541 Distribution and Occurrence of Gymnodinium breve on the West Coast of Florida, 1964-65 By Alexander Dragovich and John A. Kelly, Jr. SPECIAL SCIENTIFIC REPORT-FISHERIES Na 541 UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE B U RE AlToF^COMMERaAr^lSHERiir UNITED STATES DEPARTMENT OF THE INTERIOR Stewart L. Udall, Secretary Joliii A. Carver, Jr., Under Secretary Stanley A. Cain, Assistant Secretary for Fish and Wildlife and Parks FISH AND WILDLIFE SERVICE, Clarence F. Paut/,kp, Commissioner Bureau of Commercial Fisheries, Donald L. McKernan, Director Distribution and Occurrence of Gymnodinium breve on the West Coast of Florida, 1964-65 By ALEXANDER DRAGOVICH and JOHN A. KELLY, JR. United States Fish and Wildlife Service Special Scientific Report--Fisheries No. 541 Washington, D.C. December 1966 CONTENTS Page Introduction 1 Sampling methods and laboratory techniques 1 Distribution of Gymnodinium breve 3 Geographic distribution 3 Monthly occurrence 3 Vertical distribution 3 Environmental factors 8 Temperature 8 Precipitation 8 Salinity 8 Relation of temperature to occurrence of Gymnodinium breve 13 Relation of salinity to occurrence of Gymnodinium breve 14 The role of land nutrients and precipitation in the distribution of Gymnodinium breve 14 Comparison of distribution of Gymnodinium breve in 1964-65 with that previously reported 14 Literature cited 15 Distribution and Occurrence of Gymnodinium breve on the West Coast of Florida, 1964-65^ By ALEXANDER DRAGOVICH and JOHN A. KELLY, JR., Fishery Biologists Bureau of Commercial Fisheries Biological Laboratory St. Petersburg Beach, Fla. 33706 ABSTRACT The distribution and monthly occurrence of Gymnodinium breve, the Florida red-tide organism, were determined over a period of 13 months (in 1964-65) in the coastal waters of west Florida. Counts of G. breve varied from 0 to 53,800 cells per liter of water; no fish kills were observed. The organism was present at all stations from 9.3 km. (5 miles) to 37.1 km. (20 miles) offshore. It was not present in samples from Tampa Bay, and it was found only twice in samples from Charlotte Harbor. The highest occurrence of G. breve was in samples taken 27.8 km. (15 miles) offshore. Vertical distribution of the species was greatest at the surface and at 5 m. and lowest at 20 m. The largest concentrations of G. breve occurred in September during a period of reduced salinity and temperature. Because these two factors are innportant to the ecology of the organism, their relation to the presence or absence of G. breve is discussed. G. breve were found within the tennperature range 13.8° to 30.6° C. It was absent or rare at both the low and high temperatures; cell densities greater than 1,000 per liter were observed from 26.0° to 27.9° C. The organism occurred at salinities ranging from 33.68 to 37.07 p.p.t. The highest concentration of cells and incidence was noted within the salinity range 35.00 to 36.90 p.p.t. INTRODUCTION Gymnodinium breve Davis is the nonthecate dinoflagellate that causes red tide inestuarine and neritic waters along the west coast of Florida. Dense concentrations of the organism discolor the water and produce toxic metabo- lites that cause catastrophic mortality among fishes and other marine animals. References to previous reports on the distribution and seasonal occurrence of G. breve were pre- sented by Finucane (1964). Rounsefell and Nelson (1966) reviewed published and un- published papers and data on red tide, and Rounsefell and Dragovich (1966) examined the relation between oceanographic factors and abundance of the Florida red-tide or- ganism. At the Red- Tide Symposium held in October 1964 at St. Petersburg Beach, Fla., past and current red-tide research was ex- amined and several suggestions for future studies were presented (Sykes, 1965). 1 Contribution No. 30, Bureau of Commercial Fisheries Biological Laboratory, St. Petersburg Beach, Fla. This study presents information on the seasonal occurrence and distribution of G. breve in an area of recurrent red-tide out- breaks covering about 2,800 sq. km. (1,600 square miles) along the west coast of Florida. Systematic monthly collections of such mag- nitude to monitor G. breve and observe oceanographic conditions have not been made previously in the region. Our work made it possible to corroborate and extend information on several aspects of the ecology of G. breve in Florida waters. SAMPLING METHODS AND LABORATORY TECHNIQUES From February 1 964 through February 1 965, water samples were collected monthly to de- termine the abundance of G. breve and to measure water temperature and salinity. We established 22 stations in Tampa Bay, Char- lotte Harbor, and at regular intervals along a series of transects extending 37.1 km. (20 miles) offshore (fig. 1). The water column was sampled during daylight at 5-m. intervals from surface to bottom. Collecting procedures, techniques of enumerating G. breve, and tem- perature and salinity determinations were identical to those described by Dragovich, Finucane, and May (1961). The data on pre- cipitation were obtained from the U.S. Environmental Science Service Administra- tion. WEST GULF COAST HILLSBOROUGH BAY JOHNS PASS a a a a a S A.M P L I N G S T A OF ANNA MARIA KEY a a a a MEXIC O 27 — VENICE INLET a a a a BOCA GRANDE P a a a a 8 3' Figure 1. — Sampling stations along the west coast of Florida. The term "bloom" used in this paper follows the definition by Finucane (1964): "Any con- centration of G. breve exceeding the normal population level of approximately 1,000 cells per liter." During previous red-tide studies, lethal blooms of G. breve usually consisted of 250,000 organisms per liter or more (Finucane and Dragovich, 1959). DISTRIBUTION OF GYMNODINIUM BREVE The distribution of phytoplankton may be portrayed as 4-dimensional, consisting of latitudinal, longitudinal, vertical, and temporal components. In this paper, distribution is examined primarily in the light of previous studies of the Florida red tide (Dragovich, 1961; Finucane, 1964). Geographic Distribution G. breve was found in 24 percent of all samples, and was present in one or more collections at all offshore stations in concen- trations of <10 to 53,800 cells per liter (figs. 2a, 2b, 2c, and 2d). The scale shown in the legend of the figure represents only one-half of the profiles; September values are shown with interrupted lines because they exceed scale. The top value (September) represents the number of cells at the surface; the lower, cells at 5 m. The percentage of samples in which G. breve occurred (hereafter identified as incidence) was highest (32.3 percent) at stations off Venice Inlet, lowest at stations off Boca Grande Pass (23.0 percent), and intermediate off Anna Maria Key (29.7 percent) and Johns Pass (29.0 percent). In terms of distance from shore, incidence of G. breve was highest at the 27.8-km. (15-mile) stations and least at the 9.3-km. (5-mile) stations (fig. 3). G. breve was absent from all Tampa Bay samples and was recorded at Charlotte Harbor only in April and July, in concentrations of less than 100 cells per liter. Monthly Occurrence Counts of G. breve were less than 1,000 per liter in each month except February and Sep- tember. After the high incidence in February 1964, numbers declined in March and April and remained relatively low through August. Both numbers and incidence increased at all offshore stations in September, and cell counts were higher than in any previous month. Numbers decreased in October and November, when monthly incidence was the lowest during the study. Both numbers and incidence in- creased again in December. The incidence in that month was highest 27.8 km. (15 miles) and 37.1 km. (20 miles) offshore from Johns Pass, Anna Maria Key, and Venice Inlet; samples off Boca Grande yielded no G. breve. Adverse weather in January and February 1965 prevented collections at some stations, but in the areas sampled (Tampa Bay, Johns Pass, and Venice Inlet), the incidence of G. breve was low. Vertical Distribution G. breve was collected at least once during the study at each offshore station and each sampling level. The highest incidence of the organism was at the surface (33.3 percent) and at 5 m. (30.5 percent), lowest at 20 m. (20.7 percent), and intermediate at the 10- and 15-m. levels. Samples containing 1,000 cells or more per liter were recorded only at the surface and at 5 m. (figs. 2a and 2c); 67 percent of these high counts were at the surface. Finucane (1964) also observed higher incidence of G. breve at the surface than at the bottom. 1 - 21 - II nut T ti iiici 1 II IIUS 1 •11(1 k i mil pisi . \ / 1 ii» iiiii ;i T T "T "' ^ V C unci •- A -— 1 ^ '"" ■ II - m - ■"'■ \ ^^ - 1 -, 11 - T •f "J"' C 1. \\ j 1. IICl ir 1 1 / % IMf :i - FIllllll 1114 VcillI PCI lll[> Figure 2(a). —Vertical and temporal distribution of G. breve at sampling areas along the west coast of Florida. t mil Fits I. lilt iiiii lET ■l ltd i'liiiiE nil ciiii nt mil Figure 2(b). — Vertical and temporal distribution of G. breve at sampling areas along the west coast of Florida. 1 ^ II mis II HIES II mil s mil M 5 c 1 1 iiiii riti ) / \ III! •till \ t IfllCl 1 ^ "'" \ \ J 1 no \ Y^iiiiK riss / i IMI \ tdil ril tint 11 - 1 - ■ — " ' ---| 1 ---T--- ^ --'l'-^ >• I -^ 11 > ^ -. r - ! J IIIISI 1114 Figure 2(c). — Vertical and temporal distribution of G. breve at sampling areas along the west coast of Florida. 1 . II ■ " it - ~ ' 1 21. 1- 21- 21 •IkIS II IIKS II lilts 1 lilts c 1 Liiiis riti / I III! •llll ^^ Itl C unci ^/ mil \ \ i 1 IICI \ y?finiii iiss \ eiiit Ki uiii ..^^^ -- """1 ^ 1 " ■ IIIIIII UK ■ ■ ■ i — ' — ' w vJ/ — ^^{ lllltIT llll \ V _ .__ ; 1 ' %P --^^-. ^/ _i-^{ rtiiiiiT 1 V Figure 2(d). — Vertical and temporal distribution of G. breve at sampling areas along the west coast of Florida. Fibrujry 1964 April Incidence of Gymnodlnium breve layi SMIIts lOMIKs ISMIIts ?OMII>$ Toll! OC€©€ © CDe€)€€) e oo®€© e oo®o© ® 0©0©© (!) 0€0€€ € OCD©©® © 0©0©© © 0©©€© © O © O O O © 0©©00 © Mi> July Autust Septem bet October Dtcember Febr ua ry Figure 3. — Incidence of G. breve (percentage of total samples containing the organism) by month and distance from shore along the west coast of Florida, February 1964 to February 1965. Data are combined for Tampa Bay and Charlotte Harbor, and for the four series of stations shown in figure 1. Solid black circle is equal to 100 percent. ENVIRONMENTAL FACTORS The distribution and abundance of marine phytoplankton are influenced by temperature and salinity. The geographic distribution of phytoplankton is governed by temperature. The latitudinal occurrence of phytoplankton in neritic and estuarine areas is controlled pri- marily by salinity fluctuations which, in turn, are influenced by precipitation. Temperature Maximum water temperature (31.1° C.) was observed in August at Charlotte Harbor, and the minimum (13.8° C.) in February, 27.8 km. (15 miles) off Johns Pass, near the bottom. Low temperatures extended from December through March in most of the area (table 1). Warming began in March, and temperatures were highest in July and August. Temperature decreased in most areas from September through December. Off Johns Pass this decline continued through February 1965 and off Anna Maria through January. Thermal gradients were negative in March and September, 27.8 km. (15 miles) and 37.1 km. (20 miles) offshore. The maximum gradient (3.7° C.) occurred in September, 37.1 km, (20 miles) offshore. For the remaining months, vertical variations of temperature never ex- ceeded 1.6° C, but they were greater than 1° C. 15 times. Precipitation Heavy rainfall is often given as a likely factor in the production of red tide (Numann, 1957). Although it has not always been asso- ciated with outbreaks of Florida red tide, it must be considered as one of the factors favoring red-tide outbreaks. Precipitation during 1964 at St. Petersburg, Bradenton, Punta Gorda, and Fort Myers was well below the long-term means, although it was 16.15 cm. (6.36 inches) above the mean at Tampa (table 2). The lack of red-tide out- breaks during the present study was coinci- dental with the relatively low rainfall. Salinity The maximum salinity (37.10 p.p.t.) was 20 miles off Venice Inlet, near the bottom, in July; the minimum (17.83 p.p.t.) was in Hills- borough Bay, at the surface in April. Seasonal changes of salinity are similar at all offshore stations (fig. 4). Monthly changes in salinity were nnore pronounced at stations 5 and 10 miles offshore than at 15 and 20 miles. Salinity increased steadily at most stations from February through July and began to decline in August during the rainy season. It in- creased in November but remained below the maximum summer value from November through February. In terms of distance from shore, salinity increased progressively from 5 to 20 miles offshore at all transects only in April and December (fig. 4), Existence of water masses with reduced salinity at stations 20 miles offshore was particularly obvious in Septem- ber. Salinity increased with increasing depth at offshore stations throughout most of the in- vestigation.. The gradient exceeded 1 p.p.t. during February, June, August, September, October, and November. Table 1. — Mean monthly temperatures of water samples fall depths combined) at stations along the west coast cf Florida, 1964-65 (station locations are shown in figure 1; Sampling area --ind month Distance offshore 9.3 km. (5 miles ) 18.5 km. (10 miles) 27.8 km. (15 miles) 37.1 km. (20 miles) Johns Pass 1964: February. . March April May June July August . . . . September. October. . . November. . December. . 1965: January. . . February. . Anna Maria Key 1964: February March April May June July August September October November December 1965: January February Venice Inlet 1964: February March April May June July August September October November December 14.6 15.6 21.9 24.8 28.2 29.3 29.5 27.7 23.9 23.1 20.3 19.2 18.5 15.7 20.5 23.5 25.7 28.9 29.7 29.8 27.7 23.6 24.0 18.4 16.2 19.1 15.2 20.4 23.3 26.0 28.3 29.7 29.8 27.0 22.1 23.2 21.0 14.4 15.5 21.4 24.8 28.1 29.4 29.3 28.2 24.1 23.2 20.8 19.2 13.3 15.7 19.7 22.9 25.8 28.6 29.6 29.6 27.7 23.8 24.0 18.3 17.2 18.9 15.4 19.6 23.0 25.9 28.3 29.7 29.8 26.8 22.4 22.9 21.0 14.9 15.4 21.0 24.7 28.0 29.5 29.2 27.8 24.2 22.9 21.4 19.2 18.3 15.2 19.0 22.8 25.3 28.2 29.5 29.8 27.6 24.0 24.0 19.0 17.6 18.8 15.3 18.9 22.6 25.6 28.1 29.7 29.8 26.6 22.7 22.8 21.1 14.9 17.6 20.3 24.4 27.6 29.5 29.4 27.1 24.6 22.6 21.8 19.4 18.3 15.4 18. 22. 25. 27. 29. 29.6 27.4 23.6 23.5 19.4 17.9 18.7 16.4 19.2 22.3 25.3 27.8 29.8 29.8 26.4 23.0 22.6 21.8 Table 1 . — Continued Sampling area and month Distance offshore 9.3 Ian. (5 miles] 18.5 km. (10 miles) 27.8 km. (15 miles ) 37.1 km. (20 miles) Boca Grande Pass 196<;: February. . March April May June July August. . . . September. October. . . November. . December. . 15.3 21.2 2'i.O 27.0 28.9 29.7 30.1 27.2 22.2 21.9 20.6 15.0 21.1 23.7 26.4 28.7 30.1 30.1 27.-4 22.6 23.1 21.6 14. 20. 23. 26. 28. 30. 30.0 27.4 23.5 21.6 15.0 20.0 22.7 25.6 28.2 30.1 29.9 27.3 22.3 21.7 Sampling area and month Locations Upper 2 stations, (Old Tampa Bay and Hillsborough Bay) Lower 2 stations (Tampa Bay) Tampa Bay 1964: February March April May June July August September October November December 1965: January 14.4 20.4 21.2 24.6 30.0 29.9 29.5 28.6 24.2 22.4 18.8 18.8 14.4 20.8 21.8 24.9 29.8 29.8 28.0 28.8 24.5 22.2 18.9 19.0 Locations Upper station Lower station Charlotte Harbor 1964: February March ^rll May .- June July August September October November December 15.4 21.5 25.1 27.4 29.7 30.5 30.9 28.0 21.9 22.4 22.0 10 o w •H (U cd -p rH J5 a) In tJ O O cH ^ +» cu CO jq S o __ _ _ 1 • r_{ rH r^ I>- sf ^D to in o n ON rH o 0) O^ ^ O ir\ tc a^ O O sD 1 ^ ON CNJ vO Eb m ro n CNJ cv OJ OJ r~\ n C\) r\j CNJ m u~\ H § m CvJ .0 ^a m CO rn nD nD sf CM CO r- ON -st in sf O o 1 O c\j in ND ■-o rH O OJ H CvJ r-{ OJ n 1- r-i i-i rH rH rH a £> r\ i> r\j c^ O Sf ON c^ o in rH -sT in >} in c\ [> r-\ OJ OJ m ■^ in m in m in sf fr\ n m m in en — ■ — ^-' ■^ ■— ' ^ ^ _ __^ • CNJ o o ON ON r^ CO CO in nD CO nD on -sf o r^ rH H CO O ON o O OJ in O OJ rH Q T\ rH CNJ n rH OJ rH rH OJ r~i rH r-i rH H ^_^ _, ^ ^^ __^ ,_, > 0 H [> v£) CO nD l> ON 00 sf 00 [> OJ o ON Ov CO \o n Nf ^0 I> o in r^ OJ OJ CM o :z. d rH rH '^ rH rH _^ ^ ^_^ ^ ^ ,_^ • to in m \0 00 in OJ ON NO O CO CO ON CO o yD ^ CO CO t> 00 m in CO o o rn O ON o vC in o sf p. eg o LH n~> CO to [> OJ .- !>• in in ^ m OJ to OJOO in nd -st CO E> si in tc ON CO vD ■ — ■ — - — — ^ _^^ ^ ^ _^ ,_^ • ON rH VD r^ -J- [> £> O rH to y£> nD CO rH i" CNJ vD ON t> C\J CO t> ^ I> to ON CNJ m cn 4 O^ in CO d 00 -4" ON ^ sj m nD ^ c^ OJ ^ ^-^ rH ^-' '—' "-^ \0 a^ >, to vO CNJ »n OJ no n o- CO ON O CO to O r-\ (^ to CM O vC r-\ O cy £> P-l 00 OJ o o cr- [> ON ON 00 £> O^ in CO [> t> OJ 0^ in ^-^ "-' '—^ -^ ^ ^_^ ^_^ „_^ ,_^ 0) r-H VD CNJ Nt CO sf ^D nD O t^ I> CO nD in g r~\ CO n nD Oj ^ !>■ £> o f^ CO in ON m •-3 Cvj rn O \D C^ [> ^ ^D OJ <^ 0C3 sf CO in ^ ^ ^ __^ __^ ■sf O CO CO m in rH ON o rH O o m rH ^ ITI o~i in in 00 ON \D MD sj m in m 00 in C\ OJ OJ r^ Oi OJ OJ <- r- rH cn O en H ,_^ __^ __^ ^^^ ,_^ r\j O H r-i sf r^ O 00 C\ 00 o O Nf n ^ CO C\i in to ^D CO 00 v£) OJ ON CO vO m c- O (^ ni nj OJ ' CM rH ^— ' ■^ ■"— ' "-' ■^ ^ _ _ _ ^ u ^ o o Oi in m tc ^ O t> sf CM OJ m C\ O vD ON i> c-- tn 1> i-i in CO rH nD n£) S ir> St r^ r^ n-i r^ r^ s r~i d OJ CM CM OJ _ _^ _^ ^ ,^^ c\ O <-{ I> sf in CO G O. OJ en O H m c\ ON O (^ 00 OJ I> CC C ^ sf rn OJ 00 ti. E> m r'l in OJ in CM IP s sf CM m OJ CM ^_^ ,_^ , ^ ,_^ ,_^ I> O O CO r^ ^ CO I> tc O vO 00 CVI sf •-3 tc ^ "^ O rH I> sf cc v£ v£) O- CO m n£) IT fn OJ in OJ r^ CNj rn t^ rH rH CM H OJ "■ — ■ ^^ "'^ ' /) H V V J ^ bfl 1) u zl J3 CO tJ J- w T3 V a fn C tH w s c 0) o +- s OJ (0 P G c a :^ > CL CO 0) c c CO •H a 0- Tj CC •r -P +J a E CO i- C C p. c > t J- cc cr a > ^ t ^ 1 11 MILES OFFSHORE! 5 10 15 20 JOHNS PASS 1964-65 Figure 4. — Monthly mean salinity and precipitation at stations along the west coast of Florida, February 1964 to February 1965. Mean salinities (samples taken at 5-m. intervals in the water column) are shown by vertical .bars; superimposed graphs denote precipitation. Salinities were higher at stations in Char- lotte Harbor (from 15.35 to 35.52 p.p.t.). Salinity in Tampa Bay may vary with the stage of the tide by as much as several parts per thousand during a 24-hour period (un- published data, Bureau of Conrimercial Fisheries Biological Laboratory, St. Peters- burg Beach, Fla.). Since the Bay stations were sampled without regard to tidal stage, the salinities deternnined may not represent temporal changes for the a rea. 12 RELATION OF TEMPERATURE TO OCCURRENCE OF GYMNODINIUM BREVE Several studies have been made on the effect of temperatures on G. breve under field conditions and in the laboratory. Aldrich(1959), who studied the effect of temperature upon bacteria-free cultures of G. breve, reported some survival below 7° C. and a slowing down at 15° C. Seven years of field data analyzed by Rounsefell and Nelson (1964) indicated that G. breve thrives frona 16° to 27° C, but that outside this range the organism occurs only in small numbers. The adverse effect of low tennperature upon blooms of G. breve was observed in 1957 (Finucane, 1958). Concen- trations were reduced to a few cells per liter after the water temperature dropped to 9.9'-' C. In our study, G. breve was observed at temperatures from 13.8° to 30.6° C. The highest numbers of samples containing the organism were recorded within the ranges from 14.0° to 15.9° C. and from 26.0° to 27.9° C. (table 3). Incidence was low at the maximum and minimum temperatures. Cell densities greater than 1,000 per liter were recorded at 26.0° to 27.9° C. The relation between the occurrence of G. breve and temperature is difficult to deter- mine from our data because of the low inci- dence and concentrations encountered. On the basis of laboratory studies by Aldrich (1959) and field observations by Finucane (1964) and Rounsefell and Nelson (1964), the temperatures observed were generally favor- able for the proliferation of G. breve. The Table 3. — Temperature and salinity ranges within which G. breve occurred in the coastal waters of west Florida (February 1964 through February 1965) Temperature Range (°C. ) Samples Positive samples Percentage of positive samples Percentage of positive samples within this range 12.0-13.9 14.0-15.9 16.0-17.9 18.0-19.9 20.0-21.9 22.0-23.9 24.0-25.9 26.0-27.9 28.0-29.9 30.0-31.9 Number 3 73 24 95 108 147 90 95 168 43 Number 1 40 9 23 27 17 17 40 22 6 Percent 33.3 54.8 37.5 24.2 25.0 11.6 18.9 42.1 13.1 14.0 Percent 0.5 19.8 4.4 11.4 13.4 8.4 8.4 19.8 10.9 3.0 Total 846 202 274.5 100.0 Salinity Range (p . p . t . ) Samples Positive samples Percentage of positive samples Percentage of positive samples within this range 0.0-20.9 21.0-22.9 23.0-24.9 25.0-26.9 27.0-28.9 29.0-30.9 31.0-32.9 33.0-34.9 35.0-36.9 37.0-38.9 Number 25 19 22 14 8 13 12 166 554 10 Number 0 0 0 0 0 0 0 44 156 1 Percent 0 0 0 0 0 0 0 26.5 28.2 10.0 Percent 0 0 0 0 0 0 0 21.9 77.6 0.5 Total 843 201 64.7 100.0 13 absence of extensive blooms of G. breve reported here is probably attributable to fac- tors other than unfavorable temperature. RELATION OF SALINITY TO OCCURRENCE OF GYMNODINIUM BREVE Laboratory and field studies have been made also on the effect of salinity on G. breve. In bacteria-free cultures, Aldrich and Wilson (i960) observed good growth within the salinity range 27 p.p.t. through 37 p.p.t., and poor growth at values lower than 24 p.p.t. or higher than 44 p.p.t. In media with a salinity of 13.7 p.p.t. or less, no live cells of G. breve were detected 1 day after innoculation. Field data on occurrence of G. breve at various salinities vary (table 3), and agree only par- tially with the laboratory observations by Aldrich and Wilson (I960). The most favorable salinity range for growth of G. breve under natural conditions probably is between 21 and 37 p.p.t. (Finucane, 1964). According to Rounsefell and Nelson ( 1 964), the upper salinity limit for good growth appears to vary with temperature, and salinity becomes linniting at 37 p.p.t. when temperature exceeds 23° C. In our study G. breve occurred at salinities from 33.68 to 37.01 p.p.t. The majority of samples containing the organism were from water of salinity of 35.0 and 36.9 p.p.t. (table 3). Highest counts were during periods of reduced salinity (February and September- - see figs. 2a and 2c). G. breve occurred only once in samples with salinity above 37.00 p.p.t., and in samples with salinity below 33.0 none were found. The salinities at which G. breve occurred in our study fell within the range at which Aldrich and Wilson ( 1 960 ) obtained good growth under laboratory conditions. Furthermore, on the basis of salinities observed by others (table 4), conditions in the area of investigation were favorable for blooms of G. breve even though no outbreak appeared. Thus our obser- vations support the view that favorable salinity alone may not be the major factor in the proliferation of G. breve (Aldrich and Wilson, 1960; Dragovich, 1963; Finucane, 1964). THE ROLE OF LAND NUTRIENTS AND PRECIPITATION IN THE DISTRIBUTION OF GYMNODINIUM BREVE Nutrients from land drainage play an im- portant role in outbursts of phytoplankton (Wilson and Collier, 1955; Lucas, 1955; Wilson, 1951; Numann, 1957). A reduction in salinity in coastal waters is usually the first condition associated with periods of rainfall and in- creased land drainage. Offshore salinity was above 35.00 p.p.t. in 80.1 percent of the obser- vations during the period of study; thus the offshore environment was essentially marine most of the time. Consequently, additions of nutrients via land drainage may have been insufficient to produce conditions required for lethal red-tide blooms. On the basis of the incidence and counts of G. breve, the favorable conditions for its proliferation fell during February, March, and September 1964, the months of heavy rainfall and reduced salinity. Wilson in a simultaneous and independent investigation tested the suitability of waters from the study area for growth of G. breve in unialgal cul- tures (personal communication). ^ He found that the water was most suitable for growth of the organism in February, March, August, September, and October 1964. Table <4. — Salinity ranges within which Gymnodinium breve was reported under field conditions Favorable range Source P.p.t. 21.0-36.9 Finucane (1964) 31.0-34.00 Hela (1956) 32.5-33.2 Ketchum and Keen (1948) 33.49-34.50 1. Chew (1953) 35.2-36.7 Dragovich (1961) 33.0-37.0 Odum, Lackey, Ifynes, and Marshall (1955) 35.5-37.0 Gunter, Williams, Davis, and Smith (1948) 30.5-37.0 Rounsefell and Nelson (1964) COMPARISON OF DISTRIBUTION OF GYMNODINIUM BREVE IN 1964-65 WITH THAT PREVIOUSLY REPORTED The seasonal, spatial, and vertical distri- bution of G. breve was essentially the same as observed during other non-red-tide years off the coast of west Florida (Finucane, 1964; Rounsefell and Nelson, 1964). Usually the organism was absent in bays but present in neritic areas. Our observation that G. breve is a relatively stenohaline organism which, during a non-red-tide year, occurs in low concentrations in the neritic waters of west Florida is in agreement with the findings of Finucane (1964), Aldrich and Wilson (I960), Dragovich (1963), and Rounsefell and Nelson (1964). Wilson, William B., Florida State University, Talla- hassee, Fla. 14 LITERATURE CITED ALDRICH, DAVID V. 1959. Physiological studies of red tide. U.S. Fish Wildl. Serv., Circ. 62: 69-71. ALDRICH, DAVID V., and WILLIAM B. WILSON. 1960. The effect of salinity on growth of Gymnodinium breve Davis. Biol. Bull. (Woods Hole) 119(1): 57-64. CHEW, FRANK. 1953. Results of hydrographic and chemical investigations in the region of the "Red Tide" bloom on the west coast of Florida in November 1952. Bull. Mar. Sci. Gulf Carib. 2(4): 610-625. DRAGOVICH, ALEXANDER. 1961. Relative abundance of plankton off Naples, Florida, and associated hydro- graphic data, 1956-57. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 372, iii + 41 p. 1963. Hydrology and plankton of coastal waters at Naples, Florida. Quart. J. Fla. Acad. Sci. 26(4): 22-47. DRAGOVICH, ALEXANDER, JOHN H. FINUCANE, and BILLIE Z. MAY. 1961. Counts of red tide organisms, Gym- nodinium breve, and associated oceano- graphic data from Florida west coast, 1957-59. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 369, iii + 175 p. FINUCANE, JOHN H. 1958. Occurrence of red tide organisms. In Annual report of the Gulf Fishery Investigations for the year ending June 30, 1958, U.S. Fish Wild. Serv., p. 68- 69. 1964. Distribution and seasonal occurrence of Gymnodinium breve on the west coast of Florida, 1954-57. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 487, iv + 14 p. FINUCANE, JOHN H., and ALEXANDER DRAGOVICH. 1959. Counts of red tide organisms, Gym- nodinium breve, and associated oceano- graphic data from Florida west coast, 1954-57. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 289, iv + 220 p. GUNTER, GORDON, ROBERT H. WILLIAMS, CHARLES C. DAVIS, and F. G. WALTON SMITH. 1948. Catastrophic mass mortality of ma- rine animals and coincident phytoplank- ton bloom on the west coast of Florida, November 1946 to August 1947. Ecol. Monogr. 18(3): 309-324. HELA, ILMO. 1955. Ecological observations on a locally limited red tide bloom. Bull. Mar. Sci. Gulf Carib. 5(4): 269-291. KETCHUM, BOSTWICK H., and JEAN KEEN. 1948. Unusual phosphorus concentrations in the Florida "red tide" sea water. J. Mar. Res. 7(1): 17-21. LUCAS, C. E. 1955. External metabolites in the sea. In Papers in Marine Biology and Oceanog- raphy, p. 139-148. Deep-Sea Res. 3(Suppl.). NUMANN, WILHELM. 1957. Naturliche und kunstliche "red water " mit anschliessenden Fischsterben im Meer. Arch. Fischereiwiss 8(3): 204- 209. ODUM, HOWARD T., J. B. LACKEY, JACQUELINE HYNES, and NELSON MARSHALL. 1955. Some red tide characteristics during 1952-1954. Bull. Mar. Sci. Gulf Carib. 5(4): 247-258. ROUNSEFELL, GEORGE A., and ALEXANDER DRAGOVICH. 1966. Correlation between oceanographic factors and abundance of the Florida red tide (Gymnodinium breve Davis) 1954-61. Bull. Mar.Sci. 16(3);404-412. ROUNSEFELL, GEORGE A., and WALTER R. NELSON. 1964. Status of red-tide research in 1964. Ala. Mar. Res. Lab. Tech. Rep. 64-1, 192 pp. ROUNSEFELL, GEORGE A., and WALTER R. NELSON. 1966. Redtide research summarizedto 1964 including an annotated bibliography. U.S. Fish Wildl. Serv., Spec, Sci. Rep. Fish. No. 535, iv + 85 p. SYKES, JAMES E. 1965. Bureau of Commercial Fisheries symposium on red tide. U.S. Fish Wildl. Service., Spec. Sci. Rep. Fish. 521, iii + 1 1 p. WILSON, D. P. 1951. A biological difference between natural sea waters. J. Mar. Biol. Ass. U.K. 30: 1-20. WILSON, WILLIAMB., and ALBERT COLLIER. 1955. Preliminary notes on the culturing of Gymnodinium brevis Davis. Science 121 (3142): 394-395. MS. #1552 15 GPO 916-271 ERRATA SHEET Distribution and occurrence of Gymnodinium breve on the west coast of Florida, 1964-65, by Alexander Dragovich and John A, Kelly, Jr. U.S. Fish and Wildlife Service, Special Scientific Report-Fisheries No. 541, p. 6. GPO 9 18.632 Created in 1849, the Department of the Interior — a depart- ment of conservation — is concerned with the management, conservation, and development of the Nation's water, fish, wildlife, mineral, forest, and park and recreational re- sources. It also has major responsibilities for Indian and Territorial affairs. As the Nation's principal conservation agency, the De- partment works to assure that nonrenewable resources are developed and used wisely, that park and recreational re- sources are conserved for the future, and that renewable resources make their full contribution to the progress, pros- perity, and security of the United States — now and in the future. UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE BUREAU OF COMMERCIAL FISHERIES WASHINGTON, D.C. 20240 U.S. POSTAGE AND FEES PAID DEPARTMENT OFTHE INTERIOR OFFICIAL BUSINESS Return this sheet to above address, if you do NOT wish to receive this material Q, or if change of address is needed | | (indicate change). .^auBBlSL Librarian Marine Biological Lab., Woods Hole, Mass. 02543 SSR 7