THE ABUNDANCE, DISTRIBUTION, AND BIOLOGY OF PLANKTON IN LAKE MICHIGAN
WITH THE ADDITION OF A RESEARCH SHIPS OF OPPORTUNITY PROJECT

Final Report of
Office of Naval Research Project NR 104-818,
Contract Nonr-1224(53)

David C. Chandler - Project Director

Report by
Andrew Robertson, Principal Investigator

Distribution of this document is unlimited.

Special Report No. 35

Great Lakes Research Division

The University of Michigan

Ann Arbor, Michigan

1968

TABLE OF CONTENTS

ABSTRACT .. o ....... o ............. . v

SUMMARY o . o . o . o . o . o . o ........... . 1

THE APPLICABILITY OF THE CONTINUOUS PLANKTON RECORDER

TO PLANKTON STUDIES IN LAKE MICHIGAN 5

Selection of a Suitable Silk « 7

Determination of Silk Winding Speed o 17

Determination of Towing Depth . o • . . . . 20

A COMPARISON OF SOME BIOLOGICAL PROPERTIES SAMPLED ON
THE CRUISE OF A MERCHANTMAN FROM DETROIT, MICHIGAN, TO

JjXJLJdUa, Dirii.J.lN o.o.o.o.o.o.. ......... <uO

Temperature .. o . o . c . o ............ . 27

Conductivity o . o . o • <> « o . o • • . 29

Particulate Organic Matter and Dissolved Organic

iiauLer o**oco«o*o«oo««*«««*««« -j/l

Composition of the Zooplankton Communities 36

REFERENCES ooo*o*e«o«o««««**«»«*»«« 43

111

THE ABUNDANCE, DISTRIBUTION, AND BIOLOGY OF PLANKTON IN LAKE MICHIGAN
WITH THE ADDITION OF A RESEARCH SHIPS OF OPPORTUNITY PROJECT"''

ABSTRACT

This report summarizes the results obtained from a study on the abun-
dance, distribution, and biology of plankton in Lake Michigan as well as
from a Research Ships of Opportunity cruise.

Modifications needed to adapt the Continuous Plankton Recorder for use
in the Great Lakes are presented in detail. The major change from the pro-
cedure used in the marine Recorder survey on the plankton of the North
Atlantic is the use of a finer silk for filtering.

A detailed presentation is also made of the scientific results obtained
during a cruise aboard a Research Ship of Opportunity from Detroit, Michigan
to Bilboa, Spain* Studies were made on the changes in composition of the
zooplankton community as well as in the amounts of particulate organic
matter and dissolved organic matter encountered during this cruise. The
diversity and quantity of microcrustaceans were found to be greater in the
lakes than in the comparable marine environments. Particulate and dissolved
organic matter followed very similar trends in relative abundance and were
especially high in western Lake Erie and at the mouth of the St. Lawrence
River .

1

We wish to acknowledge the contribution of Mrs. Sharon C. Czaika, who

assisted with all phases of the work and who carried out much of the work

with the diaptomids; and of Mrs. Jeanne Rose, who carried out most of the

analyses of the samples from the Research Ships of Opportunity cruise. Also

we would like to express thanks to the Edinburgh Oceanographic Laboratory of

the Scottish Marine Biological Association and especially the Director,

R. S. Glover, for great assistance both in the work using Continuous Plankton

Recorders in the Great Lakes and in analyzing our marine Recorder tow.

SUMMARY

This is the final report on ONR Project NR 104-818, Contract Nonr-1224
(53), which was conducted from March 1, 1965 to February 29, 1968 with a
continuation to May 31, 1968. Objectives of the study are listed below, with
a brief summary of the results « Some results from this study have been
published, as indicated by the bibliography; therefore emphasis in this
report will be on unpublished datao

Ob^eotive 1

To determine the adjustments needed to adapt the Continuous Plankton
Recorder for use in conducting a survey of the plankton of the Great Lakes.

Results: It has been determined that the Recorder should be adjusted
in the following ways for use in the Great Lakes: (1) It should be loaded
with #7 (82 meshes/inch) silk bolting cloth. Considering both catching
ability and filtering efficiency, this mesh size was found to be somewhat
preferable to #4 (62 meshes/inch) silk and much preferable to #10 (109
meshes/inch) silk. The Great Lakes plankton large enough to be retained by
this silk is mostly limited to crustaceans. (2) It was determined that
the optimum speed for silk to pass through the Recorder in Lakes Michigan
and Huron is the same as in the marine Recorder survey, approximately 4
inches of winding for every 10 miles of towing. For Lake Erie the plankton
is much more abundant and the winding speed should be much faster. (3) As
in the marine survey, the optimum towing depth for the Recorder in the Great
Lakes is 10 m. The plankton at this depth is representative of the upper
layers and shows a comparatively low amount of variability in abundance
throughout the upper 10 m.

Objective 2

To determine and explain the distribution patterns of ten Great Lakes
calanoid copepods.

Results: The geographical distribution of the ten calanoid copepods
was determined by a synthesis of previously published information and the
collection of new datao Six species occur in each of the Great Lakes:
Diaptomus ashlandi^ Do minutus^ D, oregonensis ^ D. sicilisj Episahura
laaustrisj and Lirmooalanus maorurus. Seneoella oalanoides occurs in all
the lakes but Erie; Eurytemora af finis in Lakes Ontario, Erie, and Michigan;
D. sioiloides in Ontario and Erie; and D. reighardi only in Erie. D. sioilis
and L. maarurus are more abundant in the upper lakes, and D. oregonensis is
more abundant in the lower lakes «

A comparison of the relative abundance of diaptomids in Lake Michigan
in 1954-55, 1964 and in Lake Erie in 1956-57 shows that D. oregonensis was
most abundant in Lake Erie in 1956-57, and D. sioilis in Lake Michigan in
1954-55 o The season of maximum abundance of a species was generally earlier
in Lake Erie than in Lake Michigan.

Detailed results of this study are presented in Robertson (1966).

Objective 3

To develop a method for identifying the sex and stage of copepodites of
six species of Great Lakes diaptomids.

Results: Means of identifying the Great Lakes diaptomid copepodids
were developed by comparing the armature of all the appendages from each
copepodid stage of each species « Quite a number of differences in armature
were noted that varied only with stage and not with either species or sex.
A few differences in armature were noted that varied within a given stage as
to species but not as to sex. Finally, several differences were noted within

-2-

the last three stages that varied by sex but not species • The differences
noted above were presented in chart form and combined in a key to provide
means for identifying the Great Lakes diaptomid copepodids to species, stage,
and, for the last three stages, sexe

Results of this study have been reported by Czaika and Robertson (1968).

Objective 4

To demonstrate that data of substantial scientific value can be obtained
using a Research Ship of Opportunity.

Results^ A commercial vessel was used to gather biological samples on
its regular cruise from Detroit, Michigan to Bilboa, Spain. During the
cruise, samples were gathered for measurement of the amounts of particulate
organic matter and of dissolved organic matter, and for determination of the
composition of the zooplankton community. Some of the results from this
cruise have been used in comparing the distribution of organic matter in the
St o Lawrence Great Lakes. These results have shown that the concentration
of organic matter in the different lakes is closely correlated with the con-
centration of total dissolved solids and so with the relative state of eutro-
phicationo These studies have shown that Research Ships of Opportunity can
be used in either fresh or salt water and that the results obtained from a
Research Ships of Opportunity project can be of substantial scientific
interest o

The experiences gathered in planning, preparing for, and carrying out
the Research Ships of Opportunity project are presented in Robertson (1967),
the comparison of distribution of organic matter in the Great Lakes in
Robertson and Powers (1967) o

Objective 5

To study the changes in the composition of the zooplankton community

-3-

and in the amounts of particulate organic matter and dissolved organic matter
encountered in going from the fresh water of the Great Lakes out the Sto
Lawrence River and the Gulf of St. Lawrence to the salt water of the open
Atlantic Ocean.

Results: The zooplankton communities in the upper waters of Lakes
Ontario and Erie were found to be more diverse than the communities in com-
parable environments in the North Atlantic. The lakes, especially Lake Erie,
also had greater numbers of zooplankters per cubic meter.

Particulate organic matter and dissolved organic matter showed very
similar trends in abundance during the freshwater part of the cruise. Un-
fortunately, technical problems made it impossible to measure these parame-
ters during the saltwater part. Amounts of particulate organic matter were
found to be especially high in western Lake Erie and at the mouth of the
Sto Lawrence. It is suggested that these high values may be related to
favorable conditions for phytoplankton production in these two environments.

Detailed results of this study are presented later in this report.

Objective 6

To initiate a survey of the horizontal and seasonal distribution of the
plankton in Lake Michigan.

Results: A survey of the plankton of Lake Michigan, similar to the
marine plankton survey carried out in the North Atlantic by the Scottish
Marine Biological Association, has been initiated. Six tows of a Continuous
Plankton Recorder have been made between Muskegon, Michigan and Milwaukee,
Wisconsin. These samples are still being analyzed, and the results of this
study will be published latere

-4-

APPLICABILITY OF THE CONTINUOUS PLANKTON RECORDER
TO PLANKTON STUDIES IN LAKE MICHIGAN

The Continuous Plankton Recorder, initially developed by Hardy (1939),
has been used extensively to study the plankton of the North Sea and North
Atlantic (Glover 1962) o It is an instrument used to collect plankton during
the normal passage of commercial vessels* It samples at a depth of 10 ra
below the surface. The Recorders are adjusted in such a way as to maintain
this depth when being towed within a range of speeds from 10 to 18 knots.

Water enters the front of the Recorder through a 0.5-inch square opening
and flows into a 2 by 4-inch water tunnels A continuously moving band of
bolting silk (usually 60 meshes /inch) crosses this tunnel and filters out the
plankton. As the Recorder is towed, a propeller, exposed to the flow of
water, drives a winding mechanism that pulls the silk through the tunnel at
a predetermined rate. After emerging from the tunnel, the silk is covered
by a second band of silk to hold the plankton in place, and the two bands
are wound onto a storage spool in a tank containing formalin^

A long-term survey of the plankton of the North Sea and North Atlantic
is being carried out by the Scottish Marine Biological Association, Edinburgh
Laboratory, using this instrument. The survey began in 1931 and, with a
break during the Second World War, has continued to the present. Recorders
are towed roughly once a month over a series of standard routes by commer-
cial vessels and Ocean Weather Ships o For this survey the silk winding rate

3
is adjusted so that approximately 3 m of water are filtered for every 10

miles of towing o

After towing, the Recorders are returned to the Edinburgh Laboratory

where the silks are unrolled and cut into 4-inch blocks, each of which

-5-

represents approximately 10 miles of sampling • Colebrook (1960) has summa-
rized the most recent methods used to analyze these blocks. Estimates of
the numbers of the different plankters present are obtained, and these data
have been used as the basis of a large number of studies on the distribution,
systematics, and general ecology of the plankters of the area.

It would be very desirable to be able to carry out similar studies on
the plankton of the Great Lakes o The pelagic community is obviously an
immensely important part of the Great Lakes ecosystem. However, the diffi-
culties in collecting large numbers of samples in a regular manner have
largely precluded detailed studies on the offshore plankton of the Great
Lakes o Primarily, the lack of research ships and their expense when avail-
able have prevented the needed long-term, geographically extensive studies «

The objective of the present study was to adapt the Continuous Plankton
Recorder for sampling in the Great Lakes, so it would provide, as it has in
the Atlantic, the means by which a relatively inexpensive survey of the
plankton could be conducted. A large number of commercial vessels ply the
Great Lakes, so the opportunity to develop an extensive plankton survey is
present o

Before the initiation of this contract, the principal investigator spent
two years in the Edinburgh Laboratory becoming thoroughly familiar with the
use of the Recorder and methods for analyzing the samples it collects. It
was concluded that adaptation of the Recorder to plankton sampling in the
Great Lakes environment would require consideration of the following prob-
lems: (1) selection of a silk with a suitable mesh for use in sampling the
Great Lakes plankton, (2) determination of the optimum speed at which the
silk should pass through the Recorder, and (3) determination of the optimum
depth for towing the Recorder o

-6-

Selection of a Suitable Silk

The marine plankton survey uses Recorders equipped with bolting silk
having 60 meshes per incho It is assumed that this silk retains a major
proportion of the larger organisms, such as Copepoda, Cladocera, Pteropoda,
and Chaetognatha, and enough of the smaller forms to indicate their areas of
greater abundance. The Great Lakes plankton has a much smaller number of
major taxonomic groups than the marine plankton. Only the crustaceans and
the relatively rare fish larvae approach the size of the larger marine zoo-
plankters. It was decided that, for use in the Great Lakes, it would only
be possible for Recorder sampling to provide a representative picture of the
distribution of the crustaceans. For the smaller forms such as rotifers,
protozoans, and phy top lank ters, the best that could be expected would be data
similar to that obtained for the smaller marine forms.

In adapting the Recorder for use in the Great Lakes, initial considera-
tion was given to continuing the use of the 60 meshes per inch silk. However,
as the planktonic crustaceans in the Great Lakes tend to have a smaller
average size than their North Atlantic relatives, and as Robertson (in press)
has shown that many of the young stages of the smaller species even in the
North Atlantic escape this silk, it was decided to investigate the possibil-
ity of using a finer silk.

To study the feasibility of using a finer silk, a series of tests was
conducted to compare the filtering and plankton- catching abilities of
several silks. Dufour silk bolting cloths with 62 (#4), 82 (#7), and 109
(#10) meshes per inch were compared. No bolting cloth exactly comparable
to the 60 meshes per inch silk used in the marine survey was available, but
it was felt that the #4 silk was close enough to be considered the same for
all practical purposes «

-7-

Double bands of silk were prepared of each of the three mesh sizes as
described by Hardy (1939). They were made of sufficient length for two
hours of towingo The three bands, one of each mesh size, were then glued
together and loaded in a Recorder. This Recorder was towed for two hours so
a sample was obtained using the first mesh size. After two hours, the
Recorder was brought aboard and the joined bands of silk wound through the
Recorder until the next mesh size was ready for towing. The procedure was
repeated so a sample with the second mesh size was obtained and after this
a sample with the third mesh size.

This type of sampling was carried out on several different dates. The
tows were started a short distance out into Lake Michigan off the piers at
Grand Haven, Michigan. The tow with the first silk was made to the north
parallel to the shore for two hours, that with the second silk back toward
Grand Haven for two hours, and that with the third silk once again north for
two hours o Finally, the Recorder, but without any silk, was towed back to
Grand Haven for two hours o The order in which the different mesh sizes was
towed was altered for each series of tows so that a certain mesh size was
not always towed in the same direction.

The Recorder was fitted with a flow meter to monitor the relative
amounts of water passing through in two hours time using each of the silks
and with no silk in place. This flow meter was attached over the water exit
of the Recorder with a canvas sleeve that forced all the water leaving the
instrument to flow through the meter.

Meter readings for each date are presented in Table 1. It can be seen
at once that even with no silk in place the meter readings vary for the
different dates. These variations probably reflect the effect of environ-
mental conditions on the flow characteristics on different dates.

-8-

TABLE 1. Flow meter readings for two hours of towing
with #4 (62 meshes /inch), #7 (82 meshes/inch), and #10
(109 meshes/inch) silks and no silk in the Recorder.

Date

Number of

silk

No

#4

#7

#10

silk

13-IX-65

8240

5705

6210

8540

5-X-65

7660

6878

7175

7670

lO-XI-65

6345

6520

6650

7050

22-IV-66

6325

6250

5915

6770

30-VI-66

5430

5560

5260

7110

As expected, the reading for the tow when no silk was in place was
always the highest for a certain dateo Usually the readings were somewhat
lower than this but within 10 to 12 percent of the "no silk" one. For the
June towing all three silks show much lower readings, while for the September
towing only the readings for the #7 and #10 silks are much lower.

These much lower readings probably indicate clogging of the silks with
small organisms, mostly phytoplankton. Clogging of this type is common when
sampling plankton with bolting cloth in nets or other devices. The chance
of clogging increases as the bolting cloth gets finer, and this is one of
the major reasons the marine Recorder survey does not use a silk finer than
60 meshes per inch. Obviously, if the silk clogs, the filtering efficiency
is decreased and the number of organisms caught is decreased «

From these results it appears that clogging of Recorder silks of the
mesh sizes used here will be a problem only part of the time in the Great
Lakes, but that at times clogging will decrease the filtering efficiency by
as much as 30 to 40%.

-9-

On one of the two dates when clogging was observed, the #4 silk did not
clog while the others did. This observation suggests that the silk used in
the Recorder for a Great Lakes plankton survey should be as coarse as prac-
tical, to minimize cloggingo However, usually the #4 had almost the same
meter reading as the other two silks so its use in preference to the others
will only make an appreciable difference occasionally.

The tows described above were also used to compare the plankton-catch-
ing abilities of the three mesh sizes. A representative fraction of the
zooplankton caught on each of the silks was identified to allowed compari-
sons .

Identification of the zooplankton on the silks was carried out in a
manner modified from that used in the marine survey explained by Colebrook
(1960). After a band of silk had been towed, it was separated into three
blocks by cutting it where it had been glued together. A staggered micro-
scope traverse was taken across both the filtering and the covering silks of
each block, and all the crustaceans that were observed using the low power
objective (43.75X) were picked off. These animals were identified following
the keys in Edmondson (1959). In some cases such large numbers of animals
were picked off that it was necessary to limit the identifications to only a
certain known fraction. The fraction for counting was obtained by splitting
the sample once or twice using a Folsom Plankton Splitter.

Results of these identifications are presented in Table 2. Identifica-
tions were made on the tows for every date except October 5, 1965. This
sample was omitted to decrease the time and effort expended in analysis.
Samples from September and November were analyzed to give a picture of fall
conditions o

Comparisons of the plankton caught on the different silks on the same

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TABLE 2. Comparisons of the abundance ( individuals /m ) of crustaceans
caught in a Continuous Plankton Recorder using y/4 (62 meshes/inch), #7 (82
meshes / inch) , or #10 (109 meshes/inch) bolting cloth on four dates in Lake
Michigan.

#4

#7

#10

13-IX-65

Cladocera

Aliquot

1/4

Daphnia retroaurva

D. longiremis

D. gateata mendotae

Bosmina tongirostris

B. coregoni

Leptodora kindti

Diaphanosoma braohyumm

Ho lopedivm gibberum

Unidentifiable Daphnia

Unidentifiable Bosmina

Unidentifiable cladocerans

131

314

88

4

44

11

80

73

4

69

29

18

4

4

77

47

4

29

Total Cladocera

150

690

190

Cyclopoida

Cyclops bieuspidatus adults
Tropocy clops prasinus adults
Immature copepodids
Unidentifiable cyclopoids

11

208

58

4

11

117

26

756

628

47

44

Total Cyclopoida

41

1022

847

Calanoida

Diaptomus oregonensis adult males

adult females
D. ashlandi adult males

adult females
D. minutus adult males

adult females
Immature diaptomid copepodids

Total Diaptomus

Eurytemora af finis
Epischura lacustris
Unidentifiable calanoids

Total Calanoida

26

58

11

4

7

22

7

7

15

7

7

11

219

1394

1504

277

1503

1519

4

84

4

15

4

22

15

365

1533

1549

-11-

TABLE 2 continued

Miscellaneous

Unidentifiable copepods

Nauplii

Cladocera embyros

Total Miscellaneous

#4

#7

#10

66

7

18

44

11

7.

95

44

Total all crustaceans

563

3340

2630

lO-XI-65

Cladocera

Aliquot

Daphnia retroourva
Do gdleata mendotae
Bosmina longirostris
Bo ooregoni
Leptodora kindti
Unidentifiable Daphnia
Unidentifiable Bosmina
Unidentifiable Cladocera

Total Cladocera

1/2

183

1/4

512

1/2

15

29

7

15

7

73

51

66

234

29

7

7

73

146

22

15

15

116

Cyclopoida

Cyclops bicuspidatus adults
Tropoayalops prasinus adults
Immature copepodids
Unidentifiable cyclopoids

Total Cyclopoida

15

29

22

29

29

87

788

1190

15

402

846

1256

Calanoida

Diaptomus oregonensis adult males

adult females
D. ashlandi adult males

adult females
D. minutus adult males

adult females
D^ sioitis adult males

adult females
Immature diaptomid copepodids

22

73

7

44

15

15

15

73

102

44

37

15

22

7

7

307

292

299

-12-

TABLE 2 continued

#4

#7

#10

Total Diaptomus

Episohura laaustris
Unidentifiable calanoids

Total Calanoida

497

29

526

512

15

527

387

7

394

Miscellaneous

Unidentifiable copepods

Nauplii

Cladocera embyros

Total Miscellaneous

15

15

15

15

15

15

30

Total all crustaceans

1126

1900

1796

22-IV-66

Cladocera
Total Cladocera

Aliquot

1/2

1/2

Cyclopoida

Cyclops bicuspidatus adults
Immature copepodids
Unidentifiable cyclopoids

Total Cyclopoida

467

365

69

73

58

44

7

540

423

120

Calanoida

Diaptomus oregonensis adult males

adult females
D. asKlandi adult males

adult females
D. minutus adult males

adult females
Bo sioiUs adult males

adult females
Immature diaptomid copepodids

22

7

7

29

7

29

44

44

7

15

73

7

37

95

18

7

4

-13-

TABLE 2 continued

#4

#7

#10

Total Diaptomus

Limnooalanus maarurus
Unidentifiable calanoids

Total Calanoida

132

7
15

154

284

22

306

36

36

Miscellaneous

Nauplii
Total Miscellaneous

_0

15
15

Total all Crustaceans

694

744

163

30-VI-66

Cladocera

Daphnia tong-iremis
Bosmina longirostris
B. covegoni
Unidentifiable Bosmina

Total Cladocera

Aliquot

1/4

74

1/4

15

15

15

15

37

15

73

7

29

117

18

220

62

Cyclopoida

Cyclops bicuspidatus adults
Immature copepodids
Unidentifiable cyclopoids

Total Cyclopoida

438

569

55

642

2132

245

7

1080

2701

307

Calanoida

Diaptomus oregonensis adult males

adult females
D. ashlandi adult males

adult females
D. minutus adult males

adult females
Immature diaptomid copepodids

~14~

73

15

7

15

29

248

131

117

73

15

44

4

117

204

33

TABLE 2 continued

#4 #7 #10

Total Diaptomus 658 423 44

Episohura laaustris 15

Unidentifiable calanoids 15

Total Calanoida 688 423 44

Miscellaneous

Nauplii 15 15 _j^

Total Miscellaneous 15 15 18

Total all Crustaceans 1857 3359 431

date are very rougho The three silks compared from each series of towings
were towed at slightly different times and only over approximately the same
patho As zooplankton distributions are notoriously patchy both spatially and
temporally, differences in the quality and quantity of zooplankton on the
different silks may as well be attributed to differences in the plankton
assemblages sampled as to differences in the catching abilities of the dif-
ferent silks o However, four sets of comparisons were analyzed. It is assumed
that most differences due to factors other than the catching abilities of the
silks will tend to balance out over the four comparisons and that any very
obvious and extensive differences are probably due to the different plankton-
catching abilities of the different silks.

A quick examination of Table 2 shows one outstanding fact. The #7 bolt-
ing cloth catches more than either of the other silks in the great majority
of cases« For each of the four series of tows, the #7 silk caught the

-15-

largest total number of zooplankterso Even considering the different organ-
isms separately, the #7 silk almost always had the largest catch. Occasion-
ally, the #4 silk caught more of one of the larger organisms, such as one of
the species of adult calanoids, or the #10 silk caught more of one of the
smaller organisms, such as the immature cyclopoids or the Tropoay clops
prasinus adults, but generally the #7 silk caught the most.

It is not surprising that the #7 silk usually catches more than the #4
silk, for it has finer meshes and so will let fewer individuals through o In
the case of organisms that are too large to go through even the 7/4 silk,
this reasoning no longer holds o Thus, as was observed, the superior catching
ability of the #7 silk would not hold for the largest animals o

Much more surprising is the observation that the #7 silk usually catches
larger numbers of the different zooplankters than the #10 silk. Only for the
very smallest organisms, which almost entirely escape the #7 silk, is this
untrueo At this time it is impossible to explain why the finer mesh #10
silk catches so few animals. It could be that this silk is so fine that it
does not filter the water as easily as the other silks* This difficulty in
filtering might tend to push water ahead of the Recorder and so warn the
animals of the instrument's approach. However, the flow meter readings do
not indicate any appreciable difference in water filtered between the #10
and #7 silks «

The results in this section leave little doubt as to which of these
mesh sizes is preferable for use in a Recorder survey on the Great Lakes
planktono While the #4 silk is somewhat better with regard to avoiding
clogging, the #7 silk is by far the best for catching the crustaceans o Only
for the very largest animals would the #4 silk be of much use^ The #10 silk
is unsatisfactory both with regard to plankton-catching ability and filter-
ing efficiency.

-16-

Determination of Silk Winding Speed

The rate at which the bands of silk are wound through the Recorder in
relation to the amount of towing can be varied by altering the pitch of the
blades of the propeller that drives the winding mechanism. The faster the
winding rate, the lower the chance of clogging; for the faster the silks are
wound, the less time any part of the filtering silk is exposed in the water
tunnel o Yet, the storage spool in the Recorder can only accommodate so much
silk, so if the silks are wound on at a fast rate they will soon fill the
storage spool* When the spool is full, the Recorder must be brought aboard
and reloaded with fresh silks after removing the towed silks.

In the marine survey the blades of the propeller are set so that approx-
imately 4 inches of silk is wound on the storage spool for every 10 miles of
towing. This rate is a compromise in that it allows towing for up to 600
miles without changing silks and yet keeps the amount of plankton on the
silks low enough so that clogging is seldom a serious problem (Hardy 1939) o
There are usually appreciable numbers of crustaceans on a block of silk from
the marine survey, but not so many as to completely cover the block and make
analysis difficult o

It was decided to attempt to set the winding rate of the Recorder in
the Great Lakes so as to obtain quantities of plankton on the silks roughly
comparable to the quantities obtained in the marine survey. Although other
zooplankters commonly occur in the marine survey , crustaceans and specifi-
cally copepods make up the bulk of the animals found on the typical silk, as
in the Great Lakes o The total number of copepods of all species observed
while traversing each sample block is routinely counted in the marine survey,,
Colebrook and Robinson (1965) report on these counts. Their data indicate

that 100 to 500 copepods are usually seen on a transect. That is approxi-

3
mately 1,300 to 6,500 copepods per m .

-17-

Table 2 shows that the total numbers of crustaceans found in Lake
Michigan on test tows of the Recorder with #7 silk are within the range found
in the marine survey. This result was obtained with the winding rate set,
as in the marine survey, at approximately 4 inches for each 10 miles of
towing. The silks obtained in these tests looked similar to the usual marine
silks in amount of the silk covered by plankton and were comparable in ease
of counting to the marine silks. Thus, it seems that the quantity of plank-
ton in Lake Michigan caught by the Recorder is roughly the same as that
usually obtained in the North Atlantic, and so the winding rate should be
set the same.

A preliminary study was conducted that can be used to determine whether
the winding rate that was decided upon for Lake Michigan would also be useful
in other Great Lakes« Test runs with the Recorder were made in Lakes
Michigan, Huron, and Erie. These tests were' conducted through the coopera-
tion of the U. S. Bureau of Commercial Fisheries, who made available their
research vessel CISCO. A Recorder was towed' during August 1963 at a depth
of 10 m for 100 miles in Lake Michigan, 81' miles in Lake Huron, and 69 miles
in Lake Erie. These studies were conducted before it had been determined
that #7 (82 meshes/inch) silk was' preferable for' Great Lakes work, and so
60 meshes per inch silk was used. The samples were analyzed by the methods
lased in the marine Recorder survey (Colebrook 1960). These analyses were
carried out at the Edinburgh Oceanographic Laboratory during the author's
stay there.

One 4-inch block of silk from each lake was analyzed, and the results
are given in Table 3. The winding rates in Lakes Michigan and Huron were
approximately 4 inches per 10 miles of towing, as in the marine survey.
These blocks had somewhat less plankton than the typical marine block.

-18-

TABLE 3o Comparison of the numbers of several

crustaceans (individuals /m-^) caught in Lakes

Michigan, Huron, and Erie in August 1963 using
the Continuous Plankton Recorder •

Lake

Animal

Erie

Huron

Michigan

Cyclopoids

3450

285

64

Diaptomus

4250

326

51

Daphnia

4250

150

230

Bosmina

1000

109

345

Ceriodaphnia

700

Diaphanosoma

1750

Leptodora

13

Holopedium

„«

408

38

Polyphemus

^~.^

13
1304

13

Total crustaceans

15400

741

however, the block from Lake Michigan also had less total animals than found
on the #7 silks discussed previously^ The coarse silk used in these prelim-
inary runs probably allowed the escape of a large number of individuals. As
the quantities of crustaceans caught in Lake Huron and Michigan were roughly
similar, it seems likely that a winding rate of 4 inches per 10 miles would
be appropriate for both lakes o

As can be seen from Table 3, the block from Lake Erie had many more
animals than were found from Lakes Michigan and Huron. Because it was
already known that Lake Erie had high concentrations of zooplankters, the
winding rate had been set to be much faster in this lake than in the other
two lakes. Even so, with the rate at 4 inches per 1.68 miles of towing,

-19-

the silks were thickly covered with plankton, and it seems likely that fil-
tering efficiency was decreased. These blocks were covered at least as much
as the most heavily covered blocks from the marine survey. If #7 silks had
been used, even more animals would have been caught.

These results indicate that a much faster winding rate should be used
for Recorder tows in Lake Erie than in the other lakes. A rate of 4 inches
per 1 mile of towing or even faster seems called for when using #7 silk.
However, as the Recorder is presently constructed, the rate used in Lake
Erie during these preliminary tows is about the fastest possible. It may be
that a change in the gear reduction ratio between the propeller, exposed to
the water flow, and the storage spool would be necessary if the Recorder
were to be used for an extensive survey in Lake Erie.

Determination of Towing De-pth

The samples for the marine Recorder survey were all taken from a depth
of 10 m, the depth chosen as most likely to give consistent results (Hardy
1939) o Studies conducted by the Edinburgh Laboratory indicated this depth
as having the minimal seasonal and diurnal variations in vertical distribu-
tion of plankton in the North Seao The depth of towing can be controlled,
within limits, by controlling the amount of wire between the ship and the
Recorder o The towing depth for a Great Lakes plankton survey could be varied
from 10 m if there were reasons indicating some other depth would be prefer-
able.

To make an intelligent decision as to what towing depth would give the
most consistent results in the Great Lakes, it is necessary to have some idea
of the variations in vertical distribution of the Great Lakes plankters.
However, a study to give a picture of variations in vertical distribution
was beyond the scope of the present research. Fortunately, Wells (1960)

-20-

presents data on the abundance of the planktonic crustacean species of Lake
Michigan at different depths on several different dates. His data have been
analyzed to determine what depth would be optimum for towing the Recorder.

On ten dates in 1954 and 1955, Wells took a series of horizontal plank-
ton tows at different depths with a calibrated Clarke-Bumpus plankton sampler.
These samples were analyzed so that his paper includes a table for each
common species showing its abundance at a series of depths for each date.
For the purposes of the present study, it was impractical to study the verti-
cal distribution of each individual species. Instead, the data have been
combined to give the abundance of the total crustacean plankton at each depth
on each sampling date^ These totals are presented in Table 4.

The results in this table show consistent differences among depths in
abundance o Generally, the deeper samples had fewer individuals than the
shallower oneso There seem to be consistent differences among depths in the
amount of variation in abundance during a sampling period. The surface sta-
tion tends to have more variability in abundance during a sampling period
than the other depths.

To give a more precise picture of these differences, the data for each
sampling period have been averaged and the coefficient of variability within
the sampling period calculated for each depth (Table 5). It will be noted
from the table that the 10-m depth has relatively large numbers of animals
and relatively low coefficients of variability. Sampling at this depth
should provide samples representative of the conditions in the upper waters
with the minimum distortion of individual results due to variability in
vertical distributiouo Thus, there seems to be no reason to change the
Recorder towing depth from 10 m for a survey in the Great Lakes.

-21-

3
TABLE 4o Abundance (individuals /m ) of the total crustacean plankton at

different depths in Lake Michigan on a series of sampling dates. These data
were obtained by summing the individual species values for abundance pre-
sented in Wells (1960).

Dj

ate

Depth

t (m)

Ut

Surface

5

10

20

30

40

June 6-

-7, 1954

2:00

p.m.

3,820

—i-^

— ^i.

4:00

p.m.

20

2,338

— __

^^_

i-.__

6:00

Pom©

163

2,561

—

.-.—

_.—

8:40

p.m.

2,743

1,967

— — _

— .-.

_«._

10:00

Pome

7,142

___

2,337

.^-.

«■— ■»

12:00

p.m.

4,283

1,751

—

-.-._

■»»

1:00

aoTCio

2,311

June 2?^ 28

10:00

Pomo

_-_

5,537

i...

M_^

12:00

p.m.

9,274

3,206

1,971

586

i-.__

2:00

aomo

8,799

2,347

— ._

4:00

a<,mo

6,745

6,546

2,542

1,837

July 16^ 17

7:00

p.m.

3,999

5,218

5,973

2,468

992

9:00

p.m.

16,038

5,164

4,261

2,185

1,220

11:00

p.m.

22,850

6,872

4,629

1,782

893

1:00

aomg

12,847

7,568

4,998

1,518

1,053

3:00

a.m.

13,430

9,289

4,653

1,922

863

4:30

a^mo

5,506

11,151

3,520

1,409

918

August

7

5:30

Pomo

365

12,857

5,423

1,599

1,693

7:45

p.m.

7,702

14,356

3,904

1,711

949

9:30

Pomo

13,593

12,431

4,120

1,787

1,519

11:00

p.m.

16,434

7,785

3,175

1,358

1,591

August

27

5:45

Pomo

76

2,680

4,789

2,329

7:30

p.m.

475

3,232

4,050

831

9:00

p.m.

8,654

2,129

3,934

1,796

1,476

11:00

Pomo

5,531

2,855

6,176

853

Ootohei

' 7

5:15

Pomo

1,778

6,682

3,187

644

766

7:00

p.m.

7,502

8,974

2,026

734

9:15

Novembe

p.m.

'■r 18

6,001

6,719

2,158

1,116

532

4:30

p tin.

1,896

7,019

1,771

944

640

6:00

p.m.

11,421

9,348

1,132

1,595

8:00

PoIDo

8,814

951

750

10:00

Poin,,

11,216

3,600

2,216

911

-22-

TABLE 4 continued

Depth

(m)

Date

Surface

5

10

20

30

40

June 50^ 1955

6:00 p.m.

917

2,224

2,383

3,918

4,241

893

8:30 p.m.

2,809

2,857

2,181

2,809

1,595

1,551

11:30 Pom.

3,329

5,473

2,768

2,600

1,147

510

July 24

4:15 p»m.

577

4,873

10,050

9,176

1,543

364

6:15 p.m.

1,605

3,133

5,964

3,427

514

244

8:15 p.m.

3,295

4,437

6,124

4,103

404

10:45 Pom,

7,882

7,037

4,877

2,873

387

150

October 2

2:00 p.m.

210

4,393

9,330

4:20 p.m.

583

8,009

7,171

6,489

1,124

6,045

6:30 p.m.

3,737

9,249

5,991

3,008

1,516

2,016

8:20 Pom,

4,998

10,656

6,330

2,043

1,102

494

10:30 pomo

5,738

3,165

1,079

193

TABLE 5. The mean abundance (x) , variance (s ), standard deviation (s) , and co-
efficient of variability (CV) of total crustacean plankton at different depths at a
series of dates in Lake Michigan. These values are based on data of Wells (1960).

Date

Surface

Depth (m)

10

20

30

40

1954

June 6 J 7

s"
s

CV=

100s

X

June 27 J 28

2,380

7,097,279

2,664

111.93

2,462

527,102

726

29.49

X

s2
s
CV

8,273
1,806,731
1,344
16.25

5,096

2,287

1,212

2,934,541

84,241

782,500

1,713

290

885

33.61

12.68

73.02

-23-

TABLE 5 continued

Date

Surface

10

Depth (m)

20

30

July 16, 17

X

s
CV

August 7

X

12,445
48,358,028
6,954
55,88

9,524

s
CV

50

,503,942
7,107
74.62

August 27

X

s
CV

17

3,684
,142,551
4,140
112.38

October 7

X

s2
s
CV

8,

5,094
,808,485
2,968
58»26

November 18

X

s2
s
CV

19,

8,337
,837,902
4,454
53o42

1955

June 30

X

s2
s
CV

1,

2,352
,611,303
1,269
53.95

July 24

X

s
CV

3,340
10,425,394
3,229
96.68

3,518
2,966,691
1,722
48.95

4,870
2,633,519
1,623
33.33

2,444
88,933
298
12.19

6,754
5,135,915
2,266
33.55

3,109
501,781
708
22.77

4,895
8,399,244
2,898
59.20

2,328
2,795,810
1,672
71,82

815
401,885
634
77.79

40

7,544

4,672

1,881

990

5,516,462

659,422

160,604

17,519

2,349

812

401

132

31„14

17.38

21.32

13.33

11,857

4,156

1,614

1,438

8,051,887

877,483

35,033

111,372

2,838

937

187

334

23.94

22.55

11.59

23.23

2,724

4,737

2,063

1,053

210,395

1,063,401

142,044

134,107

459

1,031

377

366

16.85

21.76

18.27

34.76

7,458

2,457

831

649

,723,277

404,031

62,802

27,377

1,313

636

251

165

17„61

25.89

30.20

25.42

6,656

1,706

1,100

695

8,358,885

296,901

109,094

6,050

2,891

545

330

78

43o43

31.95

30.00

11.22

985
277,223
527
53.50

291
13,396

116
39.86

-24-

TABLE 5 continued

Date

Depth

(m)

Surface

5

10

20

30

40

October 2

X

s2
s
CV

3,053
6,410,914
2,532
82.93

7,094
10,225,384
3,198
45o08

7,206
2,252,067
1,501
20.83

3,847
5,469,251
2,339
60.80

1,205
43,256
208
17.26

2,187
7,251,897
2,693
123.14

-25-

A COMPARISON OF SOME BIOLOGICAL PROPERTIES SAMPLED ON THE CRUISE
OF A MERCHANTMAN FROM DETROIT, MICHIGAN TO BILBOA, SPAIN

As an inexpensive means of collecting oceanographic and limnological
data, it has been suggested that commercial vessel during their regular
passage might be used as collecting platforms (Research Ships of Opportunity
concept) o The feasibility of this concept has been tested both in the
Atlantic and the Pacific, and the results have shown that it holds great
promise. During the summer of 1966 the feasibility studies were expanded to
include a cruise that was partially in fresh and partially in salt water.
The Principal Investigator participated in this cruise and has published the
experiences obtained in planning, preparing for, and carrying out the project
elsewhere (Robertson 1967).

The waters of a river system change gradually as they flow to the sea
and then change abruptly as they meet the sea and flow out the estuary. For
practical reasons, very few studies have been conducted to study these
changes in a large river system, starting a great distance inland and con-
tinuing out into the open oceano The Research Ships of Opportunity project
mentioned above provided an excellent opportunity to conduct such studies.
The scientific objective of the project was to conduct a comparison of cer-
tain environmental properties along the line of cruise.

The properties selected for study were the amount of particulate or-
ganic matter, the amount of dissolved organic matter, the composition of the
zooplankton community, the temperature, and the conductivity. These were
selected because it was felt they would facilitate meaningful comparisons
among the biological communities in the different envirdnmerits and because
they lent themselves to relatively simple measurement on the merchant vessel.

-26-

The results of the measurements, with a brief comparison of the different
environments, are presented here. Part of this information has been used
previously in a comparison of the five St. Lawrence Great Lakes (Robertson
and Powers 1967).

Temperature

Sampling procedures and stations used for this study have been explained
in Robertson (1967) o Briefly, however, water samples from a depth of 24 ft
were drawn from the main injection line of the ship once every two, three,
or four hours while underway, depending upon the rate at which the environ-
ment was changing. The temperature of each water sample was measured as soon
as it was taken o These values have been plotted versus sample number in
Figure lo

Temperatures during the freshwater part of the cruise were generally
relatively high, with the highest temperatures occurring in the shallow,
western end of Lake Erie. Lake Ontario had somewhat lower temperatures,
with the sample from the middle of the lake being by far the coolest. At
the entrance to the Sto Lawrence from Lake Ontario, the temperature was
high, while the temperatures down the rest of the river were somewhat lower
and relatively constant « The largest change in temperature during the cruise
was that encountered in going from fresh to salt water at the mouth of the
St. Lawrence 3 Cold water comes into the Gulf of St. Lawrence through the
Strait of Belle Isle between Newfoundland and the mainland and sometimes
also from around Newfoundland. This water keeps especially the northern
part of the Gulf of Ste Lawrence and the St. Lawrence estuary cool. As we
went out from the mouth of the St« Lawrence, the temperature rose until we
got to the warm waters coming up from the south in the Gulf Stream. The
temperature then stayed relatively constant for the rest of our cruise.

-27-

20 30 40

SAMPLE NUMBER

FIG. 1. Water temperature plotted by sample number for a cruise from
Detroit, Michigan to Bilboa, Spain.

-28-

However, there was a noticeable, though slight, tendency for decreasing tem-
peratures as we proceeded eastward in the North Atlantic Drift. This cool-
ing tendency was reversed in the Bay of Biscay as we approached the Spanish
coast, by a distinct rise in temperature.

Conduotivity

The specific conductance compensated to a temperature of 25°C was mea-
sured on each sample, using a conductivity bridge. There is a great differ-
ence between the values for fresli and those for salt water, and so the
results from these environments have been plotted separately versus sample
number (FigSo 2, 3).

The conductivity values start out relatively low, with the two values

-4
from western Lake Erie being around 2c75 x 10 . Then the values Jump up

-4 -4

to between 3o30 x 10 and 3o45 x 10 for most of the rest of the fresh-

x^^ater part of the cruise. Only the last couple of measurements at the mouth

of the river again fall to lower values. A suggestion as to the cause of

these lower values at the start and end of the freshwater part of the cruise

will be discussed in the following subsection.

Excluding these lower values at the mouth, it will be noted that the
tendency was for a slight increase in conductivity as we progressed down-
streamo Intuitively^ it would seem reasonable to expect the quantity of
dissolved salts to increase as the waters flow past such metropolitan centers
as Cleveland, Buffalo, Toronto, and Montreal. Why a more noticeable increase
in conductivity was not noted is not evident at this time.

The saltwater part of the cruise shows, in general, increasing conduc-
tivity (expressed as salinity) as we proceeded across the Atlantic. The
lowest value of about 19 *^/00 was found in the first sample in salt water,
where the influence of the river water was still strongly felt. After this,

-29-

3,40

o

E 3.30

I

o

X

111
u

u

D
Q
Z

O

u

3.20

3.10

3.00

U

ui

5 2.90

U
0.
(/)

2.80

2.70

PAST
MONTREAL

LAKE
ONTARIO

ST. LAWRENCE
SEAWAY

J L.

_L

SAM RLE

10
NUMBER

15

20

FIG. 2. Specific conductance plotted by sample number for the freshwater
part of a cruise from Detroit, Michigan to Bllboa, Spain.

-30-

40
SAMPLE

NUMBER

FIG. 3. Salinity plotted by sample ntimber for the saltwater part of a
cruise from Detroit, Michigan to Bilboa, Spain.

-31-

the values rose and fell to some extent, but, in general, they increased
until we got into the North Atlantic Drift. This rising trend is due to the
decreasing influence of land drainage and of Labrador Current water and to
the increasing influence of Gulf Stream water from the south. This water
has a higher salinity than the Labrador Current water, which comes down from
the north, so the salinity increases as the Gulf Stream influence becomes
more strongly felt« For the rest of the cruise, the salinity stayed at rel-
atively high values around 35 "^/OO, except just off the Spanish coast where
it fell somewhat, again probably due to the influence of land drainage. It
is possible to separate the major marine environments encountered during the
cruise by plotting salinity versus temperature (Fig. 4).

Partioulate Organic Matter and Dissolved Organic Matter

The values for particulate and dissolved organic matter have been
plotted together in Figure 5 because the two properties show such similar
trends. Only the values for the freshwater part of the cruise are treated
hereo For measuring particulate organic matter in fresh water we used the
method of Robertson and Powers (1965) o This method entails filtering the
water through a 0o8y, pre-weighed membrane filter, reweighing the filter
after drying, and considering the difference between the two weights as the
weight of particulate matter. The filter plus particulate matter was then
ashed and the weight of ash subtracted from the particulate matter value to
give an estimate of particulate organic matter. (The filter is essentially
ash-free. )

It had been hoped to follow this same procedure for measuring the par-
ticulate organic matter in the salt water, and, in fact, such measurements
were madeo However, these measurements have not been included here because
it was found that in salt water the filters gained weight that could not be

-32-

26

22

U 18

UJ
ct:

ct:
u

CL
UJ

6

SPANISH COAST

OPEN ATLANTIC

GULF OF
ST. LAWRENCE

EAST OF
GRAND BANKS

GRAND BANKS

SOUTH OF
NEWFOUNDLAND

_L

19 21

23

25 27 29

SALINITY (%o)

31

33 35

F3LG. 4. A temperature-salinity diagram for the saltwater part of a cruise
from Detroit, Michigan to Bilboa, Spain.

-33-

5 10 15

SAMPLE NUMBER

20

FIG. 5. The amounts of particulate organic matter and of dissolved organic
matter plotted by sample number for the freshwater part of a cruise from
Detroit, Michigan to Bilboa, Spain.

-34-

attributed to particulate matter. This weight increase could not be elimin-
ated by repeated washings with distilled water. The gain in weight on ex-
posing the filters to salt water occurred even after the water had been fil-
tered as many as sixteen times, thus eliminating any possibility that the
weight gain could be caused by retention of particulate matter. It is pos-
tulated that some of the salt ions were adsorbed so strongly by the filters
that even repeated washing with distilled water would not cause their reso-
lution <>

Dissolved organic matter was measured by a dichromate oxidation method
following, with some modification, Maciolek (1962). The factor given by
Maciolek to enable the results to be expressed in terms of organic matter
has been used. Both particulate and dissolved organic matter were measured
in triplicate each time samples were taken. Samples for measuring dissolved
organic matter were not taken at the start of the cruise because the samples
had to be frozen for return to the laboratory, and the freezer could not be
connected to a source of electric power for the first few hours.

Results for the two properties show very similar trends. Values for
particulate organic matter were high in western Lake Erie, where dissolved
organic matter was not measured « The high values were probably due to the
wastes released into the western end of the lake by Detroit. These wastes
contain large quantities of settleable solids as well as high concentrations
of plant nutrients. The solids would be measured directly while the nutri-
ents would stimulate phytoplankton growth which would cause increased quan-
tities of particulate organic matter.

Both particulate and dissolved organic matter were relatively low in
the rest of Lake Erie and only somewhat higher in Lake Ontario. They were
about the same in the St. Lawrence as in Lake Ontario except in sample 13.

-35-

This sample was taken just downstream from what appeared to be a large paper
mill on the shore. The wastes from this mill could be the cause of the high
values for both properties at this one point in the river.

At the mouth of the river the values for both properties go up to very
high levels, possibly due to the waters of the river slowing down here as
the estuary begins o These waters have been enriched as they flow past
Montreal and other cities along the river but have been flowing too fast and
have been too turbulent for large populations of phytoplankton to develop «
Here, at the mouth, the river widens, and so it flows slowly enough for the
algae to take advantage of the nutrients « Also, with decreased turbulence,
the phytoplankters have a better chance of staying in the lighted, upper
water layers. A further contributing factor may be the layer of salt water
that flows well up the estuary. This underlying layer of high density water
causes the development of a stable two-layered system that further prevents
the algae from being carried into the deeper waters and out of the euphotic
zoneo

During the freshwater part of the cruise there seemed to be an inverse
correlation between amount of particulate organic matter and specific con-
ductance (Figo 6). If it is assumed that the areas of high particulate
organic matter are areas of phytoplankton blooms, then this increased organic
production may reduce the specific conductance by tying up some of the ions
in phytoplankton biomasso

Composition of the Zoo-plankton Communities

The zooplankton communities in Lakes Erie and Ontario and in the St.
Lawrence Estuary and the Gulf of St* Lawrence were sampled using the Contin-
uous Plankton Recorder o Maps showing the paths of towing are included in
Robertson (1967) o The Recorder and its use are described in the preceding

-36-

3.40

to

o 3.30L

3.20.

LU
U

^ 3.10.
<

U

Q

z 3.00.

O

U

• •

••

u

u
u

CL
CO

2.90.

2,80.

2,701

_L

0.0 1.0 2.0 3.0 4,0 5,0 6.0

PARTICULATE ORGANIC MATTER (mg/l)

FIG. 6. The relation between amount of particulate organic matter and
specific conductance for the freshwater part of a cruise from Detroit,
Michigan to Bilboa, Spain.

-37"

section of this report. For our tows the Recorder was fitted with 60 meshes
per inch silk, was towed at 10 m depth, and was set so that approximately 4
inches of silk was wound through for every 10 miles of towing «

The freshwater samples from Lakes Ontario and Erie were analyzed in our
laboratory. The towed silks were cut into blocks, each representing 10 miles
of towing, and the blocks numbered consecutively, with block #1 containing
the plankton from the first 10 miles o A staggered microscope traverse was
run across each odd-numbered block using the low power of a compound micro-
scope (43.75X), and all animals observed were picked off. On the freshwater
silks only crustaceans were observed. The other zooplankters, mostly roti-
fers and protozoans, are too small to be retained regularly by the 60 meshes
per inch silk, and even the ones that were retained were too small and incon-
spicuous to be noted during our traverse. The animals that were picked off
were identified and the results, converted to individuals per cubic meter,
are presented in Tables 6 and 7.

The samples from the St. Lawrence Estuary and the Gulf of St. Lawrence
were kindly analyzed by the Edinburgh Oceanographic Laboratory of the
Scottish Marine Biological Association. They treated these samples as part
of their regular survey of the plankton of the North Atlantic using their
standard methods (Colebrook 1960) o

An attempt has been made to compare the zooplankton communities sampled
during the cruise. While obviously very rough, this comparison has the
distinct advantage that the samples, from a wide variety of environments,
were all taken by the same method o

It had been planned to attempt to sample the zooplankton communities
all the way to Spain with the Recorder o However, the outboard end of the
cable parted at the towing eye and the Recorder was lost. Fortunately, it
has been possible to obtain substitute data for that part of the unsampled

-38-

TABLE 6e The abundance (individuals/m ) of crustaceans caught by the
Continuous Plankton Recorder in a tow in Lake Erie from Pointe aux Pins to
off the entrance to the Welland Canal «

Organism

Block No.

11

Cladocera

Daphnia galeata mendotae
D. vetroQurva
Bosmina ooregoni
Diaphansoma brachyumm
Leptodova kindti
Unidentifiable Daphnia
Unidentifiable Bosmina

8056 8616 8296 4104 1224 4416

40

120

224

440

80

112

24

24

24

136

64

32

40

32

56

72

16

24

32

48

40

56

320

176

240

56

88

216

8

16

16

Total Cladocera

8504 9008 8872 4872 1496 4832

Gyclopoida

Cyclops biouspidatus adults
Mesooy clops edax adults
Cyclopoid copepodids
Unidentifiable Cyclopoida

192

208

400

480

24

128

232

680

1160

704

80

160

448

640

1048

784

48

240

8

8

Total Cyclopoida

872 1528 2608 1976 152 536

Calanoida

Diaptomus oregonensis adults
Do ashlandi adults
Do siciloides adults
Do minutus adults
Diaptomid copepodids
Unidentifiable diaptomids
Eurytemora affinis

232

680

1032

712

144

160

24

8

8

8

72

104

96

40

8

8

120

352

208

184

16

56

32

56

48

8

8

Total Calanoida

480 1200 1392 952 176

224

Miscellaneous

Cladocera embryos
Nauplii

Total Miscellaneous

8

24

40

8

8

24

40

Total all Crustaceans

9864 11760 12912 7808 1824 5600

-39-

TABLE 7. The abundance (individuals/m ) of crustaceans caught by the
Continuous Plankton Recorder in a tow in Lake Ontario from off the entrance
to the Welland Canal to the entrance to the St. Lawrence River.

Organism

Block No.

11 13 15

Cladocera

Daphnia galeata mendotae
D. retroourva
Bosmina oovegoni
Bo longirostris
Leptodora kindti
Unidentifiable Daphnia
Unidentifiable Bosmina

32

8

8

8

16

168

24

80

8

8

88

118

160

440

72

32

16

8

32

16

8

16

16

8

24

24

8

24

24

16

16

24

Total Cladocera

192 160 32 16 104 134 200 712

Cyclopoida

Cyclops bieuspidatus adults
Cyclopoid copepodids

Total Cyclopoida

64

16

8

16

8

80

8

16

144

24 8

16

16

Calanoida

Diaptomus oregonensis adults
Diaptomid copepodids

Eurytemora af finis

Total Calanoida

80

8

56

8

8

32

8

40

136 16 8

32

8 40

Miscellaneous

Cladocera embryos
Nauplii

Total Miscellaneous

8

8

8

16

16

_0

8

8 8 16

8 16

Total all Crustaceans

480 176 64 40 136 174 216 784

-40-

cruise path up to the North Atlantic Drift. Recorder tows were made south
of Newfoundland, over the Grand Banks, and east of the Grand Banks within
two weeks of our cruise as part of the Edinburgh Laboratory's routine survey «
These data have kindly been made available by that laboratory and have been
included in the comparison «

The abundance values in the data from the Edinburgh Laboratory are only
approximate In their survey the abundance of an organism is estimated only
as far as a series of abundance ranges (Colebrook I960), However, Rae (1952)
has calculated a mean number for each of the ranges based on actual counts,
and these values have been taken as the abundance values for the purposes
of the present paper*

As a measure of diversity, the mean numbers of microcrustacean species
and of all zooplankter species per block have been calculated for each
environment (Table 8) . Only the zooplankters large enough to be retained
reasonably well by the 60 meshes per inch silk have been included. The
values from the marine environment may be somewhat underestimated because
the routine Recorder survey does not identify down to the species level in
most cases o Long experience with Recorder samples from the North Atlantic
has shown that, in most cases, only one species is present on a block from
any one of the groupings used in the identifications and it is believed that
we can consider the underestimation as relatively minor.

It will be noted that the freshwater environments have more species
than the marine. This is somewhat surprising for it is usually assumed that
diversity is less in fresh water. This rather anamolous situation probably
is caused to some extent by the paucity of plankton species found in the
upper waters of the North Atlantic compared to most other marine areas.
There seems little doubt that many more species are present in the North
Atlantic at other depths than those sampled, and this is almost assuredly

-41-

TABLE 8. The mean number per block of species of microcrustacea and of
total zooplankton species as well as the mean abundance per block of micro-
crustacea and of total zooplankton ( individuals /m-^) from a number of en-
vironments sampled by the Continuous Plankton Recorder.

Environment

Species of

micro-
crustacea

Total

species of

zooplankton

Abundance
of micro-
crustacea

Total abun-
dance of
zooplankton

Lake Erie

9o5

9.5

8295

8295

Lake Ontario

4.9

4.9

259

259

Sto Lawrence Estuary

lo2

1.4

20

20

Gulf of Sto Lawrence

lo9

3.4

111

113

South of Newfoundland

2ol

3.1

67

92

Grand Banks

1«7

3.8

35

139

East of Grand Banks

1.0

1.9

25

31

not true in the lakes o These results do suggest that caution should be
exercised in assuming marine environments are more diverse in species than
comparable freshwater ones*

The mean abundance of microcrustaceans and of all zooplankters per
block has also been calculated for each environment (Table 8.) The most
outstanding fact is the tremendous abundance of zooplankton in Lake Erie
compared to all the other environments « This may be attributable to high
phytoplankton productivity in this lake as suggested by the high particulate
organic matter values found in its western end. This high phytoplankton
production would furnish the food for large numbers of zooplankters.

-42-

REFERENCE S-^

COLEBROOK, J, M. 1960o Continuous plankton records: Methods of analysis,
1950-1959O Bull. Mar. Ecolo, 5:51-64.

> and G. A. ROBINSON^ 1965o Continuous plankton records: Sea-
sonal cycles of phytoplankton and copepods in the northeastern Atlantic
and the North Sea. Bullo Maro Ecol., 6: 123-139.

*CZAIKA, S. C. and Ac ROBERTSON o 1968. Identification of the copepodids of
the Great Lakes species of Diaptomus (Calanoida, Copepoda) . Proc. 11th
Confo on Great Lakes ReSo, p. o Internat. Assoc, for Great Lakes
Reso

EDMONDSON, W. T. (ed.). 1959o Fresh-water biology (2nd ed.). John Wiley &
Sons, InCo, New York, 1248 p.

GLOVER, Ro So 1962. The Continuous Plankton Recorder. Rapp. Proces-Verbaux
Reunions, Conseil Pernio Intern. Explo Mer, 153: 8-15.

HARDY, A. C. 1939o Ecological investigations with the Continuous Plankton
Recorder: Object, plan and methods o Hull Bull. Mar. Ecol. , 1: 1-57.

MACIOLEK, Jo Ao 1962. Limnological organic analysis by quantitative dich-
romate oxidation. Fisho Wildlife Serv. , Res. Rept. 60, 61 p.

RAE, Ko Mo 1952. Continuous plankton records: Explanation and methods,
1946-1949. Hull Bullo Maro Ecol., 3: 135-155.

^ROBERTSON, Ao 1966. The distribution of calanoid copepods in the Great
Lakeso Proc. 9th Conf. on Great Lakes Res., Univ. Michigan, Great
Lakes Reso DiVo , Pub. Noo 15: 129-139.

1967. Research Ships of Opportunity program: Project Neptune

Limnoso Univ. Michigan, Great Lakes ReSo Div. , Spec. Rep. No. 28, 25 p.

_____ (In press). Continuous plankton records: A method of study-
ing herbivore biomass with the Continuous Plankton Recorder. Bull.
Maro Ecol.

_^, and C. F. POWERS o 1965. Particulate organic matter in Lake

Michigano Proc. 8th Conf. on Great Lakes Res., Univ. Michigan, Great
Lakes Reso DiVo, Pub. NOo 13: 153-159.

, and Co Fo POWERS. 1967 o Comparison of the distribution of or-

ganic matter in the five Great Lakes. Univ. Michigan, Great Lakes Res.
Div., Spec. Rep. Noo 30: I-I80

WELLS, Lo 1960. Seasonal abundance and vertical movements of planktonic
Crustacea in Lake Michigano Fisheries Bull. Fish Wildlife Serv., 60:
343-369.

The asterisk indicates papers already published from this project.

-43-

Security Classification

DOCUMENT CONTROL DATA • K&D

(Security clm99iUcmtion ot titt9, body oi abstract and Indexing annotation mu9t b» mntmrmd wh»n thm ovrmll nport ia claaaiiiad)

1. ORIGINATING ACTI\/ITY (Corporato author)

The University of Michigan
Ann Arbor, Michigan

Za. REPORT SECURITY CLASSIFICATION

Unclassified

2 b. GROUP

3. REPORT TITLE

The abundance, distribution and biology of plankton in Lake Michigan with the
addition of a Research Ships of Opportunity Project

4. DESCRIPTIVE NOTiS (Tyfi9 of nport and inchaalva dataa)

Final Report

5. AMTHORCS) (Lmat nmma, Htat nama, iriiHal)

Robertson, Andrew

6. REPORT DATE

September 1968

7«. TOTAL NO. OF PAGES

76. NO. OF REFS

8a. CONTRACT OR GRANT NO.

Nonr-1224(53)

b. PROJECT NO.

NR 104-818

c.
d.

9«. ORIOINATOR*S REPORT NUMGERfS;

Great Lakes Research Division
Special Report No. 35

• *. g^JHER PMEPORT NOfJ;; (Anyoihatnumbmra thai

may ba aaalinad

10. AVAILABILITY/LIMITAtiON NOTtCCS

Distribution of this document is unlimited.

n. SUPPLEMENTARY NOTES

ia. SPONSORING MILITARY ACTIVITY

Office of Naval Research
Washington, D.C.

13. ABSTRACT

This report summarizes the results obtained from a study on the abundance,
distribution, and biology of plankton in Lake Michigan as well as from a
Research Ships of Opportunity cruise.

Modifications needed to adapt the Continuous Plankton Recorder for use in
the Great Lakes are presented in detail. The major change from the procedure
used in the marine Recorder survey on the plankton of the North Atlantic is the
use of a finer silk for filtering.

A detailed presentation is also made of the scientific results obtained
during a cruise aboard a Research Ship of Opportunity from Detroit, Michigan
to Bilboa, Spain. Studies were made on the changes in composition of the zoo-
plankton community as well as in the amounts of particulate organic matter and
dissolved organic matter encountered during this cruise. The diversity and
quantity of microcrustaceans were found to be greater in the lakes than in the
comparable marine environments. Particulate and dissolve^ organic matter follow-
ed very similar trends in relative abundance and were especially high in western
Lake Erie and at the mouth of the St. Lawrence River.

DD

FORM

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1473

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LINK A

nOLE

LINK B

ROLC

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ROLC

Research Ships of Opportunity
Zooplankton in Lake Michigan
Continuous plankton recorder
Identification of immature calanoids

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