl R1VE8 OCT 30 - NOV 3, 1972 BOCMESTER NOV 27 - DEC U 1972 TOPONTO HRMiaON NIflGOOfl BIVEP ROCHESTER FIG. 36 continued. 251 TOWKTO HRMILTON ■NlfiGPRB mVER FEBRUARY 5-9, 1973 ROCHESTEfi TORONTO WKIILTON filVEtH MARCH 19-22. 1973 POCfCSTEB FIG. 36 continued. 252 APRIL 24-28. 1973 TOBCmO HHMILTON NIfiGfiRfl RIVER ROCMCSTEB JUNE 11-14. 1973 TOBOKTO HBHIUON Nifcma RIVER ROCHESTER FIG. 36 continued. 253 TOftono HBHILTON MRT 15-19. 1972 NIBGftH?) filVEB ROCHESTER TOfwno JUNE 12-lG. 1972 HRMILTON NIflGA'W RIVtfl ROCHESTER FIG. 37. Distribution of Ooaystis spp. 254 TOROmO HfiMILTW NIBGfW BIVEft JULY 10-14. 1972 ROCHESTER TOBOrnO AUGUST 21-24, 1972 MRMruaN BOCHESTEP FIG. 37 continued. 255 TOBONTO NIftSflfW RIVER OCT 30 - NOV 3. 1972 B0CHE3TEB TOftOrnO HflHILTON NIflGRflfl RIVCfl NOV 27 - DEC 1. 1972 BOOCSTEB FIG. 37 continued. 256 FEBRURRT 5-9, 1973 Tonomo HfWILTON NIBGBfiB BIVtR ROCHESTER TORONTO HfWILTON NIRGfian filVEft MRRCH 19-22. 1973 ROCHESTER FIG. 37 continued. 257 TORWIO MaMIUON NIPSRFlfl RIVEfi APRIL 24-28. 1973 ROCHESTER TOflOffrO fiRIILT*^ RiVER JUNE 11-14. 1973 ROaCSTER FIG. 37 continued. 258 TORONTO HfiMiaON NIBGfiPfl RIVER JULY 10-m. 1972 ROCHESTER TORONTO HfiHILTON RIVER fiUGUST 21-2'4, 1972 ROCHESTER FIG. 38 . Distribution of Pediastrim glandulifencra. 259 Its distribution in our samples from Lake Ontario is remarkably- restricted . A single occurrence was noted at station 14 near Niagara in July. In August it was abundant at all stations east of Oswego and Pt. Petre and somewhat smaller populations were found at nearshore stations ranging west from this region. No occurrences were noted in samples from cruises either before or after these two months. Phaaotus lentiaularis Ehr. (Fig. 39). This unusual chlorophycean flagellate has not been widely reported from the Great Lakes and relatively little is known about its distribution and ecological preference. We have found occasional populations in the in the upper lakes but it is usually a minor element of the flora. It is abundant in the summer plankton of some of the larger inland lakes in Michigan. In his review of the Swedish freshwater phytoplankton, Skuja (1956) indicates that it is widely distributed and is especially abundant in the summer. This tendency is strikingly apparent in our results. Significant populations of this species were not noted in our samples from May and June 1972. In July, populations were noted at two stations in Mexico Bay. By August it had apparently undergone a lakewide bloom since significant populations were found at nearly every station sampled during the August 1972 cruise. In the rest of the months sampled, relatively small populations were noted with some tendency for largest populations to occur at stations in the far eastern part of the lake and at stations nearest shore in other parts of the lake. Saenedesmus b-iceZluZaris Chodat (Fig. 40). Very little is known about the distribution and ecological affinities of this small species of Scenedesmus in the Laurentian Great Lakes. We have not found records of it from Lake Ontario, although specimens referred to S. bijuga and its varieties (Ogawa 1969; Munawar and Nauwerck 1971) may be included in 5. bicellularis as treated here. This species was very abundant at stations sampled during the first biology-chemistry cruise of the IFYGL during May and no particular geographical trends in its distribution were apparent. It continued to be very abundant at stations sampled during the June cruise, but at this time there appeared to be a consistent tendency toward reduced numbers at stations nearest the south shore of the lake. Unlike most of the species of green algae noted in the Lake Ontario phytoplankton, S. biaelluZaris had a pronounced summer minimum and the July and August samples contained relatively insignificant populations. A slight increase in abundance was found in samples collected during October, and small populations were also found in November 1972 and February 1973 cruises. Nearly stable populations were apparently present during March and April and, although significant increases in population density were noted at a few stations in the western part of the lake in June, the abundance of this species never approached the levels found the previous spring. 260 JULY 10-m. 1972 TOROfn-O MAilLTaN NIRSftSfl filVEB ROCHESTER AUGUST 21-2Lt. 1972 "n)«3tfro HWULION \ ROOCSTER FIG. 39. Distribution of Phaaotus lentiaularis . 261 OCT 30 - NOV 3. 1972 T080NTO HailLTOil RIVER TOOIESTEfi TORC»fTO MaiiuttN NOV _ 27 - DEC 1. 1972 NlfiSPftfl RIVER ROCHESTER FIG. 39 continued. 262 FEBRURRT 5-9. 1973 TOfWtno hfWlLTON NIBGflRfl BIVEB ROCHESTER MRRCH 19-22. 1973 Tbfwino HBttlUON BIVEfl iracHESTEn FIG. 39 continued. 263 TORONTO HfttULTON NIfiGflRfl WVEB APRIL 24-28. 1973 BOCtCSTER TOWWTO HfinlLTON NIfiS.'W BJVEfl JUNE 11-14. 1973 TOOCSTEfl FIG. 39 continued. 264 MAT 15-19. 1972 TOROmO HfiMIUON NIftGfiRa RIVEfl BOCHESTEft t¥Vi RIVER JUNE 12-16, 1972 ROCHESTER FIG. 40. Distribution of Scenedesmus biaellulavis. 265 Taiorno fflMILTOS NlflGflfW BIYEft JULY 10-14. 1972 ROCHES! EB TORCWTO RUGUST 21-24, 1972 MfiHIUO,N RIYtR ROCHESTER FIG. 40 continued, 266 TOBOKTO HflWLTON NIfiGflffl RIVER OCT 30 - NOV 3, 1972 ROCHESTER TOR!WrO HflfllLION NlflCTfifl RIVtR NOV 27 - DEC 1, 1972 ROOCSTER FIG. 40 continued. 267 TOROmO HfiMILTON NIB3KW RIVER FEBRURRY 5-9, 1973 ROCHESTER TOROKTO r«iiuoN NlBGWft RlVtft MRRCH 19-22, 1973 ROCHESIER FIG. 40 continued. 268 TOROnO HWIinON R]VE« APRIL 24-28, 1973 ROCHESTER TOROtnO H9nlL70N JUNE ll-m. 1973 NiRGfyin RIVtR ROCHESTER FIG. 40 continued. 269 Soenedesmus quadviaauda var. longispina (Chodat) G. M, Smith (Fig, 41). According to Skuja (1956) this taxon is most common in small ponds, and is rarely found in abundance in larger lakes. This is somewhat surprising since our observations would tend to indicate that it is common in the more eutrophied portions of the Laurentian Great Lakes. It has been recorded as being widely distributed in western Lake Erie (Tiffany 1934; Taft and Taft 1971). Soenedesmus quadrioauda var. maximus was listed from Irondequoit Bay of Lake Ontario (Tessler et al. 1953) and the nominate from stations in the open lake by Nalewajko (1966). Although not particularly abundant in our collections, this taxon is consistently present over a considerable part of the IFYGL sampling period. Only two isolated populations of S. quadrioauda var. tongisp-ina were noted in collections taken during the May 1972 sampling cruise. Both occurred at nearshore stations in the southeastern sector of the lake. In samples taken during the June cruise an increased number of occurren- ces were noted, still mostly at nearshore stations. Similar distribu- tion was noted in the July samples, with occurrences being restricted to stations nearest the south shore. In August populations of S. quadrioauda var. longispina occurred at most stations in the far eastern part of the lake, with isolated occurrences at stations along the northern shore and in the offshore waters. This species was much more generally distributed in our October samples although it still appeared at stations nearest shore or in the eastern part of the lake. Populations declined in the November samples with significant populations being largely restricted to offshore stations, although levels near those of the previous month were maintained at stations 8 and 19, near Toronto. Only a single population was noted in samples from the February cruise and this species was not recorded from samples taken during March. Isolated populations occurred in samples taken during April at stations nearest the southern shore, and the population density of S. quadrioauda var. longispina increased significantly in samples taken during June 1973 particularly from stations nearest the southern shore. Soenedesmus quadrioauda var. quadrispina (Chodat) G. M. Smith (Fig. 42). This entity is quite easily separated from the previous one on classical taxonomic characteristics, however, in light of the known plasticity of such characteristics under different culture conditions (Trainor and Hilton 1963; Trainor 1966; Trainor and Roskosky 1967) it is tempting to speculate that both may be ecophenes of the same genetic entity. The very limited distribution of 5. quadrioauda var. quadrispina might be interpreted as supporting such a supposition, but our observations do not furnish a plausible basis for resolving the question. In any case, the difference in distribution of the two morphological entities must reflect environmental differences at the stations sampled. No occurrences of 5. quadrioauda var. quadrispina were noted during the first two IFYGL biology-chemistry cruises. Limited populations were found in July at stations in opposite ends of the lake. In August, however, appreciable populations were found at most stations in the 270 TOBOfnO HF11ILTC3H NJBGPBfl RIVER MRT 15-19, 1972 ROCHESTER JUNE 12-16, 1972 TORONTO t^V^ HVILTON FIG. 41. HIPCPRfl RIVER ROGHESTER Distribution of Soenedesmus quadricauda var. longispina. 271 TOROKIO HFlMIUtW NIBGSRfl RIVER JULY 10-14, 1972 ROCHESTER TOROmO HWIUON RIVER RUGUST 21-24, 1972 ROCHESTER FIG. 41 continued. 272 TORONTO HPHILTON NIBGPftn RIVER OCT 30 - NOV 3, 1972 roOCSTEB TOfWJNTO HRfiiaot< NIBGfPfl RIVER NOV 27 - DEC 1. 1972 ROCHESTER FIG. 41 continued. 273 FEBRURRT 5-9, 1973 70KNI0 HPnlLTON «XjeSTEB MRRCH 19-22. 1973 TORDNTO HFWIUOH RIVER ROCHESTER FIG. 41 continued. 274 NRTULTON NIfiGFRfi RIVER RPRIL 24-28, 1973 ROCHESTER TORONTO «»»aTON NIFIGPRft RIVER JUNE 11-14. 1973 RODCSTER FIG. 41 continued. 275 HBMIUOM NlfiGflRfl JULY 10-14. 1972 ROCHESTER TORONTO HWIILTON RIVER RUGUST ROCHESTER FIG. 42 . Distribution of Soenedesmus quadriaauda var. quadrispina. 276 TORONTO HBWaON NJRGRRa WVEH OCT 30 - NOV 3. 1972 ROacsTER TOfWNTO HfiMIUON NlfiGflRfi RIVER NOV 27 - DEC 1. 1972 ROCHESTER FIG. 42 continued. 277 eastern half of the lake and at several nearshore stations in the western half. These populations were considerably reduced by October, and only isolated occurrences at stations near Toronto and Niagara were noted in November. No occurrences of this taxon were noted in months sampled subsequently. Ulothrvx spp. (Fig. 43). The dominant population included in this cate- gory is U. subconstrriata G. S. West (194 occurrences) although counts of two entities of uncertain taxonomic affinities (one with 63 occurrences and the other with 2) and a single record of U. tenerrima Kutz. have been included. Records of this genus in the phytoplankton of the Great Lakes are very incomplete, but personal observations indicate that high population densities are largely restricted to eutrophied regions. Nalewajko (1966) has recorded relatively low-level populations from Lake Ontario, although other authors do not record it among the more abundant forms in the phytoplankton. In the light of our results this is rather surprising. A few high levels of occurrence were recorded from samples taken during May 1972, but by June it was present in considerable quantities at most stations in the northern half of the lake and at several nearshore stations in the southern half. These populations apparently declined substantially by the time the July samples were taken, although substantial populations were still present at stations 8 and 19 near Toronto. Abundance of Ulothrix spp. increased again in August, particularly in the eastern and southern part of the lake. Extremely high population density was noted at station 60 near Rochester. Population densities declined in October and this trend continued through November, reaching the yearly low in February 1973. Samples from the March cruise showed slightly increased population densities of Ulothrix, but no further increase was evident in samples taken during April 1973. Populations did increase substantially in July but never approached the levels or the wide distribution noted in June 1972. Cyanophyta Anabaena flos-aquae (Lyngb.) Breb. (Fig. 44). Occasional low-level pop- ulations of this species are found throughout the Laurentian Great Lakes, but abundant occurrences seem to be restricted to areas which have under- gone some degree of eutrophication. It is one of the species which has become much more abundant in Lake Michigan in recent years although it was recorded as rare in earlier collections (Ahlstrom 1936). In Lake Ontario it was recorded from Irondequoit Bay (Tessler et al. 1953), and other records for the genus from the Bay of Quinte (Michalski 1968) and stations in the open lake (Nalewajko 1966) probably refer, in part, to this taxon. Ogawa (1969) found it to be abundant at a number of open lake stations sampled during September 1964. This species is capable of 278 mr 15-19, 1972 lomwio HfWILTON NIfiGfiRfl BIVEfl BOCHtSTEB TOBOrno HWIIUON NlfiOfifW ftlVER JUNE 12-16. 1972 ROCHESTER FIG. 43. Distribution of VlothHx spp. 279 TORONTO HRHILTON Nincmn WVEP JULY 10-m. 1972 ROCHESTER MflfllLTON NIflGfW) RIVER AUGUST 21-214, 1972 ROCHESTER FIG. 43 continued. 280 TORtKTO C^V^ HffllUON OCT 30 - NOV 3. 1972 WVER 200.00 BOCHESTEft Towmo HailUOM PIVER NOV 27 - DEC 1. 1972 ROCttSTCR FIG. 43 continued. 281 TOnONTQ [WILTON NJfiGmfl FEBRUflRT 5-9, 1973 WKHESlEfs TOfwno HflRCH 19-22. 1973 uBiiaoN ROCtCSTtR FIG. 43 continued. 282 APRIL 2^1-28. 1973 TORONTO MWIItTON NIflGflRfl WVEB NJCHESTEfi TORONTO JUNE 11-114, 1973 HfiMILTON NlflGflRfl RIVER ROCHESTER FIG. 43 continued. 283 lORomo i«iiL7a BlVEn JUNE 12-16. 1972 BOCHESTER TOBDKIO HRMILICW RIVER JULY 10-14. 1972 RODIESTEH FIG. 44. Distribution of Anabaena flos-aquae. 284 lORCNID RUGUST 21-211, 1972 ROCfCSTER lOfUKTO KlrtlUCN OCT 30 - NOV 3, 1972 filVER R0OCS7EB FIG. 44 continued, 285 producing obnoxious water blooms and is one of the taxa contributing to such nusiances in western Lake Erie (Ogawa and Carr 1969). On the basis of Ogawa and Carr's study, it would appear that this species is also one of those capable of fixing nitrogen under conditions where excessive phosphorus input led to depletion of available nitrogen in the system. This species was not noted in samples from the May 1972 cruise, and only a few isolated populations were noted in the June samples. It was found in considerable abundance at a number of stations in the eastern part of the lake during July. In August it was particularly abundant at station 90 near Oswego and at several stations near Niagara. Somewhat smaller population densities were noted at several stations in the eastern part of the lake and at isolated nearshore stations along the northern shore. Only a few isolated populations were found in samples from the October cruise, and this species was not recorded from any of the subsequent cruises. ATtabaena variabilis Kutz. (Fig. 45). The identity of this small species of Anabaena is somewhat questionable. Although it is apparently very widely distributed in both fresh and saline water (Huber-Pestalozzi 1938), previous records from the Laurentian Great Lakes are lacking. It forms gas vacuoles and may contribute to water blooms, and Ogawa and Carr (1969) have demonstrated that laboratory strains of this species are capable of fixing nitrogen. A single isolated population was noted in collections taken during the May 1972 cruise, but it was not noted in June and July. In August, however, high population densities of this species were noted at a number of stations in the southern half of the lake and less abundant occurrences at several stations nearest the northern shore. A few isolated occurrences were found in samples from the October and November 1972 cruises and February 1973 cruises. This species was not found in samples from the March and April cruises but it did occur at a few stations in the eastern half of the lake during June 1973. Anaaystis cyanea Dr. and Daily (Fig. 46). This species is one of the blue-green algae capable of forming nusiance-producing water blooms. It is present in many highly eutrophied areas in the Great Lakes, but reliable quantitative estimates of its abundance are not common. This is partially because it tends to occur in ephemeral blooms and the cells usually are contained in large colonies, which renders obtaining accu- rate estimates of its abundance very difficult. Like most bloom forming species of blue-green algae. A, cyanea usually reaches its peak abundance during the warmest months of the year. In this respect, its seasonal distribution in Lake Ontario during the IFYGL sampling period is highly unusual. In May 1972 a single isolated population was noted at station 90 near Oswego. In June somewhat higher 286 TOROKTO HIRGPRfl RJVEB MnY 15-19, 1972 BOOCSTEK TORONTO HRMRTON RUGUST 21-214. 1972 fWQCSTER FIG. 45. Distribution of Anabaena varidbilis . 1?,1 OCT 30 - NOV 3. 1972 1W0WTO HRMILIOK MRGPfW fiJVEB K)0€STER NOV 27 - DEC 1. 1972 lofwno HRfiiuav RIVTR BIXJESTER FIG. 45 continued. 288 "roWKTO tpraun* WBOffsa fUVER FEBRURRT 5-9. 1973 roacsTth TOROKTD Hff.JUOM BlYOl JUNE 11-lU. 1973 KJOeSTER FIG. 45 continued, 289 TOBONTO HflMILTi filVLfl MAT 15-19. 1972 ROCHESIEfi TOflOMTO HfiMILTOfJ JUNE 12-16. 1972 BOCHCSTER FIG. 46. Distribution of Anacystis cyanea. 290 TOBOKTO HfiMFLTON RIVEfl JULY 10-14, 1972 BOCMESTEB TORONTO HfWILTOfl NlRGfl.'W RIVtfl AUGUST 21-24, 1972 ROCHESTER FIG. 46 continued, 291 OCT 30 - NOV 3. 1972 TOfiOHTO NIRJfiHfl RIVER fiOCfCSTEfi TORONTO HfWILTOfJ RIVER NOV 27 - DEC 1. 1972 R0CHE3TEB FIG. 46 continued. 292 TORWnO HfiKIUi NIBCfVW RIVER FEBRUARY 5-9, 1973 fWaCSTEfi TOBOwro MflMILTi NIfCftRfl BI/ER MARCH 19-22, 1973 ROCtCSTEH FIG. 46 continued, 293 TOBOKTO Hfl«rLT«. NIRCflFlfl RIVER flPRIL 2Lt-28, 1973 ROCHESTER TOROKIO HfiMILl RIVER JUNE 11-114. 1973 nOCSCSTER FIG. 46 continued. 294 populations were noted at the same station, at station 85 adjacent to it, and at station 10 in the far end of the lake. In July a single population was detected at station 3, and in August, when population densities might be expected to be relatively high, this species was not noted in any of our samples. In October, however, high population densities of A. ayanea were noted at a number of stations. By November populations had declined except at stations 72 and 73, east of Rochester. Only single isolated populations were noted during February, March, and June sampling periods in 1973. Anaaystis inaerta Dr. and Daily (Fig. 47). This small species contains gas vacuoles and, according to Drouet and Daily (1956), may form blooms. It is, however, rarely associated with nuisance conditions in the Great jLakes. Unlike many other species of blue-green algae in the Great Lakes it tends to reach peak abundance during cooler months of the year, es- pecially during the fall cooling period. In reviewing the records of its occurrence available to us, it would appear that it is most successful under conditions where silica depletion limits diatom growth. In Lake Ontario during the IFYGL field sampling period it was abundant at stations in the eastern part of the lake in I^Iay, with only isolated low-level populations being detected at other stations. During the June sampling cruise, conversely, sizable populations were found only at stations in the far western part of the lake with a few low-level occurrences at mid-lake stations and in Mexico Bay. Populations dropped to very low levels during the July sampling period, but a few isolated abundant occurrences were noted at widely separated stations during August 1972. Only occasional occurrences were noted during the rest of the months sampled, and it did not return to the levels of abundance noted the previous spring. Aphanizomenon flos-aquae (L.) Ralfs (Fig. 48). This species is capable of causing extreme nuisances under bloom conditions. Its distribution in the Laurentian Great Lakes is largely restricted to highly eutrophied areas. Although it is a conspicuous element of net collections from such areas, estimates of its abundance made by standard phytoplankton counting methods are subject to large uncertainties because of its growth habit. It has been reported as being abundant in Irondequoit Bay (Tressler et al. 1953) and the Bay of Quinte (McCombie 1967; Michalski 1968) but, although it is visibly present in the surface waters of some regions of Lake Ontario proper, it has not often been reported from stations in the open lake. Ogawa (1969), however, found it to be abundant at a number of stations sampled in September 1964. In our collections a single occurrence was noted at station 105 in Mexico Bay during June 1972, and relatively high abundance of this species was noted at this station and a few others in the eastern part of the lake during August. Scattered populations were also noted in samples taken during October, but this species was apparently absent from subsequent samples. 295 MAT 15~L9. 1972 TORONTO HflKILTaJ NIBGflRfl BIVfEfi BOCHESTER TORONTO Hfl«ILTO,-> BIVEfl JUNE 12-16, 1972 ROCHESTER FIG. 47. Distribution of Anaaystis inaerta. 296 HBHTLTi NIBGfiRfl ftlVEfl JULY 10-14.. 1972 ROCHESTER TORONTO rtWILTi NIBGflfifl RIVER AUGUST 21-2Lt, 1972 ROCHESTER FIG. 47 continued. 297 TOBOKtO mm^ HlfiCflfW tUVEB OCT 30 - NOV 3. 1972 BOCtESTEB TORONTO WWIl-TOi' BlVcfl 27 - DEC 1 . 1972 600.00 BOCHESTEfl FXG. A7 continued. 298 TORONTO HflrtlLTl RIVEfi FEBRURRT 5^9, 1973 BOCHESTEB TORONTO KailLTON NIRGBTifl BIVDJ MfiRCH 19-22. 1973 ROOIESTEfi FIG. 47 continued 299 RPRIL 24-28, 1973 icmmo HfiHILTl NlftGRRfl RIVEfl BOCHESTEfl TOflONTO JUNE U-itl, 1973 HR-IIUOi RIVtfi FOQCSTEfl FIG. 47 continued. 300 TORCWIO RJV£R J.UNE 12-16, 1972 RooesTEn TORONTO JULY 10-m. 1972 HFMIUON Rivm KXJCSTEB FIG. 48. Distribution of Aphanizomenon flos-aquae. 301 •roRcmo naiiLia NlKffJi RIVER RUGUST 21-24. 1972 BOCHtSIER TORONTO Hfwium HIRSTS RiVDH OCT 30 - NOV 3. 1972 ROOtSlER FIG. 48 continued. 302 Gomphosphaerla aponina Kutz. (Fig, 49). According to Huber-Pestalozzi (1938) this species is a facultatively planktonic form which is widely distributed in large and small lakes and also occasionally occurs in brackish water. Although records are insufficient to assess its general distribution in the Laurentian Great Lakes, it has been reported from western Lake Erie (Taft and Taft 1971) and we have observed occasional populations in Lake Michigan. Tlie occurrence of G. aponina in Lake Ontario during the IFYGL sampling period was strikingly limited. It was noted only in samples from the October 1972 cruise when relatively high population densities were noted at several stations in the eastern part of the lake. Gomphosphaeria lacustris Chodat (Fig. 50). This very common and widely distributed member of the genus is found throughout the Laurentian Great Lakes and is often one of the more abundant species of the sparse sinmuer plankton of the upper lakes. Although it was recorded from stations in Lake Ontario collected in September 1964 by Ogawa (1969), it was not reported in more recent surveys. In our collections, a single population was noted from samples collected during May 1972. It was not found in samples taken during June and July, but was relatively abundant at scattered stations collected during August. Similar occurrences were found in October, but it was absent from collections taken on subsequent cruises until June 1973, when a few isolated populations were again collected. Gomphosphaeria wickurae Dr. and Daily (Fig. 51). According to Drouet and Daily (1956), this species often forms conspicuous blooms during the warmer months of the year in freshwater lakes. Partially because of the confusion that surrounds the taxonomy of this species, previous records of its occurrence in Lake Ontario and the other Great Lakes are difficult to determine. It would appear, however, that it is usually associated with eutrophic conditions and is potentially a nuisance- producing form. In our samples, only isolated low-level populations were detected during May through August 1972. In October, however, large populations were noted at most offshore stations in the northwestern sector of the lake and at a few stations in other regions. Although populations were somewhat reduced in samples from the November cruise, they were again noted at many stations, primarily in the western portion of the lake. A few stations sampled during February 1973 still contained significant levels of this species, but it continued to decline in abundance and only isolated occurrences were noted in March and April. It was not noted in our June 1973 samples. Osaillatovia limnetica Lemm. (Fig. 52). This species is by far the 303 OCT 30 - NOV 3, 1972 TO!«»no HflfilLTOlJ NIflGa=1R BIVER ROOeSTER FIG. 49. Distribution of Gomphosphaeria aponina. most common member of the genus in our collections. According to Huber- Pestalozzi (1938) it is a common euplanktonic form which often occurs in polluted water. It apparently has not been widely reported from the Great Lakes, although Munawar and Nauwerck (1971) record it as being an abundant form in the fall plankton of Lake Ontario, and Nalewajko (1966) lists several occurrences of the very similar 0. planktonica Wol., also from Lake Ontario. Relatively small populations of this species were noted in our collec- tions from the May 1972 cruise. In June, however, it was one of the dominant species at many stations in the northern part of the lake. The very abundant populations noted the previous month had declined by July, although there was one particularly high abundance occurrence noted at station 19 near Toronto, and the species was quite uniformly distributed throughout the lake. There was, however, a trend towards lower population densities at offshore stations in the southern half of the lake, a pattern which was repeated by several other taxa. Relatively low population densities were noted at stations sampled during August, with a tendency for highest abundance to occur at stations along the southern shore. Population densities were also low during October, but populations seemed to be evenly distributed 304 JKWro KWILTW RIVER MAY 15-19, 1972 BOQCSItB TOBOffTO tflNlUOt AUGUST 21-24. 1972 BoaesiEB FIG. 50. Distribution of Gomphosphaeria laaustris'. 305 TOWtno KaMILTW ftlVEB OCT 30 - NOV 3, 1972 pooEsicn TOEWIO JUNE 11-m. 1973 tftFf« RIVER 1200.00 ROCHESTER TORONTO NIBGOm RIVtB fiUGUST 21-2"4. 1972 1200.00 ROCHESTEB FIG. 56 continued. 335 TORONTO HflnrLTON NIRGCfW RIVER OCT 30 - NOV 3. 1972 BOOCSTEB TORONTO HflHILTON HlfiGRRfl WVEfl NOV 27 - DEC 1. 1972 1200.00 ROCHESTER FIG. 56 continued. 336 TORONTO HflMILTOT) NIfiGfif« RIVEO FEBRURRT 5-9. 1973 1200.00 BOCMESTER T(]B0NTO HfiMILTOH NlBGfifW RIVER MRRCH 19-22. 1973 1200.00 ROCHESTER FIG. 56 continued. 337 TORONTO HRWaON RIVER RPRIL 24-28. 1973 1200.00 ROCHESTER WMILTCN HIBGfRfl RIVER JUNE n-m, 1973 ROCHESTER FIG. 56 continued, 338 than 10 ym in largest dimension. Identification of preserved specimens of these organisms is exceedingly difficult, and the species occurring In the Great Lakes phytoplankton have been, historically, very poorly treated. Although reliable published records are lacking, our obser- vations indicate that organisms in this group are relatively much more iniportant in the Lake Ontario system than they are in the upper Great Lakes. The most abundant organisms in this class occurring in our collections were Chlamydomonas spp, (probably including zoospores of other chlorophycean species), Chrysoahromulina paiva Lackey, Pedinomonas spp., and Rhodomonas spp., although less abundant populations of other cfirysophycean flagellates were present at many stations. As Munawar and Nauwerck (1971) noted, Rhodomonas was present during all seasons and its abundance seemed to follow the general trends of total phyto- plankton abundance. In our collections Chrysochromulina was most abundant in June and July, with a minor peak in populations in the fall, Chlamydomonas spp. appeared to have a similar seasonal succession although they tended to become abundant somewhat later and abundance peaks were similar to other chlorophycean species. Although Munawar and Nauwerck Indicated that Pedinomonas was primarily a summer form, in our collections it became abundant at nearshore stations in the early spring and reached peak abundance at open-lake stations in June. This is not surprising, in that Huber-Pestalozzi (1961) indicates that P. mi-nutissima Skuja, which is probably the main species involved, is a cold stenotherm. Microf lagellates were abundant at the shallower stations during the May 1971 cruise, and high population densities were noted at stations in many parts of the lake during June. In this month, howeyer, there was a consistent pattern of low population densities ait stations nearest shore in the western part of the lake between Niagara and West Point and at offshore stations in the southern half of the lake. Appreciable populations of microf lagellates were still present in July, but peak abundances were down considerably from June values;. At this time highest population density occurred at station 14 near Niagara. Population levels of microflagellates were further reduced in August and only rcilatively low population densities were found throughout the lake. Average abundance of this group increased somewhat in October samples, but was low in November and remained low during February and March 1973 cruises. A general increase in abundance of the group was noted in the April samples, and notably increased densities occurred at several stations in the eastern part of the lake. An extreme bloom of these organisms apparently occurred at the time the June 1973 samples were taken, and abundance in excess of 5000 cells/ml were noted at several offshore stations. Highest abundances at this time substantially es:ceeded any found during 1972. Vertioal Distribution of Phytoplankton at Master Stations In the following sections, data are given on the vertical trends in total phytoplankton abundance and the abundance of major groups at different 339 seasons. Data are derived from standard sampling depths at the master stations. In general, these data are relatively well correlated with trends in chlorophyll concentration (Table 6), and particle counts (Table 7) both for total phytoplankton and for particular groups during their maximum growth phase, and relatively poorly correlated during periods of decline. The vertical distribution of total phytoplankton cell counts at master stations is shown in Figure 57. Open lake stations sampled during May had relatively low and uniform counts at all depths, with a slight increase in the 20 m sample from station 24. Cell densities were considerably higher at station 96, but no stratification of cell densities was evident. In June, cell densities were still low and uniform at stations 45 and 75 and somewhat higher but still uniform with depth at station 10. At station 24, however, very large values were found in samples from the top 15 m, and samples from the lower depths had higher counts than all stations except station 96. In July, stations 24, 45, and 75 in the central part of the lake had relatively high counts in the epilimnion, with peak values occurring at 5, 10, and 15 m. Station 10, in the western end of the lake, and station 96, in the eastern end both had lower and more vertically uniform phytoplank- ton counts. In August, cell counts were considerably reduced at the open-lake stations, with peak values occurring in the top 10 m. At station 95, on the other hand, phytoplankton density increased from levels noted the previous month, with especially large values present in the 5 and 10 m samples. By October less pronounced stratification was evident and cell counts were relatively low and irregular, even at station 96. Abundance continued to decrease at the main-lake stations sampled during November, but remained near levels noted the previous month at station 96. Phytoplankton densities were low and uniform at all stations sampled during February, and only slight increases were noted at the main lake stations during March although a large increase was found at station 96. Approximately the same situation was present in April, although slight increases were noted at stations 10 and 24 and values continued to increase at station 96. By June 197 3 values had increased greatly at all stations sampled, and phytoplankton densities were strongly stratified at all stations. Peak values occurred at 5 or 10 m depths and the anomolous 30 m peak noted in the cholorophyll results were evident from the counts. The vertical trends in abundance of the major phytoplankton groups at the master stations sampled are shown in Figures 58-61. The diatoms (Fig. 5 8) were the most consistently abundant at the master stations. In May, large populations were present at all depths sampled at station 96, with largest concentrations occurring in the near-bottom waters. Abundance was much lower at stations 24 and 75 and more evenly distributed with depth, although there was a noticeable concentration at the 20 m depth at station 24. In June, largest populations were 340 TABLE 6. Correlation between fluorometrically determined chlorophyll a values and cell counts in total and by category at master stations. Total cells Macrofla- Blue- ml gellates greens Greens Diatoms R(a.99 May .8301 .9388 .6009 -.0464 .5409 .5256 June .8875 .7924 .6715 .5350 .8508 .3801 July .6703 .6309 .2409 -.2323 .4507 .3683 Aug. .6285 .4297 .4858 .4960 ,0568 .3646 Oct. .6258 .6897 .3809 .2635 .5475 .3575 Nov. .8169 .8301 .2253 .4017 .9218 .4128 Feb. -.1367 -.2383 . 0155 -.1895 -.1396 .4076 Mar. . 9584 .4338 .0027 .1425 .9660 .4487 April' . 9129 .8506 .2920 -.0028 .9051 .3542 June .8090 .7416 .2130 .0419 .7395 .3646 TABLE 7. Correlation of particle counts in channels measured with cell counts as determined by visual identification for master stations. Particle Count Channels 5-lOym 10-20ym 20-40ym 40-80ym 80-150um 5-150ym R(a.99 MAY Total cells/ml .7741 Microflagellates .7635 Blue-green .2499 Green -.2156 Diatoms .6764 JUNE Total cells/ml .7285 Microflagellates .7025 Blue-green .5585 Green .3683 Diatoms .6711 ,7457 .6633 .4938 -.0031 .7594 .8502 .8702 ,7604 .0996 .8345 .2475 .2267 ,1266 -.1237 ,2544 .1874 -.2019 -.1466 .2030 -.2118 .6300 .5086 .3196 -.0842 .6609 .7229 .2886 .3634 ,5785 .7396 .6529 .2273 .3830 .7020 .6963 .4799 .2137 .2934 ,6119 .5447 .3099 .0915 .1618 .3960 .3531 .7183 .3159 .3268 .4022 .7006 .4705 .3646 341 TABLE 7 continued. Particle Count Channels 5-lOym 10-20yra 20-40pm 40-80ym 80-150iim 5-150ym R@.99 JULY Total cells/ml .5348 Microflagellates .5945 Blue-green .2602 Green -.3168 Diatoms .2670 .7348 .6425 .2366 .0492 .5976 .7318 .7234 .4296 .2380 .6461 .2267 .0668 .0305 -.0129 .2559 .2469 -.3000 -.3611 -.3174 -.3110 .4458 .3298 -.0150 -.1180 .3157 .3646 AUGUST Total cells/ml .3829 Microflagellates .5088 Blue-green .1658 Green .2100 Diatoms -.1235 .5539 .5877 .4515 .3566 .4315 .5852 .2088 .2040 .5857 .5274 .2695 .5726 .4208 .0753 .2061 .3640 .5490 .3935 .1242 .2594 .0850 .0993 .0639 -.0616 -.1108 .3646 OCTOBER Total cells/ml .2728 Microflagellates .2417 Blue-green .2185 Green -.0448 Diatoms .2871 .3629 .3697 .2857 .2720 .2987 .3114 .3122 .2080 .1270 .2620 .2550 ,2432 .1726 .0979 .2302 .0900 .1451 .2111 .4817 -.0117 .3794 .3946 .3099 .3850 .3141 .3683 NOVEMBER Total cells/ml .7016 Microflagellates .6825 Blue-green .1852 Green .2214 Diatoms .8451 .7864 .7663 .7321 .3292 .7447 .7546 .7259 .6820 .3010 .7195 .2525 .2580 .2633 .0963 .2151 .3229 .3366 .3312 .2367 .2660 .8974 .8618 .8155 .3709 .8765 ,4128 FEBRUARY no significant correlation 342 TABLE 7 continued. Particle Count Channels 5-lOym 10-20ym 20-40ym 40-80nm 80~150ym 5-150ym R(a.99 MARCH Total cells/ml .7902 Microflagellates .4044 Biue-greem .1572 Green . 1607 Diatoms .7859 .9153 .9235 .8723 .1203 ,8594 .3124 .2550 .3094 .0285 ,3851 .0675 .0561 .1074 -0336 .1324 .1080 .0908 .0205 -.1611 .1447 .9252 .9370 .8821 .1308 .8599 .3978 APRIL Total cells/ml .3377 Microflagellates .1600 Blue-green . 2735 Green -.2955 Diatoitts .3604 .6315 .7988 .3606 .0484 .5265 . 5214 .7264 .3448 . 0810 .3669 .2678 .2139 .0735 -.0007 .2908 .0203 .0195 .1111 .1912 -.1937 .6319 .7951 .3513 . 0342 .5407 ,3542 JUNE Total cells/ml ,5649 .7377 Microflagellates .4940 .7240 Blue-green .3517 .1963 Green .2305 -.0226 Diatoms .2918 .6295 .7200 .7507 .6478 .6476 .6280 .7013 .6354 .5836 .1364 .2331 .2214 .3336 .0613 -.0383 .0179 .1795 .8430 .7275 .3852 .4073 .3683 found at station 24, which had an extreme peak at the 15 m sample depth. Relatively high numbers were present at the surface of station 10, but declined below. Stations 45 and 75 had lower and more vertically uniform abundances of diatoms, although there was a concentration in the near- bottom sample from station 75. Populations at station 96 were reduced from the levels noted the previous month, but the trend towards highest concentrations in the near-bottom waters was still evident. In July, abundance of diatoms was notably reduced at all depths sampled at station 343 KXM Of— I > I SO 200 10 Mnr 15-19, 1972 sooo -t — I — I- 6000 -i 1 K tooo t I I 24 «45 75 «000 1 1 1 I 96 «000 IT § / 200 ' 10 JUNE 12-16, 1972 8000 r-» 1 K 6000 •15 75 woo 96 eooo jL so 2004- y 10 JULY 10-14. 1972 eooo I < t — I- ^ 75 <000 I I I 96 FIG. 57. Vertical distribution of total phytoplankton cell counts at master stations. 34A RUGUST 21-24, 1972 9000 ■4 1 ■+■ se- s«el MOO tOM 7 i us 75 -fcr-l *- 96 OCT 30 - NOV 3. 1972 ■4 1 ►- tioo rl 1 »- Wit 904 aeo- -i — I — I- 10 2y «5 75 «M0 H 1 1- 96 NOV 27 - DEC 1. 1972 S 9000 tOBO Sir — I— « — t- n — •- — » t- g se «4SA H 1 h iM 10 24 tool H 1 h. 45 75 «ooa H 1 1- 96 riG„ 57 continued. 345 & sooo «!—« ' *■ SO 2004 10 FEBRURRT 5-9, 1973 eooo -» — I — t- tooo I I I 1 > »■ t 214 45 75 sooo -I — I — I- ., 96 eooo Q- — I — I — t- -.so- I 200" 10 MRRCH 19-22, 1973 esoo I t H eooo 211 I 8000 ■H 1— — t- 145 75 tooo .. 96 «000 8[-j— 1 — I 1- SCO 10 APRIL 24-28, 1973 tooo -I H — I- ^ 2U «000 .1 145 «000 » I — t- 75 tooo -« — 4 *- <^ 96 FIG. 57 continued, 346 JUNE 11-14, 1973 eooo «000 r 75 FIG. 57 continued. 96 and near the surface at station 10, but remained relatively high at lower depths. Station 24 had similarly low surface values, but a distinct peak at 15 m. Station 45 had a similar peak at 15 m, but the surface values were larger than at station 24. Station 75 had relatively high surface values also and highest concentrations at 5 m. Samples from August and October showed relatively low abundance of diatoms and relatively uniform abundance at all depths sampled, although there was a slight increase in abundance at all depths sampled at station 96 in October. In November there was a significant increase in abundance of this group at all depths sampled at station 96, but numbers remained low and vertically uniform at the other stations. In February, abundance of diatoms was low throughout the water colximn at all stations sampled . In March a slight increase was noted at most depths sampled at the main lake stations and very high numbers were present at station 96, with peak abundance occurring in the near-bottom samples. Abundance of diatoms continued to increase at the main lake stations sampled during the April cruise but remained relatively uniform throughout the water column. Abundance remained very high at all depths sampled at station 96. In June 1973 abundance of diatoms was considerably reduced at station 95, although distribution through the water colimin remained fairly uniform. Numbers increased at the offshore stations with peak abundance occurring at 10 or 15 m depth, except at station 75, where highest abundance was noted in the surface sample. The abundance of green algae (Fig. 59) was more seasonal than that of the diatoms, and during most months they were a quantitatively less important part of the total phytoplankton assemblage. Samples from the May 1972 cruise showed relatively low numbers of green algae and uniform distribu- tion throughout the water column. In June, numbers of green algae increased 347 MAT 15-19. 1972 p qooo Oi — I — I — I — ►• i ■ SO e qooo r* — I — I — »- 200 / 10 1000 uooo -i — I — t — »• I I t > ) t 24 1 45 lUOO -H — I — I— ♦• 75 96 JUNE 12-16. 1972 9 4000 tl t . 1 — I — ►• 14/ <1000 -»— I — t K 200 10 11900 -t — I — ►- ^ <1000 -^ — I — i- ^ \ 75 96 JULY 10-14. 1972 «000 so r™ g ii 4000 ■H — I — I 1- 200 10 4000 -\ — I— ♦- 24 45 4000 ■+— t — I — »- I 96 FIG. 58. Vertical distribution of diatoms at master stations. 348 RUGUST 21-24, 1972 t (toco ±50- M too- HOOO -»— I — I — f- 10 uooo -1 — I — I — t- ^ 24 woo I I -1 — ►• 45 75 «ooo -I — I — I — ►- 96 OCT 30 - NOV 3, 1972 t HOOO |— « — I — I — ►■ g ■ so 200' MOOD -»— ( — (— t- 10 24 uooo -» — I — I — l- 11009 H — I — I — I- 45 75 HOOO I I ) — ►• 96 NOV 27 - DEC 1, 1972 t «000 8 k ' ' ' ► iso. 200" 10 ilOOO H 1 h— *- 24 HOOO -) — I — I h HOOO > I -i — t- ^ 45 75 HDOO -I — I — I — K 96 FIG. 58 continued, 349 D >(000 Oj— I — *—* — >- ± 50- 200 10 FEBRURRT 5-9. 1973 IBM -« — *—* — •- 2H HDDO ■+— ( — ►— V ns 1(000 H — I — » — f- 75 itOOO 96 4000 Op-1 — 1—1 — »- SO 200 10 MRRCH 19-22, 1973 IICOO -»— t — I — t- < 4000 H 1 1 ►- 24 45 4000 -t — I — I — t- 75 4000 -t — tr-H ►- e 96 g 4000 i 50 i 200" 10 APRIL 24-28, 1973 40OO -i — I — I — K 4000 i 24 \ 45 4000 -t — I — t- 75 4000 -I— t lv-«- \ 96 FIG. 58 continued. 350 JUNE 11-14. 1973 rt — *—* — •- i .1 us tT"* HDOO " 4- 75 «000 H — I — •— ♦■ 96 FIG. 58 continued. significantly although vertical distribution of populations was very irregular. The major contributor during this month was Saenedesmus hiaettu'laj'-ts . Samples from July showed reduced nximbers and most signifi- cant concentrations occurred below 10 m depth. In August there was a large increase in the abundance of this group at stations 10, 24, and 96 and there appeared to be a significant concentration of populations at 10-20 m depth at these stations. Numbers were lower and less vertically stratified at stations 45 and 75. By October, abundance of this group had ■been reduced to very low levels except at station 96, and remained an in- significant part of the assemblage at all stations sampled during November 1972 and February and I-Iarch 1973. In April a slight increase occurred at most stations and depths sampled. In June, very high abundance was found in the 10 and 15 m samples from station 96. At the other stations sampled numbers remained relatively low, but subsurface peaks were evident. Compared to the other groups, the blue-green algae (Fig. 60) constituted a relatively small part of the phytoplankton assemblage in most samples from the master stations. Small surface concentrations were noted at station 96 in May and at stations 10, 24, and 96 in June. In July, highest concentrations of these organisms occurred below 10 m at stations 24 and 96. The highest concentrations noted during this study were found in samples from the upper 10 m at station 96 during the August cruise. By October relatively low levels of blue-green algae were found at all stations and depths sampled. Although numbers were further reduced, populations were noted at most stations and depths during November. In February, March and April 1973 this group was mostly represented by low- level populations of OscLltatoria spp. occurring at depth. During the June 1973 cruise some increase in the abundance of this group was noted at station 96 and in the surface samples from station 24. 351 P HOOO Oj— I — I — »— »- e ioO' 10 MAY 15-19. 1972 IIOOO I t I I 4000 U)00 I I I — t- r 1 ' ' I — ►- rr-t — I — *—*• i 2«4 •45 75 I 96 MOOO JUNE 12-16. 1972 lUOO -t-rt — I— v IIOOO lilt- : ^ 4000 ■ I I I >■ 24 US 75 ■UMO r« — t — t— »- 96 woo L » « ' ' ise- It 200 10 JULY 10-14. 1972 4000 IMOO -t — I — I— •- I I I I — H ) qooo 2H 115 75 4000 -I — t— t — K 1 95 FIG. 59. Vertical distribution of green algae at master stations. 352 lUGUST 21-24. 1972 voao -» — I — ►- vooo ti l l y ttOOO « — t— I — *- m U5 75 tlOOO 96 OCT 30 - NOV 3. 1972 9 ■ HOOO -1—1 — »- UDOO -t — ) — ( — \- 8 2: 50^ I 10 2U U5 75 4000 -+— I — t— »- 96 NOV 27 - DEC 1. 1972 @ 4000 9j— t — I — I — t- 4000 -♦— t 1 K 4000 -♦—I — I — »- ul 5 so 200 10 2i| 4000 -» — t — I — I- ii5 75 4000 -t— » — I — »- 96 FIG, 59 continued. 353 KOOO t) — I — I — t — I- 30- 200- 10 FEBRUnRY 5-9. 1973 I MOOO -I — I — I — »- 24 HOW -t — I — I — k- 45 uooo -t — I — t- 75 IIOCO 96 9 UOOO O i I > I — I- 90' I' 800' ' 10 MRRCH 19-22. 1973 <• UOOO -t 1 « !■ 24 «000 -• — t - I »■ 45 4000 -t— 1 — I — t- 75 1)000 -t — • — I — K 96 HOOO 01 — I — t— « — (- g 90 ^ 800 10 nPRIL 24-28. 1973 UOOO -« — I— -t — »- 24 4000 45 UOOO -t — I — I — ►- 75 UOOO -I — » — *— ♦- 96 FIG. 59 continued. 354 so- 200 IIODO ■• — t — I — t- 10 JUNE 11-14. 1973 \ ucoo -« — I — I H i 24 <10CO -i — I — I — *- 45 ilOOO ■M— I — I— +- 75 FIG. 59 continued. As; might be expected, the vertical distribution of microf lagellates (Fig. 61) was somewhat more restricted, especially during the summer months, than the other major groups of phytoplankton. In May relatively high numbers of organisms in this group were noted at station 96, but other stations had significantly lesser numbers. By June 1972 abundance was present in 5 m samples from stations 24 and 96 but numbers remained relatively low at other stations and depths sampled. During the July cruise high abundance was noted at the 10 m depth of station 24 and at 5 and 10 m samples from station 45. Somewhat smaller concentrations were found at 5 and 10 m depths at the other stations. In August highest concentrations occurred in the 5 m samples from stations 10 and 24. Some- what smaller niombers were noted at 10 m at station 45 and 5 m from stations 75 and 96. By October, numbers of this group had been reduced and abundance was more uniformly distributed throughout the water column. Numbers were vertically uniform and relatively low at all stations sampled during November 1972, except station 96 where numbers were somewhat larger. Abundance of this group was low at all stations and depths sampled during February 1973, and only slight increases were noted in March samples. In April there was some increase at station 96, but numbers remained low at other stations sampled. During June 1973 relatively high numbers of microf lagellates were noted in all samples from the top 20 m at all main lake stations, but considerably lower numbers were present at station 96. A notable secondary peak in abundance occurred in the 30 m sample from station 45. 355 1(000 Op-« — I — I — •- m 10 MRY 15-19, 1972 HOOO MOOO 24 45 uooo 75 -* — I— « — »- 96 D UOOO t tf « « ' ■*- so 200 10 JUNE 12-^16. 1972 1 UOOO -• — ►— 1 — t- 24 HOOO H 1 (— +- 96 9 1000 ± so 200 ' ,' 10 JULY 10-14, 1972 uooo uooo 4000 -I 1 1 1- (—* 1 • ►• 1—1 ►— I k- ,' 24 ,^ 45 r* 75 <(000 -»— I — t — »- < 96 FIG. 60. Vertical distribution of blue-green algae at master stations. 356 fiUGUST 21-211, 1972 tl&OO H — ) — t — i- HCK» I I I — f- HODO -« — I — ¥—*• ± sol -t — I — I — •- 10 2 I — < — »- %0OS ttOOO H — I — i- r—i — I— I 1- S04 2004 10 2U 45 I 1^ 75 lUOO ■t > I t :) 96 FIG. 60 continued. 357 SO' 200 10 FEBRURRY 5-9, 1973 11000 vooo of— t — I — I — »- I — I — »— t — t- itOOO liOOO 1000 I I t ! ■ I t I t I — I — I — 1 — *• 24 «15 75 96 4000 8 ' ' ' ' I 300 10 MRRCH 19-22. 1973 UOOO HOOO -i — I — t — f I — I — I — I — »- 214 U5 1000 -I — I — I — K 1' 75 1000 -I — •— t — ^^ ^ 96 1000 fr—i — I — I — *• £ 90 200 10 RPRIL 24-28. 1973 1000 -i — I — I — t- 24 1000 I I I > <* 45 1000 -I — < I I 75 1000 96 FIG. 60 continued. 358 JUNE 11-111. 1973 S twos 9« > I I I I I < t a I I > I » .^ ? 10 214 ns %soo • ■ I ♦ I > .' 75 woe t > > »■ t 96 FIG. 60 continued. r-«— »— I — I- se ? ;!S9- 10 MRY 15-19. 1972 ■ t I I — t- -1 — I — »— +- g — •— I — ►— »- 2!4 «i5 75 use I . I I !■ 96 IIDOO -» — 1 — I — I- < ■ 20O' 10 JUNE 12-16, 1972 UOM 45 HODO H — •— I — t- 75 Hoe» r< 1 >■ ♦- 95 FIG. 61. Vertical distribution of microflagellates at master stations. 359 ) ^» IM «M0 < t I > ■ 10 JULY 10-14. 1972 t' 2U wot F •15 MOM < — I t ■♦• 75 HOOB I I I >• 96 9 «tSM 200 10 AUGUST 21-24, 1972 tooo itOOO .. < I — I — t- r— t — I — I — t- r- 7 V f V . 2y .. 115 ■1000 7S .1 «l>00 -+— » — t—t- 96 OCT 30 - NOV 3, 1972 t HOOO r « i — 1 — H 200 MOOD -t— » — I — t- 10 < .24 45 ■ISOD -♦— t — I — I- 1' HOOO -t— « — I — t- 75 ■ 2y HOOD tilt . US "35 t I t > 96 « oooo a . I > t t I ±50 M 200' 10 FEBRUnRT 5-9. 1973 r -« — ►— t — K 24 ■ 2N 10 RPRIL 2^-28. 1973 11000 II I I ^^ 2y HOOO lilt U5 «000 -I I I — t- 75 w» 96 t UDOO (1 — ►— 1 — i — H 80- %'■■ 2S0- 10 JUNE 11-14. 1973 2y <1SOO 75 ueoo . 1 I I — t- 95 FIG. 61 continued. 362 DISCUSSION Because of its geographical position, Lake Ontario was the first of the Great Lakes to receive substantial impact from the activities of western Tiian. It has received, and continues to receive, loadings of -materials originally introduced to other parts of the Systran. This is, of course, particularly true of conservative ions although there is undoubtedly a considerable pass-through of more physiologically active materials. As a result we have only a very sketchy knowledge of what the original quasi-equilibrium state of the system might have been. In the case of the primary producer communities, particularly the phytoplankton, there has been no attempt to determine the previous composition and character- istics of the flora as there has been in Lake Erie (Hohn 1969) and Lake Michigan (Stoermer and Yang 1969). In the case of Lake Ontario, recovery of samples taken before significant environmental perturbation had already occurred may not be possible, since the available evidence suggests that large-scale and so far unreversed changes took place very early in this system. As is generally the case in the Great Lakes, the most extensive and dramatic evidence of such change comes from the fisheries records (Baldwin and Saalfnld 1962; Smith 1972; Parsons 1973). These indicate certain of the original top predator fish populations in Lake Ontario collapsed several decades before similar occurrences in the upper lakes. It would appear, in fact, that the high populations of Atlantic salmon which were unique to Lake Ontario had essentially been exterminated by the turn of the century. Although destruction of the indigenous popula- tions of desirable fish in the lake undoubtedly resulted from a combina- tion of causes, some of which are only indirectly related to changes in primary producer communities, the fact that subsequent attempts to establish artificially managed populations of the same species have met with universal failure indicates that fundamental changes occurred in the Lake Ontario ecosystem as early as the beginning of the present century. Since, as Davis (1966) has noted, early studies of primary producer communities, including phytoplankton, from Lake Ontario are scarce, even compared to the other Great Lakes, the true nature and magnitude of change in the open water phytoplankton community can only be inferred at the present time from comparison of slightly better known sequences in the upper lakes. The majority of historic studies which are avail- able (Burkholder and Tressler 1932; Tressler and Austin. 1940; Tucker 1948; Tressler et al. 1953) dealt primarily or exclusively with bays or other areas which cannot be considered representative of conditions in the open lake. Both these studies, and more recent studies which treat with similar areas or the nearshore waters of Lake Ontario (McCombie 1967; Michalski 1968), however, have reported floras which could only be interpreted as representative of eutrophic waters. In light of reports of gross visual pollution of the nearshore waters of Lake Ontario (MacKay 1930) it would appear that such regions were substantially 363 disturbed before these studies took place, Although direct evidence of floristic change is lacking, it is clear that the chemistry of the lake has been grossly altered since settlement (Beeton 1965, 1966, 1969) and that the standing crop of phytoplankton has been substantially increased (Schenk and Thompson 1965; Matheson and Anderson 1966; Davis 1966, 1969). Comparison of the trends in Lake Ontario with similar trends in the upper lakes leads to the conclusion that Lake Ontario must be the most highly modified of the Laurentian Great Lakes with the possible exception of Lake Erie. Beeton' s data suggest that the degree of chemical change in Lake Erie and Lake Ontario are quanti- tatively similar, although the morphometric oligotrophy (Rawson 1961) of the latter body of water serves to somewhat modify biological effects. Most recent studies have served to emphasize the fact that Lake Ontario is more severely eutrophied than commonly supposed. High levels of phytoplankton standing crop are present in all areas of the lake during most of the year (Chau et al. 1970; Nicholson 1970; Glooschenko et al. 1973) and primary production (Glooschenko et al. 1974) is, among the Great Lakes, second only to Lake Erie and exceeds it during certain seasons. Studies of the composition and seasonal succession of the phyto- plankton community (Nalewajko 1966, 1967; Ogawa 1969; Reinwand 1969; Munawar and Nauwerck 1971) have revealed a flora dominated by species either tolerant of or requiring eutrophic conditions for growth and extreme successional patterns not characteristic of less modified regions of the Laurentian Great Lakes. Species belonging to the oligotrophic diatom association (Hutchinson 1967) which are a major component of the offshore flora in the upper lakes, are apparently largely absent from Lake Ontario. Studies of the nutrient chemistry of the open waters of Lake Ontario in- dicate the presence of high levels of phosphorus and summer depletion of both silica and nitrate. It has been shown that phosphorus is the primary element controlling eutrophication in the Laurentian Great Lakes, and Schelske and Stoermer (1971, 1972) have postulated that increased loadings of this nutrient into the system, in addition to simply increas- ing gross productivity, substantially modify the composition and seasonal succession of phytoplankton flora indirectly. It appears that increased productivity due to increased phosphorus input leads first to depletion of silica and replacement of the perennial diatom flora during the summer stagnation by groups not requiring silica. Further increases in phosphorus loadings result in depletion of nitrogen sources in the epiliranion during stratification and confer competitive advantage on the nitrogen fixing species of blue-green algae. Both the chemical and biological results available to date suggest that Lake Ontario has already passed the first of these geochemical thresholds and is approaching the second. Indeed, as will be discussed later, it appears that nitrogen limitation is reflected in the composition of the late summer flora in certain areas of the lake at the present time. The results of the present study largely confirm the trends and conditions which might be deduced from previous work. It is quite clear that, although Jb^ Lake Ontario is part of the same physical system, it is f loristically in a different province from the upper lakes, above Lake St. Clair. The phytoplankton assemblages present are completely dominated by species which are apparently not indigenous to the upper lakes and which, even under present conditions, are abundant only in nearshore regions which have suffered considerable impact from man's activities, All of the diatom species which Hohn (1969) found becoming predominant in western Lake Erie as pollution increased are present in the offshore flora of Lake Ontario and many of them are the dominant elements of spring and winter assemblages. Species of green algae which are absent or present only in very low abundance in the offshore phytoplankton of the upper lakes completely dominate the summer and early fall flora. Many of these species are capable of producing nuisance conditions of various sorts. Many of the small, colonial species of Stephanodisaus , such as S. bindevanus and 5. tenuis, have been implicated in taste and odor and filter clogging problems in local regions of Lake Michigan (Vaughn 1961) , Some of the species of blue-green algae present such as Aphanizomenon flos-aquae and Anaaystis ayanea are almost universally associated with nuisance summer blooms in temperate lakes. Indeed, considering the abundance and wide distribution of potentially nuisance producing phytoplankton species in Lake Ontario, it is somewhat sur- prising that the most commonly reported nuisance appears to be caused by overgrowths of benthic algae, particularly Cl-adophora spp. One of the more surprising results of our study was the evident almost total absence of certain species which are unive:rsally among the dominant forms in the offshore waters of the upper lakes. We noted less than 50 occurrences of all of the species of the diatom genus Cyclotelta which form the predominant association in the offshore waters of Lake Huron and Superior and are an important component of offshore assemblages in Lake Michigan. Other species usually considered "characteristic" of Great Lakes phytoplankton assemblages, such as ETtizosoZeri'La eviensis , were very rarely noted in our samples. So far as the diatom component of the phytoplankton was concerned, there was a very striking similarity between the trends in abundance of taxa found in our samples from Lake Ontario, particularly the eastern part of the lake, and those reported by Hohn (1969) from western Lake Erie. The elenients of the phytoplankton flora which are common to both Lake Ontario and the upper lakes are those apparently eurytopic species such as Asterionella fovmosa, Fragilaria arotonensiSy Ankistrodss-nus fatoatus, Botryoaoacus bvaunii, Cryptomonas evosa etc. which enjoy almost universal distribution in both oligotrophic and eutrophic lakes. According to Hohn, the absolute abundance of some of the diatom species in this group did not change appreciably in Lake Erie between 1938 and 1965, which furnishes some notion of their tolerance. At the present time the species cited above, and several others, appear to be universally distributed in all areas of the Laurentian Great Lakes. Another striking feature of the species composition of phytoplankton assemblages is the large number of species present whose general distrib- ution includes freshwater habitats with considerable conservative ion 365 contamination and, in many instances, brackish water., In searching the general literature on phytoplankton species distribution one finds, with rather monotonous regularity, dominant and subdominant taxa in Lake Ontario described as having most abundant occurrences in brackish and saline inland waters, This serves to emphasize the fact that, while compositional changes which have occurred in the Great Lakes are generally attributed to eutrophication, in the strict sense, they really result from complex and interacting changes in the total chemical and physical milieu. While chlorides have apparently increased in Lake Ontario by over a factor of 3, it still can hardly be considered as brackish water. It may be, however, that the only species adapted to the physical conditions in the Great Lakes come primarily from saline water, and any considerable increase in conservative ion levels selectively favors increase in their abundance. It would appear that some general factor is operational, as the same distributional tendency is also found in some groups of invertebrates. Another unusual characteristic of phytoplankton assemblages in Lake Ontario, compared to the upper lakes, is the extreme abundance of microflagellates, and particularly apparently heterotrophic species. The same observation has been emphasized by Munawar and Nauwerck (1971). While autotrophic flagellates are universally present and occasionally constitute an important part of the phytoplankton assemblages of the upper lakes, the extreme abundance of such species and particularly the relative importance is, in our experience, highly unusual. Although our work furnishes no direct support for such a hypothesis, it might be inferred that the waters of Lake Ontario have higher organic loadings than the upper Great Lakes. The same might be inferred from the apparently very high levels of "microzooplankton" observed in many of our samples. Although we made no quantitative estimates of abundance of these organisms, many of our samples contained astonishing numbers of ciliate protozoa and small rotifers. The high abundance of such forms was one of the strikingly gross qualitative differences between prepared samples from Lake Ontario and similar preparations made from samples from the upper lakes . Our results also indicate that the seasonal succession of phytoplankton in Lake Ontario is much more pronounced than is characteristic for less disturbed areas of the Great Lakes. The thermal bar (Nalewajko 1966) appears to be an important factor in controlling the early spring changes in abundance and composition of the phytoplankton assemblage. Similar effects have been noted in the upper lakes, but appear to be largely confined to the nearshore waters, whereas the spring pulse following development of the thermal bar appears to proceed all the way across Lake Ontario, According to the available evidence (Gachter et al. 1974) it appears that this strong spring pulse results in selective depletion of nutrients essential to the species dominant in the spring flora, and sets the stage for the development of the thermal tolerant species characteristic of the summer and fall floras. In this regard it must be very strongly emphasized that our results probably represent an atypical case, so far as seasonal succession is concerned. As previously noted. 366 the spring of 1972 was unusually cold and wet. Chandler's early work on the western basin of Lake Erie (1940, 1942, 1944) has demonstrated the profound effects of local meteorological conditions on the abundance and seasonal succession of phytoplankton communities in disturbed areas of the Great Lakes, It is readily apparent that the successional trends noted during the spring of 1973 are more similar to those reported in previous investigations than those noted in the same period of 1972. It should also be noted that any results from monthly or bi-monthly sampl- ing periods should be treated with caution in such a highly forced system. Due to the apparent high reproductive potential of many of the dominant forms in the Lake Ontario phytoplankton assemblage, significant peaks in abundance may have been either missed or considerably under- emphasized. In the present case it is obvious that samples from September 1972 and May 1973 would have been very valuable in attempting to determine the true pattern of seasonal succession. Mthough the extreme degree of instability apparent in the Lake Ontario system renders general conclusions somewhat difficult, certain patterns are apparent. There appears to be a general pattern of development of the spring bloom and subsequent successional changes to develop first at the eastern and western ends of the lake, then spread along the southern shore before becoming evident along the northern shore, and eventually the mid-lake region. Certain species appear to follow slightly different patterns which may be genuine or, in some instances, the result of the particular time frame examined by the sampling sequence, but the overall pattern appears to be reasonably consistent. In this regard Lake Ontario appears to differ significantly from its nearest analog. Lake Erie, where the quantitative and qualitative aspects of the phytoplankton flora appear to be strongly controlled by morpho- metric and nutrient gradients from the western to the eastern end of the lake, Successional patterns in Lake Ontario compare poorly with those noted in the upper lakes, where the only common feature appears to be the nearshore development of a spring bloom which is apparently controlled by the thermal bar. Recent results indicate that a strong shift towards summer dominance by green and blue-green algae, somewhat similar to that noted in Lake Ontario although quantities and dominant species involved are not comparable, is now a feature of the southern basin of Lake Michigan although this has not been noted in previous studies. Our results also indicate that certain regions of the lake are more highly eutrophied than others. In general, the shallow region from the vicinity of Nine Mile Point around the eastern and northeastern shore to Point Petre was the region in which bloom conditions were first noted and where average phytoplankton densities were largest throughout a significant portion of the year. It was also in this region that the highest and most persistent populations of extrenely pollution tolerant forms such as Aphanizomenon flos-aquae and Cosoonodisaus subsatsa were noted. It would appear that at least some of these populations may first develop in the numerous shallow bays in this region and subsequently spread into the open waters of Lake Ontario, Although our samples furnish no direct support for this supposition, similar occurrences were 367 noted at stations in the vicinity of Presqu'ile Bay where there are exten- sive shallows connected to the Bay of Quinte by the Murray Canal, This sort of "morphometric control" of phytoplankton composition, which Gachter et al. (1974) propose as an important mechansim in eutrophied regions of the Great Lakes, is probably also operational in our results from other regions of the lake. It might be suspected that strong gradients would be present in regions of high population concentration and consequent material loadings to the lake, such as areas near Toronto, Hamilton, the Niagara outlet, Rochester, and Oswego. Effects of these regions on phytoplankton abundance and assemblage composition are indeed apparent in our results in a large number of cases but the patterns are less consistent than those visible in the eastern region of the lake. In this respect it should be pointed out that while we have rather loosely referred to stations nearest shore as nearshore samples, none of our stations were actually in the highly impacted nearshore zone as common- ly defined in recent work on the Great Lakes. 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