THE NEARSHORE ZOOPLANKTON OF, LAKE- _ _ . MICHIGAN ADJACENT TO THE LUDINGTQN PUMPEDASTORAGE RESERVOIR Thesis for the Degree ef-MI S; MICHIGAN STATE UNIVERSITY WALTER e. DUFFY ’ 1975“ '. ‘ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\I 10467 4035 \\\\\\\\\\\\\\\\ WW I\\\\\\ 3_1293 ABSTRACT THE NEARSHORE ZOOPLANKTON OF LAKE MICHIGAN ADJACENT TO THE LUDINGTON PUMPED-STORAGE RESERVOIR BY Walter G. Duffy Inshore zooplankton distributions and densities at six stations near Ludington, Michigan were investigated from 29 April to 31 October, 1973 and from 10 May to 4 November, 1974. Samples were collected biweekly using a pump and net method. Distribution and abundance of major taxa (Cladocera, Cyclopoida, Calanoida, Rotifera, and copepod nauplii) in 1973 and 1974 and species in 1974 were investigated at six stations. In addition vertical distribution of species and total zooplankton at one station on three dates in 1974 are compared. Distributions were generally comparable between the stations for both years. Total zooplankton density did not show large year to year variation, but composition of the major taxa differed between years. Two periods of zooplankton abundance were observed 'during both years. Density in spring was low but soon Walter G. Duffy increased to a June maximum. A second period of abundance was recorded in August of 1973 and July of 1974. Den- sities in both years were low in September and showed slight increases in late fall. Total zooplankton were found concentrated at different strata during different seasons. Certain species exibited preferences for different strata of the water column. THE NEARSHORE ZOOPLANKTON OF LAKE MICHIGAN ADJACENT TO THE LUDINGTON PUMPED-STORAGE RESERVOIR BY walter G. Duffy A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Fisheries and Wildlife 1975 ACKNOWLEDGMENTS I would like to acknowledge Michigan State Univer- sity, Department of Fisheries and Wildlife, for providing this research opportunity and Consumers Power Company of Michigan for funding the study. K I wish to thank Dr. P. I. Tack, Dr. W. Conley, and Dr. T. W. Porter for their helpful suggestions. I appreciate the efforts of Dr. C. R. Liston, project manager, whose help and direction will be rememr bered. Special thanks are in order to Dr. J. E. Gannon and Kathy Bricker who helped in early taxonomic work. Dr. J. E. Gannon also reviewed the manuscript. Joan Duffy's laboratory work was most helpful. The skill of our captains, Leo Yeck and the late Russel Moran, facilitated a safe collecting program. The study would not have been possible without lthe graduate student staff at Ludington. The tireless efforts and comradeship of John Armstrong, Larry Green, John Gulvas, Fredrick Hauer, Dan Lawson, David Lechel, Greg Olson, Fred Serchuk, and Mark Simons. I would also like to thank Constance Duffy whose underStanding and help I appreciated. ii TABLE OF CONTENTS ACKNOWLEDGMENTS . . . . LIST OF TABLES . . . . LIST OF FIGURES . . . . INTRODUCTION . . . . . A REVIEW OF LAKE MICHIGAN ZOOPLANKTON STUDIES . . DESCRIPTION OF SAMPLING AREA . . . . . . . Water temperature METHODS AND MATERIALS . Field methods . . Laboratory methods Statistical methods RESULTS 0 O O O O O O 0 Total zooplankton, Total zooplankton, Composition of the Seasonal abundance zooplankton species 1973 . . . . . . . 1974 . . 1973 and 1974 zooplankton and distribution of I 1974 o o o o o 0 Vertical distribution . . . . . . . . DISCUSSION . . . . . . Horizontal distribu Variation of major between 1973 and 19 Species composition tion I O O O O O O zooplankton taxa 74 O O O O O O O 0 Vertical distribution . . . . . . . . S WRY O O O C O O O 0 COMMENT . . . . . . . . iii Page ii viii ll 17 17 18 19 23 23 23 30 48 63 74 74 76 79 81 83 84 LITERATURE CITED . . . APPENDIX . Major zooplankton 29 13 30 13 30 14 25 12 28 8 September, 1973 April, 1973 May, 1973 May, 1973 June, 1973 June, 1973 July, 1973 July, 1973 . August, 1973 August, 1973 taxa 24 September, 1973 31 October, Major zooplankton 10 3 June, 19 1 July, 15 May, 1974 . 1974 . 1974 . 1974 . July, 1974 . June, 1 August, 1974 20 4 September, 18 4 November, August, 1974 October, 1973 1974 1974 1974 taxa O O O O O O O O O O ‘ O O O O O O O O O O O O ‘ OOOOOOOOOOHOOOOOOOOIOO. \0 iv ooooooooooflooooooooooo .5 Page 86 93 93 93 95 95 98 101 101 104 104 107 107 110 110 112 112 117 119 119 123 123 127 130 130 10. 11. LIST OF TABLES Location of sampling sites, their depths and bottom sediment description . . . . . . Precision of sampling method as number of samples increases . . . . . . . . . . . . . Counts of 4 taxa of 10 replicate sub- samples 0 O O O O O O O O O O I O O O O 0 0 Size of count and accuracy obtained (from Lune, Kipling, and LeCren 1958) . . . . . . Mean numbers of zooplankton/m3 in 1973 arranged in increasing order of abundance at the sampling stations and Scheffe's interval for selected contrast . . . . . . Mean numbers of zooplankton/m3 in 1974 arranged in increasing order of abundance at the sampling stations and Scheffe's interval for selected contrast . . . . . . Species list of 1974 zooplankton . . . . . Temperatures (C°) at station 4 on three dates in 19 74 O O O O O O O I O O O O O O 0 Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 29 April 1973 . Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 13 May 1973 . . Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 13 June 1973 . . Page 10 20 20 21 26 28 49 68 94 96 97 Table Page 12. Mean abundance, coefficient of variation and percentage compositions for zooplankton collected at 6 stations on 30 May . . . . . . 99 13. Mean abundance coefficient of variation and percentage compositions for zooplankton collected at 6 stations on 30 June 1973 . . . 100 14. Mean abundance, coefficient of variations, and percentage compositions for zooplankton collected at 6 stations on 14 July 1973 . . . 102 15. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 25 July 1973 . . . 103 16. Mean abundance, coefficient of variations, and percentage compositions for zooplankton collected at 6 stations on 12 August 1973 . . 105 17. Mean abundance, coefficient of variations, and percentage compositions for zooplankton collected at 6 stations on 28 August 1973 . . 106 18. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 8 September 1973 . 108 19. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 24 September 1973. 109 20. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 4 stations on 31 October 1973 . 110 21. Mean abundance, coefficient of variations, and percentage compositions for zooplankton collected at 6 stations on 10 May 1974 . . . 113 22. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 3 June 1974 . . . 115 vi Table Page 23. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 19 June 1974 . . . 118 24. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 1 July 1974 . . . 120 25. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 15 July 1974 . . . 122 26. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 1 August 1974 . . 124 27. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 20 August 1974 . . 126 28. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 4 September 1974 . 128 29. Mean abundance, coefficient of variations, and percentage compositions for zooplankton collected at 6 stations on 18 October 1974 . 131 30. Mean abundance, coefficient of variation, and percentage compositions for zooplankton collected at 6 stations on 4 November 1974 . 133 vii Figure 1. 10. 11. 12. LIST OF FIGURES Map and location of sampling sites near the Consumers Power Pumped-Storage Reservoir Surface and bottom water temperatures at stations one, four, and six during 1973 . . Surface and bottom water temperatures at stations one, four, and six during 1974 . . Seasonal density of total zooplankton at station one in 1973 and 1974 . . . . . . . . Composition of the 1973 zooplankton at station one, (1) Cladocera, (2) nauplii, (3) Calanoida, (4) Cyclopoida, and (5) Rotifera . . . . . . . . . . . . . . . . . . Composition of the 1974 zooplankton at station one, (1) Cladocera, (2) nauplii, (3) Calanoida, (4) Cyclopoida, and (5) Rotifera . . . . . . . . . . . . . . . . . . Seasonal density of Calanoida at station one in 1973 and 1974 . . . . . . . . Seasonal density of Cyclopoida at station one in 1973 and 1974 . . . . . . . . Seasonal density of copepod nauplii at station one in 1973 and 1974 . . . . . . . . Seasonal density of Cladocera at station one in 1973 and 1974 . . . . . . . . Seasonal density of Rotifera at station one in 1973 and 1974 . . . . . . . . Seasonal density of C clo s bicuspidatus thomasi adults at stations one, four and Six in 1974 O O O O O O O O O O O O O O O O viii Page 12 14 24 31 33 35 38 41 43 46 51 Figure 13. 14. 15. 16. 17. 18. Page Seasonal density of Diaptomus sp. adults at stations one, four, and six in 1974 . . . . 55 Seasonal density of Bosmina longirostris at stations one, four, and six in 1974 . . . . 58 Vertical distribution of total zooplankton at station four on 3 June, 1 August, and 4 November, 1974 . . . . . . . . . . . . . . . 64 Vertical distribution of zooplankton at station four on 3 June, 1974 . . . . . . . . . 66 Vertical distribution of zooplankton at station four on 1 August, 1974 . . . . . . . . 70 Vertical distribution of zooplankton at station four on 4 November, 1974 . . . . . . . 72 ix INTRODUCTION The purpose of this research was to determine seasonal abundance and distribution of zooplankton in a nearshore area of Lake Michigan adjacent to a pumped storage reservoir. Zooplankton occupy a central location in aquatic food chains. Although the zooplankton are not directly utilized as a resource for man, they are the main trophic link between algae and fish. The distribution of zooplankton populations is influenced by an array of chemical, physical, and bio- logical variables. Of all the variables which affect zooplankton, temperature, food, competition, and preda- tion are believed to have the greatest impact (Brooks and Dodson 1965; Hall, Cooper, and Werner 1970). Whether these variables act independently, additively, or syner- gisticly is not clear in all cases. Great Lakes zooplankton were viewed in past years as a stable component of the aquatic ecosystem. Damman (1966) noted gradual increases in total plankton counts from Lake Michigan over a 33 year period. Studies con- ducted by Wells (1960, 1970) dispelled the idea of zooplankton stability in Lake Michigan. Wells noted dramatic changes in species composition and size of the zooplankton between 1954 and 1966. The alewife was implicated as the cause of these changes. Studies by Gannon (1972) revealed that species composition may change considerably from year to year. Studies by Roth (1973), Stewart (1974) and this study substantiate the variability of year to year zooplankton composition. A REVIEW OF LAKE MICHIGAN ZOOPLANKTON STUDIES Thirty one studies of Lake Michigan zooplankton have been undertaken to date. Lake Michigan zooplankton studies remain descriptive in nature. Earlier works concentrated on taxonomy, while later works emphasize distribution. Birge (1882) described Cladocera found in the City of Chicago water supply. Forbes (1882) described zooplank- ton Crustacea collected near Racine, Wisconsin, and Chicago, Illinois, as well as in Grand Traverse Bay. Ward (1896) included quantitative information on plankton from vertical net hauls in Grand Traverse Bay. Marsh (1895), Jennings (1896), and Kofoid (1896) described the Copepoda, Rotifera, and Protozoa respectively of Wards examination of Grand Traverse Bay. Eddy (1927) collected phytoplankton, Protozoa, Rotifera, and Crustacea using net tows nearshore in southern Lake Michigan. He obtained the first data on seasonal distribution. In the first offshore study, IAhlstrom (1936) added qualitative information on phyto— Ellankton, Protozoa, and Rotifera in southern Lake Michigan. Damman (1945) examined plankton in the City of Chicago water intake from 1926 through 1942 and again from 1943 to 1958, Damman (1960). Zooplankters were identified to genus from 1926 to 1942 and total plankton were recorded from 1943 to 1958. He conducted a similar study of plankton from the city of Milwaukee, Wisconsin water intake from 1940 through 1963 (Dammon 1966). Williams (1962, 1966) identified rotifers to genus from water intakes at Gary, Indiana, and Milwaukee, Wisconsin in 1959 through 1961 and 1961 through 1962. The first quantitative study of Lake Michigan zooplankton vertical and seasonal distribution was con- ducted by Wells (1960). He used a Clarke-Bumpus sampler to sample at a station 13 km.west of Grand Haven, Michi- gan in 1954 and another 8 km west of Frankfort, Michigan in 1955. Data on vertical distribution and seasonal abundance were obtained. Wells (1970) resampled the station 13 km west of Grand Haven in 1966 and 1968 using identical methods at the same time of year. He noted dramatic changes in species composition and size of zoo- plankton between 1954 and 1966. Most larger species had declined sharply, while those smaller species showed increases in abundance. Alewife abundance in 1966 was believed to be the causative agent. His data from 1968 gave evidence that the zooplankton were shifting back toward pre-alewife (1954) compositions after the alewife die-off of 1967. McNaught (1966) and McNaught and Hasler (1966) correlated vertical distribution and rate of movement in relation to light quality at depths for several species off Saugatuck, Michigan in 1964 and off Ludington, Michi- gan in 1965. Lane and McNaught (1970) mathematically analyzed McNaughts 1964 data and suggested that vertical migration is the major mechanism for seperating niches of omnivorous and herbivorous zooplankton in Lake Michigan. Robertson (1966) reported seasonal distribution of diaptomid copepods in western Lake Michigan for 1964. Robertson and Powers (1965, 1967) analyzed zooplankton biomass measurements made during 1964 and 1966. Ayers and Huang (1967) reported biomass measurements taken in Milwaukee Harbor during 1964. Robertson (1968) employed a Hardy continuous plankton recorder in Lake Michigan in 1965 and 1966. Swain, Olson, and Odlaug (1968, 1970) towed a continuous plankton recorder along the length of Lake Michigan in July and August of 1966 and July and October 1967. Data on horizontal distribution by genera were presented. Manny and Hall (1969) presented mid- summer zooplankton data taken near Grand Haven, Michigan in 1968. Gannon (1972) conducted the most comprehensive study of zooplankton Crustacea to date. He sampled zoo- plankton at stations in Milwaukee Harbor, 16 km east of Milwaukee, Wisconsin, and in Green Bay. Data on horizon- tal distribution of zooplankton on a transect from Mil- waukee, Wisconsin to Ludington, Michigan were also pre- sented. Seasonal distribution and abundances between these areas was compared. Alewife predation on various species was measured. Effects of eutrophication on the zooplankton community was shown via comparisons between stations. Stemberger (1974) obtained data on seasonal abundance of rotifers in Milwaukee Harbor and adjacent Lake Michigan from July 1972 through June 1973. This study added greatly to the limited data on Great Lakes Rotifera. Recently, several studies have focused on the effects of power generating facilities on the Lake Michigan zooplankton communities. Roth (1973) and Stewart (1974) studied the zooplankton in the vicinity of Cook Nuclear Plant, Bridgeman, Michigan in 1972 and 1973. This study of southeastern Lake Michigan continues at this time. Industrial Biotest Laboratories (1973) studied the effects of thermal effluents from power plants in southwest Lake Michigan. DESCRIPTION OF SAMPLING AREA The inshore sampling area of Lake Michigan was 6.4 km (4.0 mi) south of Ludington, Michigan, adjacent to the pumped-storage hydro—electric plant (Fig. 1). Station one was 4.8 km (3 mi) south of the breakwall (Table 1). Station one served as the control station because this site was considered to be unaffected by currents from the power plant. Station two was 1.6 km (1 mi) south-southeast of the southern jetty. Station three was .8 km (.5 mi) south of the breakwall. Station four was about 2.4 km (1.5 mi) west-southwest of the breakwall. Station six was 1.6 km (1 mi) north of the northern jetty. Sampling station depths and bottom sediment composition are shown in Table 1. Deposition of bottom material at stations two and three resulted in depth changes at these stations between November 1973 and April 1974. In 1974 the depth at station two was six meters and at station three twelve meters. Figure 1.--Map and location of sampling sites near the Consumers Power Pumped-Storage Reservoir. //////// LUDINGTON/ Pore Alarquoffo Lat: v‘. c k... 0.0.0.50...” .:...0. 000-0000. gsgzézée: R E SERVO'R 00.. IIIIIIIII O on I ........................... ......................... oooooooooooooooo .............. ....................... OOOOOOOOOOOOOOOO OOOOOOOOOOOOOOO ............................. ............................ ........................ IIIIIIIIIIIII ......................... OOOOOO .......................... ......................... IIIIIIIIIIII ..................... OOOOOOOO IO. ..... .:.:. IO. ..... O. 0" .0 ........ ttttt .00.... ...... '''''''''''''' ooooooooo '''''''''''''''''' ..... SAMPLING STATIONS I Ludington Pumped Storage Project N 1:1 | :1! miss 3 ‘1' ‘7’ 1"IIP Jili'lf'4:r ‘4"'1‘7'¢3'17' uuuuu -4 Bass Lake .8 NH mmusu sowumum us was E m mm3 ozu soaumum um swamp map ehma CH .1. 10 mxoon .ocmm m =OH .em 0mm gem .vm‘ ems o mxoou .He>mum .ocmm NH =mm .em com =o~ .«m ems m ussm mesmao new ccmm spasm «N =oo .mm 0mm =om .mm one s Hm>mum .ocMm «4H =o~ .em 0mm =m .mm one m mama «m =om .mm 0mm =me .Nm ome m scum NH =o~ .em 0mm =oo .Hm omw a mmhe AEV numwo .msoq 3 .DMA z sowumum .sowumwuommo usmswomm Eouuon can mnumwp menu .mmuwm mcflamfimm mo coaumooqII.H.mnm¢B 11 Water Temperature Water temperature measurements taken at stations of three different depths are shown in Figures 2 and 3. Unstable thermal conditions existed during both years due to vertical movements of the thermocline, station four in 1974 being an exception. These "upwellings" are common along the eastern shore and have been documented by vari- our authors (Carr, Moffett, and Gannon 1973; Liston et. a1. 1974; and Siebel and Ayers 1974). Upwellings during both years are indicated by temperature drops during June through Septemeber in Figures 2 and 3. Siebel and Ayers (1974) said, "Direct wind influenced upwelling is thought responsible for the natural daily fluctuations in excess of 12°F while a combination of factors seems a palusible explanation for the smaller ranges." The greatest upwelling occurred on 22 August, 1973. At the shallow zones, temperatures dropped from 22°C on 15 August, to 5°C on 22 August. On 27 August water tempera- tures were 20°C again. Another strong upwelling occurred on 17 September 1973. Examination of Figure 3 illustrates that 1974 water temperatures could be characterized as being more stable in the June to September period. At the deepest station (four) a thermocline developed in June which persisted through September. 12 Figure 2.--Surface and bottom water temperatures at stations one, four, and six during 1973. 13 ”amoeba: mums—whmwm_ kwbwad _ >43... mzzw >42 Izmdd I v A 52.8 A. ,1. \ x.\\ I mop—Em .1 II I 8.9.0 2925 18 L _ _ _ l _ \ \ I I '|'| 1"II \IIIIIIII.\ I \ I/ \\; \\ l o. 00 . II--- Eotom \ .1. III 88.5 III. new. .1» 29.5.5 Low \ . fi‘- I —-"-- -- ------‘ ----- c. In. .’ '-‘ —-'- ‘ -’— 0 \\\\II/ N”! \\\Il \ ‘11 ’\\\ I. m x / . / \ z .. ,. .. x ., t . o. \I .1 .. n .3, . \\ Oo ’ I‘I“ IIIII ,, l l I / .1 2 I seem .2 / . n \ x e. \ I \\ /. u Is <. .. \x I III Oothamw \\\ c " III a New. ._ 29.5.5 Low. 14 Figure 3.--Surface and bottom water temperatures at stations one, four, and six during 1974. 15 CmmOkOO mwmzwkmmm 5.94034 >43... MZDfi >42 I:E< F e _ _ L _ _ o I a IIIIIIIIIIIIIIII I o. ..... seam I III coon—Sm o. I om _ L _ _ c _ _ o I n I o. I 2 III 835m ..... Eozom III 88.5 Lib. ._ zo_._.<._.m l gum. 3» 22.2.5 I ON 0. n. ON Do Do 16 A general year by year comparison reveals that water temperatures were slightly greater in April, 1973, and attained higher maximum values (23.0°C in 1973; 21.0°C in 1974). Natural variations in warm-up time, maximum temperatures, and temperature stability existed between years. These year by year fluctuations no doubt influence primary and secondary productivity in the lake. METHODS AND MATERIALS Field Methods Zooplankton samples were taken between 7:00 A.M. and noon biweekly from 29 April through 31 October, 1973 and 10 May through 4 November, 1974 using a pump and net method (Edmondson and Winberg, 1971). Adverse weather sometimes dictated changes in the sampling schedule. Duplicate samples were taken at depths of one meter, four meters, and one meter above bottom at each station. At stations two and six in 1974, only one and four meter collections were taken. The collection technique was as follows: (1) 100 liters of water was pumped through a number 20 mesh (64u) nylon plankton net; (2) the samples were emptied into sample bottles and preserved in 10% formalin; (3) the preserved samples were allowed to settle at least one week and were then aspirated down; (4) the 10% formalin was replaced with 70% ethanol and several drops of glycerol. After the concentration process samples were approximately 50ml in size. In 1974 several ounces 17 18 of club soda were added to each sample prior to preser- vation in formalin to relax the animals and minimize distortion of taxonimic features, (Gannon and Gannon, 1975). Laboratorprethods The 1973 samples were enumerated to major groups only; i.e., copepod nauplii, Calanoida, Cyclopoida, Cladocera, and Rotifera using a counting wheel (Ward, 1955) and binocular microscope (magnification 7-60x). Each sample was mixed using a magnetic stirrer with care taken not to stir the sample faster than necessary. After the sample had mixed a sub-sample of 5 to 10ml was removed from the center of the sample using a 50ml syringe, and the organisms were enumerated. The 1974 samples were identified to species using a binocular microscope (magnification 10-280x), a compound micrOSCOpe (magnification 100-400x), and a chambered counting cell (Gannon, 1971). Each sample was drawn off. ‘Sub-sample size was gauged so as to count 100-150 of the common species. When zooplankton were abundant and the sub-sample was small, a second sub- sample of 10ml was taken and only uncommon species were enumerated. Taxonomy follows Brooks (1959), Chengalath et. a1. (1971) Deevey and Deevey (1971), Pennak (1963), and Wilson (1959). 19 Statistical Methods Estimation of zooplankton populations in the lake depend on the precision of the sampling method, random distribution of assume subsamples enumerated in the lab- oratory and errors of enumeration are random. Mosely (1974) suggests that the effect of continued sampling on precision of observations can be measured by the formula D = s/ n i. Where D = units of precision, s = the standard deviation, n = number of samples, and the mean number of organisms in n samples. He says i that increasing the value of n (samples) will illustrate the effect of continued sampling on precision, assuming a good estimate of the standard deviation(s) is available. This formula was applied to total zooplankton data collected on 3 June 1974. The test was applied in increments of sampling stations to determine the precision gained as the number of stations increased. Results imply that precision gained after 22 samples (4 stations) is slight (Table 2). Because of the labor involved in collecting and counting samples a reduction in total samples is justified. This could also free the investi- gator of excess labor and allow a more detailed analysis of the data. A test for randomness of subsamples and counting errors was performed by removing 10 replicate 2 m1 sub- samples from one 50 m1 sample. Bosmina sp., nauplii, 20 TABLE 2.-—Precision of sampling method as number of samples increases, where D = s/ n x. Number of samples 6 12 16 22 26 32 D 0.45 0.30 0.26 0.22 0.20 0.18 Cyclops sp., and Diaptomus sp. were counted using proce- dures identical to thos employed in 1974. Each subsample was returned to the sample bottle following enumeration. The Chi-square (x2) was used to test for randomness of these data (Lune, Kipling, and LeCren, 1958). The four taxa enumerated satisfied the condition of randomness (Table 3). TABLE 3.--Counts of 4 taxa of 10 replicate subsamples. Organism Bosmina Cyclops Diaptomus Nauplii l 62 39 28 9O 2 59 34 29 77 3 42 43 22 89 4 61 43 27 93 5 45 39 14 103 6 51 28 31 91 7 50 33 16 70 8 49 44 16 96 9 44 45 19 103 10 50 42 25 101 Mean i(95%) 51.3:5.0 39.0:3.8 22.7:3.9 91.3:7.9 x2 8.8 7.2 - 11.9 12.5 Data exhibit randomness if X2 < 16.92. 21 When randomness of subsampling and counting procedures is satisfied, accuracy of counts can be estimated from confidence limits based on the Poisson distribution. An examination of Table 4 shows that accuracy is very low when counts are low (Table 4). It is clear from Table 4 that a compromise between accuracy of counts and labor spent obtaining accuracy must be made. TABLE 4.--Size of count and accuracy obtained. Number of organisms Expressed as percentage counted of count Range 4 i 100% 0-8 16 i 50% 8-24 100 i 20% 80-120 400 i 10% 360-440 1,600 i 5% 1,520-1,680 10,000 i 2% 9,800-10,200 40,000 i 1% 39,600-40,400 SOURCE: Lund, Kipling, and LeCren, 1958. 22 Permanant sampling stations are established so that differences between these sites may be measured; One of the problems encountered by zooplankton workers is a large coefficient of variation between replicate samples at stations (Roth, 1973). This has the effect of destroying tests between stations. Variances can be reduced by logarighmic transformations (Elliot, 1972, UNESCO, 1968). These transformed data can then be treated with statistical methods designed for normally distributed populations. After transformation, data from the Ludington area did not satisfy the assumptions for analysis of variance; i.e., variances remained heterogeneous on all dates (Sokal and Rohlf, 1969). Because of this, these data were treated by Scheffe's interval for selected contrast. Scheffe's interval is a pair-wise comparison of means and was chosen because it can be modified to get approximate answers when variances are heterogeneous (Gill, 1972). This test is relatively insensitive to type I errors. RESULTS Total Zooplankton, 1973 Total zooplankton densities were low (7,000 - 30,000/m3) when sampling began on 29 April. Densities increased steadily through May and June (Fig. 2). Maxi- mum density observed at any station (316,000/m3) occured on 13 June, however the mean density for all stations was 134,000/m3 (Table 5). The maximum zooplankton density for all stations combined (mean density 181,000/ m3) occurred on 30 June. Zooplankton abundance (8,000 - 53,000/m3) declined sharply in July, this decline was followed by an increase in abundance (15,000 - 76,000/m3) on 12 August. Densities in September were less than 10,000/m3 at all stations, a slight increase (10,000 - 17,000/m3) was found in October. Total Zooplankton, 1974 The same general pattern of abundance noted in 1973 was found in 1974. The period of maximum abundance again was June. Densities recorded on 19 June ranged from 149,000/m3 to 247,000/m3 (Table 6). By 1 July zoo- plankton abundance (21,000 - 37,000/m3) had declined 23 24 Figure 4.--Seasonal density of total zooplankton at station one in 1973 and 1974. 25 J\ \V Ton. .. QNN 1 O F) I I) s I) T I) V’ I Qua l O 0 u 08m rah A fl on. I 2.. DON j r nNN gwxsomvsnoul Figure 24 4.--Seasona1 density of total zooplankton at station one in 1973 and 1974. ._.__ __-_.—_..—_ __————— 25 A\ \V Ion. QNN I O n I I) s '0 j I) c I 9N0 I O CO I nub W 9. k 1 on. I at I CON r DNN eve/souvsnonl 26 TABLE 5.--Mean number of zooplankton/m3 in 1973 ranked by increasing order of abundance at the sam- pling stations. line are not statistically different (P < 05). Means underscored by a common 29 April 1973 Station Mean Scheffe's 13 May 1973 Station Mean Scheffe's 30 May 1973 Station Mean Scheffe's 13 June 1973 Station Mean Scheffe's 30 June 1973 Station Mean Scheffe's 14 July 1973 Station Mean Scheffe's 25 July 1973 Station Mean Scheffe's 1 2 3 4 5 6 6989 10446 13737 17128 21120 30893 4 2 6 3 1 5 15812 31244 37143 41438 45480 46344 2 1 3 5 4 6 32864 39852 53291 54436 59381 82414 2 1 4 3 6 5 21096 60615 87562 139738 180397 316234 4 1 3 2 5 6 122695 157539 181387 203329 211849 215214 6 5 3 4 1 2 21538 23754 30710 34889 47671 60216 6 l 2 5 3 4 8675 11329 17851 19123 25039 53874 27 TABLE 5.--Continued 12 August 1973 Station 6 5 4 2 3 1 Mean 15598 30251 33909 57510 60692 76057 Scheffe's 28 August 1973 Station 4 3 6 5 1 2 Mean 7837 8302 10745 13410 14675 15061 Scheffe's 8 September 1973 Station 4 5 2 3 6 1 Mean 3562 4958 6269 6691 7568 9294 Scheffe's 24 September 1973 Station 2 6 3 1 5 4 Mean 3458 5395 6236 6798 7990 8182 Scheffe's 31 October 1973 Station 3 1 2 4 Mean 10287 10967 13494 17271 Scheffe's 28 TABLE 6.--Mean number of zooplankton/m3 in 1974 ranked by increasing order of abundance at the same pling stations. line are not statistically different (P < .05). Means underscored by a common 10 May 1974 Station Mean Scheffe's 3 June 1974 Station Mean Scheffe's 19 June 1974 Station Mean Scheffe's 1 July 1974 Station Mean Scheffe's 15 July 1974 Station Mean Scheffe's 1 August 1974 Station Mean Scheffe's 20 August 1974 Station Mean Scheffe's 4 September 1974 Station Mean Scheffe's 1 3 4 2 5 6 18528 18740 20552 26960 30475 50026 1 2 3 6 5 4 75629 83575 102632 105129 172910 227694 2 6 5 1 3 4 149777 168990 210124 221932 224813 247083 1 6 3 2 4 5 21800 24838 25965 26574 28746 37776 6 4 5 3 1 2 46740 61603 89367 92429 96450 108536 6 2 5 4 1 3 16819 30819 32842 32969 33369 36647 2 1 6 3 5 4 19523 19739 20875 25330 27665 43064 6 3 1 5 4 2 10814 13141 14901 16733 28257 36117 29 TABLE 5.--Continued 13 October 1974 Station 4 6 2 3 5 1 Mean 13250 14632 19729 20196 20666 21392 Scheffe's 4 November 1974 Station 6 5 1 3 4 2 Mean 13543 16124 17504 19653 21110 22268 Scheffe's 30 sharply. As in 1973 a second period of increased abun- dance was noted, but occurred approximately one month earlier (15 July) than in 1973. After July zooplankton densities declined in August and remained relatively low throughout the fall. Composition of the 1973 and 1974 Zooplankton Although total zooplankton densities were similar in 1973 and 1974 considerable difference was found in some major groups between years. Composition and seasonal abundances of the zooplankton by major groups is dis— cussed below. Calanoida Calanoida comprised a minor portion of the spring and early summer zooplankton. They comprised from 1-21% (Fig. 3) of the April-June, 1973 zooplankton and 1-9% (Fig. 4) of the May-June, 1974 zooplankton. In August of both years Calanoida became important constituents of the zooplankton. They represented 12-49% of the August, .1973 zooplankton and 8-38% of the August, 1974 zooplankton. Calanoida remained prominant constituents of the fall zooplankton in both years. Numerically Calanoida were more abundant in 1973 than 1974 (Fig. 5). Maximum abun- dance occurred (37,000/m3 in 1973 and 16,000/m3 in 1974) in August of both years. 31 Figure55.--Composition of the 1973 zooplankton at station one (1) Cladocera, (2) nauplii, (3) Calanoida (4) Cyclopoida, and (5) Rotifera. 00®nv ““63 .%Q 33 Figure 6.--Composition of the 1974 zooplankton at station one, (1) Cladocera, (2) nauplii, (3) Calanoida, (4) Cyclopoida, and (5) Rotifera. I. 34/ m‘fl‘m vm _ .Ameewmwmwim 35 Figure 7.--Seasonal density of Calanoida at staion one in 1973 and 1974. 36 J l973 l I I I I Is - In N N EW/SCINVSDOHI 39'} 33" '2‘ 9 6 3 37 Cyclopoida In April and May of both years Cyclopoida com- prised from 1% to 13% of the zooplankton (Fig. 3 and 4). In June, the period of maximum density, they comprised 2-26% of the zooplankton. Through July and August Cyclopoida generally comprised 3-14% of the zooplankton although exceptions to this existed. Cyclopoida became prominant members of the zooplankton in September through completion of sampling in both years. In October, 1973 they clearly predominated the zooplankton, comprising 43-50% of the total. In October and November, 1974 they represented 21-31% and 13-34% of the total zooplankton respectively. Although the percentage of the total zooplankton Cyclopoida represented was comparable between years numerical abundance was not. Maximum Cyclopoida densi- ties in 1973 (15,000/m3) were about one fourth those recorded in 1974 (56,000/m3). Differences in densities were less pronounced after the June maximum abundance period (Fig. 8). Copepod nauplii The spring zooplankton was predominated by copepod nauplii. Copepod nauplii comprised 50-83% of the zoo- plankton in April and May, 1973 and 31-73% of the total in May, 1974 (Fig. 3 and 4). Maximum densities were 38 Figure 8.--Seasonal density of Cyclopoida at station one in 1973 and 1974. 39 I! 2 L h n b 2’ l8“ IS-I I24 I gW/SONVSHOHI T It) s r '2 «I I I0 I 0 .° O 40 found on 30 May, 1973 (21,000-47,000/m3) and 3 June, 1974 (12,000-78,000/m3). After this period copepod nauplii declined both numerically (Fig. 9) and in the percentage of the zooplankton they represented (10-30%). In the period of August and September copepod nauplii comprised a larger portion of the zooplankton (17-40% in 1973 and 11-48% in 1974). This was the result of lower densities of other groups rather than an abundance of copepod nauplii.. Copepod nauplii declined in October of both years. Cladocera In April and May of both years Cladocera were scarce and comprised less than 1% of the zooplankton at most stations. Cladocera were first recorded as abundant in mid June in both years (Figs. 3 and 4). This reflects the sudden appearance of large numbers of Bosmina longirostris which comprised over 90% of the Cladocera in June. Maximum densities (47,000-97,000/m3) of Cladocera were found on 30 June, 1973 (Fig. 10). They comprised 36-51% of the zooplankton on this date. Densities in July, 1973 were 3,000-37,000/m3 and still comprised 24- 71% of the zooplankton. After July numbers declined, but Cladocera remained an important constituent of the zooplankton. 41 Figure 9.--Seasona1 density of copepod nauplii at station one in 1973 and 1974. 42 32.5 q 30- 254 glN/SONVSOOHJ. U I I I N N 43 Figure 10.—-Seasona1 density of Cladocera at Station one in 1973 and 1974. 44 I I I I I I I I I I ¢ $330: cIIII/sclNIvsnOIIl 82 - l8“ l2- 6 45 In 1974 Cladocera densities increased sharply in June, but failed to reach 1973 levels (Fig. 10). Clado- cera comprised 8-24% of the zooplankton in June, 1974. Maximum densities (l4,000-52,000/m3) were found on 15 July, at this time Cladocera comprised 29-51% of the zoo- plankton. Cladocera comprised 10-30% of the August zoo- plankton and generally made up 2-10% of the total in fall samples. Numbers of Cladocera were lower in 1974 and the period of maximum abundance was two weeks later. Rotifera Rotifera were the most abundant component of the zooplankton, particularly in 1974. Considerable difference in the percentage of the zooplankton Rotifera represented was found between years. In 1973 Rotifera densities were variable in spring (300-14,000/m3) and comprised 7-47% (Fig. 3) of the April and May zooplankton. Maximum densities (4,000-271,000/m3) were found on 13 June (Fig. 11) and comprised 22-85% of the zooplankton. After June Rotifera represented a rela- tively minor portion of the zOOplankton (l-5%) until 28 August when they comprised 8-43% of the total. Rotifera densities declined after August to 100-300/m3 by 24 September and comprised under 5% of the zooplankton. In 1974 Rotifera were abundant when sampling began on 10 May and by 19 June maximum densities of 91,000- 46 Figure 11.--Seasona1 density of Rotifera at station one in 1973 and 1974. I) D 2.89 47 c :- \ V IIIIIIIIII n o 0 I000 n8¢9n8~~-9 gW/SONVSOOHJ. 48 161,000/m3 were recorded. Rotifera comprised 59-72% of the zooplankton (Fig. 4) on 19 June. With the exception of 4 September Rotifera comprised between 13% and 39% of the zooplankton in the July to November, 1974 period. Densities were generally 3,000-8,000/m3 over the entire period, no marked decrease was noted in the fall of 1974. Seasonal Abundance and Distribution of Zooplankton Species, 1974 A total of 26 species of zooplankton Crustacea (13 Copepoda and 13 Cladocera) and 9 genera of Rotifera were collected in 1974. In addition 3 of the Rotifera were identified to species (Table 7). Five species of cyclopoid c0pepods were collected --Cyclops bicuspidatus thomasi, Cyclops vernalis, Eucy- clops agilis, Mesocyclops edax, and Tropocyclops prasinus mexicanus. Cyclops bicuspidatus thomasi and Tropocyclops were found on all sampling dates. The most abundant copepod collected was g. bicuspidatus thomasi. Adults reached maximum densities (2,000-24,000/m3) on 3 June (Fig. 12). After June adults decreased numerically through November. However, the percentage of the zooplankton they represented was greatest in July (3-17%) and they continued to represent an important portion of the zooplankton through November. 49 TABLE ‘7.--Species list of 1974 zooplankton. Cyclopoida Cyclops bicuspidatus thomasi S. A. Forbes Cyclops vernalis Fischer Eugyclgps agilis (Koch)* Mesocyclops edax (S. A. Forbes)* Tropggyclops prasinus mexicanus Kiefer Harpacticoida Canthocamputs sp. Calanoida Diaptomus ashlandi Marsh Diaptomus minutus Lilljeborg Diaptomus oregonensis Lilljeborg Diaptomus sicilis S. A. Forbes Eurytemora affinis (Poppe) Epischura lacustris S. A. Forbes Limnocalanus macrurus Sars Cladocera Bosmina longirostris (O. F. Muller) Eubosmina coregoni (Baird) Daphnia retrocurva S. A. Forbes Daphnia galeata mendotae Birge Daphnia longiremis Sars** Daphnia schodleri Sars** " Chydorus sphaericus (O. F. Muller) Holopedium gibberum Zaddach Polyphemus pediculus (Linne) Ceriodaphnia quadrangula (O. F. Muller) Diaphonosoma leuchtenbergianum Fischer** Alona affinis (Leydig) Leptodora kindtii (Focke) 50 TABLE 7.--Continued. Rotifers Keratella cochlearis Gosse" Keratella quadrata O. F. Muller Kellicottia longispina (Kellicott) Asplanchna sp. Polyarthra sp. Branchionus sp. Trichotrta sp. Synchaeta sp. Filinia sp. Notholca sp. *Rare species. **Recorded as single individuals. 51 Figure 12.--Seasona1 density of Cyclops bicuspidatus thomasi adults at stations one, four and Six in 1974. 52 I I I IIIIIrIIrI o <- 3 gaunhmnvnu‘o glN/SCINVSHOHI 261 24‘ 22- 20- IB- 53 Immature Cyclopssp. were not identified to species. However 9. bicuspidatus thomasi comprised 99% of the adult Cyclops sp. and Cyclops vernalis was found only occasionally. Because of this it may be assumed that most Cyclops copepodids are C. bicuspidatus thomasi. Copepodids also reached maximum densities (1,000-31,000/m3) on 3 June. Copepodids were usually more abundant than adults and were found to have the same seasonal abundance trends. Cyclgps vernalis was recorded from June through September. On all occasions it was present in low (100- 300/m3) numbers. Eucyclops agilis and Mesocyclops edax were both rare, occurring as single individuals on several dates. Tr0pocyclops prasinus mexicanus was found in low densities (about 100/m3) from May through July. In August T. prasinus mexicanus was common, maxi- mum densities being over 600/m3. On 4 September only 2 individuals of T. prasinus mexicanus were found. In October and November it was again common. Harpactacoid copepods of Canthocamptus sp. were collected occasionally in low numbers, less than 60/m3. This benthic copepod was found at all depths. Four species of Diaptomus comprised the majority of the Calanoida. Immatures of the 4 diaptomids were not identified to species. Immature Diaptumus sp. were present in relatively low numbers (300-800/m3) in May. 54 After May they became common to abundant. Maximum densities (3,000-8,000/m3) were found in November. Diaptomus ashlandi was common (BOO/m3) in May samples, but densities were low through summer. In Sep— tember Q, ashlandi became common again and remained so through November. Maximum densities of Q. ashlandi (300-800/m3) were recorded in September. Diaptomus minutus became common in June and maximum densities (over 1,300/m3) were found in August. October and November were periods of lowest densities of Q. minutus. Diaptomus oregonensis was found in low numbers from May through.August. It then became common in fall. Maximum abundance of Q. sicilis (over 700/m3) occurred in November. Diaptomus sp. adults were most abundant in August (Fig. 13) and in- creased in abundance in the fall at most stations. Three other calanoid copepods were found. To- gether they usually comprised less than 1% of the zoo- plankton, none were recorded as abundant. Eurytemora affinis was not observed in May or September, on all other dates it was present in low numbers. Maximum densities (300/m3) of Eurypemora were found at one station in August. Single individuals of Epischura lacustris were found in May and September. Epischura lacustris was found occasionally in October and November, densities were less than 100/m3. Limnocalanus macrurus was found 55 Figure l3.--Seasonal density of Diaptomus sp. adults at stations one, four, and st in 1974. 56 ISI I4‘ l3“ I2“ I0“ I I I I I a: O h 0 0 gwxsaaaounH 57 in low densities (less than 100/m3) from May through October. No Limnocalanus were found in November. Thirteen species of Cladocera were collected, of these Bosmina longirostris was by far the most abundant. B. longirostris appear capable of responding quickly with the onset of summer conditions. Low numbers of B. longirostris (less than 100/m3) were found in May. By 3 June the B. longirostris population at one littoral station had reached 10,000/m3. On 15 June B. longirostris densities were over 14,000/m3 at all stations (Fig. 14), with maximum densities being over 30,000/m3. B. longiros- ppig comprised as much as 24% and 26% of the zooplankton at certain stations in July and August, though densities had declined from June. B. longirostris was present in low numbers in September samples, but common in October and November samples. Eubosmi coregoni first appeared in July samples. It then became common in samples from August through November. However, it was never abundant and maximum densities (BOO/m3) were recorded in November. Four species of Daphnia were collected, 2 were common and 2 were collected as single individuals. The most abundant Daphnia sp. collected was B. retrocurva, which appeared in June. Maximum densities (2,500/m3) were recorded in August. In September, densities remained high (1,000/m3), in October, B. retrocurva was common, 58 Figure 14.--Seasonal density of Bosmina longirostris at stations one, four, and six In 1974. 59 f I T I I I I f 1 O O I5 O I) V IO N " O glN/SCINVSOOHI I2 I II - Io - 60 but it was not observed in November samples. Daphnia galeata mendotae was first found in August samples and was common. It remained common through November, maximum densities (ZOO/m3) were found in November. Daphnia longiremis was represented by a single individual found in September and Daphnia Sch¢dleri was recorded as a single individual in October. Chydorus sphaericus was found in low numbers on all sampling dates in the Ludington area. Findings were variable through September. In October and November Chydorus E: densities were low (less than 100/m3), but it was recorded more commonly. No population maximum could be discerned. Six species of Cladocera appeared in the late summer zooplankton, most were present only in July and August. Holopedium gibberum was found in very low numr bers in July. Numerical maxima (over 600/m3) was recorded in August. After August Holopedium g. was not observed in the sample. One individual of Po1yphemus pediculus was found in 1 July samples, maximum densities (300- 800/m3) were found on 15 July. After this densities declined through August and B. pediculus was absent from fall samples. Ceriodaphnia quadrangula was found in samples from July through mid August. It was always present in low (less than 100/m3) numbers and variable in occurrence between stations. Alona affinis appeared 61 in sampble from 1 July and 4 September. On both dates it was present in very low numbers. Diaphanosoma leuchtenbergianum was recorded as a solitary individual on 15 July. Leptodora kindtii was found at three stations on 1 August. The maximum densities being 100/m3. A single individual was also found in July. Leptodora kindtii was not found on any other date. I Empahsis in this study was placed on total rotifer abundance, however quantitative information on three species which occurred consistently was recorded. In addition, quantitative information on seven other genera which appeared briefly or in low numbers was recorded. I Keratella cochlearis was the most abundant rotifer collected through.the sampling season. A single individual was recorded in May. On 3 June the seasonal maximum (56,000/m3) occurred. Keratella cochlearis remained an important numerical constituent of the zoo- plankton through November. Stemberger (personal communi- cation) suggests that abundances of B. cochlearis which I found are probably a combination of three species, comprised mostly of B. cochlearis, but also B. crassa, and B. earlinae. Keratella qgadrata was also recorded at maximum densities on 3 June (8,000/m3). After 3 June densities 62 of B. quadrata declined through the summer and were very low in the fall. Kellicotia longispina was the only rotifer collected at all stations on each date. In May B. longispina was common, maximum densities were also found 1 on 3 June (over 8,000/m3). Kellicottia longispina remained numerically important through August and was common thereafter. Polyarthra sp. was recorded in greatest numbers on 3 June (14,000/m3). It occurred through the remainder of the season in low numbers. Branchionus sp. was observed occasionally in samples from June and July, after July it was not found. Trichotria sp. first appeared in samples from 1 August. Two species were usually present, one tentatively identified as g. longicaudatus. Both Trichotria sp. were present through November and became more common in fall samples. Byncheata sp. also appeared on 1 August and was present in low numbers through November. Filinia sp. occurred in the October and November zooplankton. It was common in November samples. Notholca sp. appeared in samples 1Samples from 19 June, 15 July and 20 August were enumerated to major taxa only. Maximum total rotifer abundance occurred on 19 June, thus maximum numbers of these species are probably higher than reported here. 63 from 3 June. It was common on this date, but was not recorded after 3 June. Vertical Distribution Sampling methods allowed the examination of vertical distribution of the zooplankton. This sampling method was designed to assess the effect of plant induced turbulence on the zooplankton community. However it became apparent that (1) storm induced turbulence far exceeded that created by the plant discharge and (2) it was not possible to maintain a vessel in such turbulence. The vertical distribution of zooplankton at station four on 3 June, 1 August, and 4 November, 1974, is discussed below and presented in Figures 15 through 18. 3 June 1974 Greatest densities of zooplankton were found at the 4 meter depth, over 370,000/m3 (Fig. 15) Lowest densities were at 24 meters. Copepod nauplii, Cyclops sp. C1-C5, Cyclgps bicuspidatus, and Kellicottia longispina were all found in greatest concentrations at 4 meters. Diaptomus sp. Cl-C5 were four times as abundant at the 24 meter depth as at either 4 or 1 meters. Distribution of Diaptomus oregonensis and B. sicilis was contrary to that found by Wilson and Roff (1973). Bosmina longirostris showed a definite preference for the 64 Figure 15.--Vertical distribution of total zooplankton at station four on 3 June, 1 August, and 4 Novem- ber, 1974. r24M 124M ’IM .24M 65 r-1 IOOOO/m3 F——1 IOOOO/m3 3 June _"I I1 I August II____, 4 November 66 Figure 16.--Vertica1 distribution of zooplankton at station four on 3 June, 1974. 67 I I 0:: IIM III 1 MM .356... U 2.2.3328... 9 2.0.96 2:50.:5 2.52.2. L ZOOOO/III Mesoaooao. ._. j... 2.52.3.0 J 22.23026 2.50.2.3 0/m3 2.2.55 2.50.2.3 5.3.? 2.52.3.0 .24M L. 'IM I-—I l5000/m3 . r--I 5000/":3 at If: I. J '4M I—_I IOOO/IIIa .24M 7...... 3.3.2.2 2:02:3- 0 2.32.0.3. 2:525 m I— d £7 .0 32:0 I—‘I ZOOOO/III3 I: 93:: I? ~4M L24M no: .0 2.52.3.0 .sescz 68 upper strata (Fig. 16). Temperatures on this date indi- cated no thermocline was present (Table 8). TABLE 8.--Temperatures (C°) at station 4 on three dates in 1974. Depth (m) 3 June 1 August 4 November 1 11.7 19.0 11.9 4 11.5 18.9 11.9 8 10.7 18.8 11.9 12 10.3 13.8 11.9 16 10.0 '6.1 11.9 20 8.8 5.5 11.9 24 8.6 5.5 11.9 1 August 1974 Greatest densities of zooplankton, over 44,000/m3, were found at the 24 meter depth. Lowest densities were found at the 4 meter depth. Copepod nauplii, immature diaptomids, immature Cyclops, and Kellicottia were all found most abundant at 24 meters (Fig. 17). Eurytemora affinis, Leptodora kindtii, Limnocalanus macrurus and Diaptomus sicilis were found at 1 meter and 24 meters only. This is puzzeling due to the presence of a strong thermocline (Table 8). Diaptomus minutus, Bosmina longirostris, Daphnia retrocurva, gyclops biscuspidatus, 69 Tropocyglgps prasinus and Keratella sp. were most abun- dant at the upper strata. Chydorus sphaericus, Eubosmina coregoni, Holopedium gibberum, Polyphemus pediculus and Daphnia galeata were completely absent from 24 meter samples. 4 November 1974 Maximum zooplankton abundance was found at the 4 meter depth, over 32,000/m3. Lowest densities were found at 24 meters. Immature diaptomids, and Cyclops bicuspidatus, Diaptomus sicilis and Tropocyclops pgasinus all were most abundant at the 4 meter depth (Fig. 18). Bpischura lacustris, Eubosmina coregoni and Daphnia galeata were present only at 4 meters. Copepod nauplii and Keratella cochlearis were most abundant at 1 meter. 70 Figure 17.--Vertical distribution of zooplankton at station four on 1 August, 1974. 2.30.35 2.0.00... 2.0.0303... II .350... 2.30.3.3... 03.0.0 0.6.30 “II I . 0.05.3.5 71 I I2....30I5 2.3.03.5... 3U 2.50.3.0 m 2.2.0.5 2.50.3.0 .03....3 2.50.3.0 III III. -IM ’4M I.24M WI 2.00... 03.3304 2.30.00... 2.52.330 50.2.0... fLWfl N IOOO/ *4M 124M 53030.0... 0.5.30.3. 0.5.30 00.0035 0.00.... 0.0.... 00 E 00.5330 I 2.32.0.3. I—I Ir—fi 2500/ m HM -4M L24M . r—-I I5000/m3 .. II. our-.0 23.0.0 .9. .o 253.33 :33: 053.03.. 2300...:- 2.00.300 0.3.0.8. 72 Figure 18.--Vertica1 distribution of zooplankton at station four on 4 November, 1974. “0430.45 [I 2.5003 4.23.0303.» f 00 I .0 2.0.0.0 0.30.0000. 0.3.0.3.. esofinflu LIL H 2.0.0.0 . 0....230. 0.....00...u LU fl“ 3 7 l—'-| BOO/m3 0.5.000 - l—"I 2000/m3 2.2.5.5.. .3330 2.50.3.0 00.500000 aim—1.63 , ..__.J 5.323 n ”Illlm J 0|.IIIII..00...000. —.|.L 2.50.3.0 . 055.00 M M I4 b24M J M W 4 MM L24M .24M DISCUSSION Horizontal Distribution When all six turbines are generating the maximum water flow from the reservoir into Lake Michigan is about 75,960 cfs. One of the major concerns of this investigation was whether this massive movement of water would affect zooplankton distributions in the vicinity of the power plant. Significant differences (P < .05) were detected between stations on 6 of the 12 sampling dates in 1973. Depth of the sampling station appeared to be the major factor governing distribution of zooplankton. The two shallowest stations had lowest densities on 6 of the 12 dates and greatest densities on 5 dates. The deepest station (24 m) had least densities on 4 dates and greatest densities on 2 dates. Densities at stations of inter- mediate depth were usually between the extremes of high and low abundance. Two groups, cyclopoid copepods and rotifers, exhibited rather consistent patterns of distribution in 1973. Cyclopoids were least abundant at the stations nearest shore on 8 sampling dates. 0n 2 dates there was 74 75 little difference between stations and on 2 dates there were least abundant at deeper stations. Conversly greatest densities of rotifers were most often found at the stations nearest shore. Rotifers also exhibited a north to south stratification. From April to 14 July greatest densities of rotifers occurred north of the breakwall. From August through September greatest densities occurred south of the breakwall. Calanoid copepods and Cladocera did not exhibit striking horizon- tal distribution patterns in 1973. Significant differences (P < .05) were detected between stations on only 4 of 10 sampling dates in 1974. Again depth of the station appeared to be the major factor affecting distribution. The two nearshore stations had lowest densities of zooplankton on 6 of 10 sampling dates. These littoral stations also had highest den- sities on 4 of the 10 dates. On 3 dates the littoral station south of the breakwall had lowest densities, while the littoral station north of the breakwall had greatest densities. The deepest station again had greatest densities during the period of maximum zoo- plankton abundance. In 1974 calanoid copepods, cyclopoid copepods, and rotifers exhibited horizontal distribution similar to that of 1973. Both calanoids and cyclopoids were found in greatest densities at 12 or 24 meter stations. 76 With the exception of several dates both.groups were also least abundant at the stations nearest shore. Rotifers were most abundant at nearshore stations on half of the sampling dates. Although rotifers tended 'to be more abundant nearshore, the pattern of distri- bution was not as pronounced as in 1973. No horizontal distribution pattern was observed in either year for Cladocera. Variation of Major Zooplankton Taxa Between 1973 and 1974 Differences between abundances of the major taxa existed between years. In 1973, Cladocera and Diaptomus sp. were abundant. Rotifera and copepod nauplii were abundant to moderate. Cyclops sp. was present in moder- ate abundance. In 1974, Cladocera and Diaptomus sp. relatively less abundant. Rotifers increased in abun- dance, and Cyclops sp. increased from 1973. Nauplii remained similar to 1973 abundances. Temperature, food, and predation are probably major regulators of the zooplankton community (Slobodkin 1954, Hall, Cooper, and Warner 1970, Edmondson 1957, McLaren 1963, Norden 1968), and may partially explain these differences. The size efficiency hypothesis of Brooks and Dodson (1965) partially explains these changes. This 77 hypothesis suggests that superior competitive abilities are related to increased body size and these abilities help exclude smaller forms from the system. Where fish are present the larger forms are eliminated and the smaller forms flourish. This could explain lower calanoid densities in 1974, however if fish were the causative agent one would expect Cyclops sp. densities to also be depressed. Norden (1968) and Gannon (1972) found that both Cyclops sp. and calanoids were positively selected by alewife in Lake Michigan. Dodson (1974) recently tested the size-efficiency hypothesis and concluded that invertebrate predators may play an important role in governing species composition of the zOOplankton. Ale- wife stomachs were not analyzed, consequently actual predation rates are unknown. Frost (1974) suggests that feeding specialization may explain the observed coexistence of small and large marine c0pepods and postulates competitive superiority of smaller species at limiting food concentrations (in contradiction to the size-efficiency hypothesis). Comita and Anderson (1959) found that the mean number of eggs carried by oviporous females of Diaptomus ashlandi was significantly correlated with the chlorophyll content of the water two weeks earlier. Edmondson (1957) suggests that zooplankton grazing may crOp off phyto- plankton faster than they are able to multiply. This 78 may imply that limiting food, rather than alewife pre- dation was the causative agent in lowering calanoid abundance in 1974. Variation in water temperatures between years is most likely the major factor contributing to observed differences in abundance of zooplankton taxa. In early May of both years temperatures were 4-6°C throughout the area. By 30 May, 1973 water temperatures had risen to 7-8°C and zooplankton densities were 30,000-80,000/m3. During the same period (3 June) in 1974 water tempera- tures were 9-13°C and zooplankton densities were 80,000- 220,000/m3. After this initial warm up period 1973 water temperatures fluctuated throughout the summer. In 1974 these fluctuations were not observed. Parker and Hazelwood (1963) found that abundance of Diaptomus leptopus was negatively correlated with water temperature while Daphnia schdleri abundance was positively corre- lated with water temperature. The period of maximum zooplankton abundance occurres a short time after diatomus reach maximum abun- dance in the Ludington area (see Liston et. al. 1974 for a discussion of diatoms from the Ludington area). Whether zooplankton crop off the diatoms or the crash in diatoms is brought about by limiting nutrients has not been determined for our data. 79 Species Composition Twenty six species of zooplankton Crustacea and nine genera of rotifers were recorded in 1974. Three of the rotifers were identified to the species level. Seven species of zooplankton Crustacea and the 3 rotifer species were present on all sampling dates. Five of the 7 Crustacea were copepods with Cyclops bicuspidatus thomasi being the most abundant. Tropocyclpps prasinus mexicanus, Diaptomus minutus, Q. ashlandi and Q. oregonen- sis were also present on all dates. Two cladocera were present on all dates, Bosmina longirostris and Chydorus sphaericus. DiaptOmus sicilis was found in all months but July and Limnocalanus macrurus was found in all months except November. The spring zooplankton was predominated by c0pe- pods, with nauplii being the most prominent group. Pre- vious studies (Gannon 1972, Stewart 1974) indicate that both the offshore and inshore zooplankton is predominated by copepods in spring. Cyclops bicuspidatus thomasi and copepodids of Diaptomus sp. were also abundant. A single individual of Epischura lacustris was found in May samples. This species is normally not found until summer in Lake Michigan (Gannon 1972, Stewart 1974). The June zooplankton was predominated by rotifers, with Keratella cochlearis being most abundant. Copepod nauplii and immature and adult Cyc10ps bicuspidatus 80 thomasis were also prominant taxa in-June. The number of copepods represented was greater than in May with Cyclops vernalis, Mesocyclops edax and Eurgtemora affinis being collected. Bosmina longirostris became abundant at most stations and comprised more than 98% of the Clad- ocera. Greatest species diversity (23 species on 1 August) was found in July and August. Bosmina longiros- tris was the predominant species and Daphnia retrocurva was abundant in August. Seven other Cladocera were also collected. Copepod nauplii and copepodids, and Cyclops bicuspidatus thomasi were abundant throughout the same pling area. Diaptomus minutus was common to abundant. Limnocalanus macrurus was collected in both July and August. Several studies have concentrated on E- macrurus in the Great Lakes (Carter 1969; Gannon and Beeton 1971). These and other studies (Wells 1960, 1970; Patalas 1969, 1971, 1972; Robertson 1966; Davis 1969; Gannon 1972; Stewart 1974) have shown this species to be a cold water stenotherm. Stewart's data from southern Lake Michigan indicates £3 macrurus occurs in low numbers in nearshore waters from April through November. Keratella cochlearis was the second most abundant species in July and August behind Bosmina. Another rotifer, Kellicottia longispina was also abundant. 81 Ceriodaphnia quadrangula, Polyphemus pediculusL Hblopedium gibberum, and Leptodora kindtii present only in July and August. As in spring, copepods predominated the fall zooplankton. COpepod nauplii and copepodids of Diatomus sp. and Cyclops bicuspidatus thomasi were the most abun- dant zooplankton present. Cyclops bicuspidatus thomasi were abundant, while Diaptomus ashlandi, Q. minutus, and Q. sicilis were all common. Bosmina lingirostris remained the most abundant Cladocera species, however Eubosmina coregoni was also common to abundant. Daphnia galeata mendotae became more common than 2. retrocurva, Q. retrocurva was absent from November samples. Keratella cochlearis remained the most abundant rotifer, but densities were much less than in summer. Vertical Distribution Total zooplankton were most abundant in the upper water layers on 3 June and 4 November. Greatest densi— ties were found at 24 meters on 1 August. Diaptomus ashlandi, Q, minutus, and Q. oregonensis were found in greatest densities at 24 m on 3 June. All other species were most abundant at l or 4 m on both 3 June and 4 November. On 1 August Diaptomus ashlandi was found only at 24 m, however 2, minutus was most abundant at l m. 82 Diaptomus sicilis, Limnocalanus macrurus, and Eurytemora affinis were collected at l m and 24 m, but not at 4 m. Copepod nauplii, immatures of Diaptomus sp. and CyclOps bicuspidatus thomasi were concentrated at 24 m. All Cladocera species were most abundant at l or 4 m. The presence of Limnocalanus m. and Diaptomus sicilis at l m on 1 August when surface temperatures were 19°C was not expected. Both species are known to inhabit colder waters (wells 1960, Wilson and Roff 1973). How- ever both species were present in low numbers and water currents may have transported them to the surface. SUMMARY Nearshore zooplankton were investigated in Lake Michigan south of Ludington, Michigan in 1973 and 1974. A pump and net method was employed in collecting sam- ples. Seasonal distribution of major taxa in 1973, and 1974 was studied. Seasonal and vertical distribution of species also were studied in 1974. In spring of both years the zooplankton was pre- dominated by copepod nauplii. Cladocerans were scarce, while other taxa were common to abundant. In early summer of 1973, the fauna was predominated by rotifers, but as summer proceeded Cladocerans became dominant. In 1973, Cladocerans did not predominate the summer fauna, but were a prominent taxa from July through.August. Rotifers pre— dominated June, 1974 samples and remained abundant through the summer. Cyclopoid copepods were much more abundant in 1974 summer collections than in 1973 collections. Calanoids were less abundant in 1974 than 1973. In fall of 1973, rotifers decreased until they were a minor portion of the fauna. Cyclopoids increased throughcnn: fall of 1973 until they dominated October samples. Nauplii, calanoids, and Cladocerans remained important 83 84 constituants of the fauna. In 1974 copepods again domin- ated the fall zooplankton. However, calanoids were slightly more abundant than were cyclopoids. Rotifer densities remained high through the fall in 1974. Twenty six species of zooplankton Crustacea and nine genera of rotifers were recorded in 1974. Three rotifers were identified to species. Seven species of zooplankton Crustacea and the three rotifer species were present on all sampling dates. Cyclops bicuspidatus thomasi was present on all dates and was the most abundant crustacean zooplankter over the entire sampling period. Tropocyclops prasinus mexicanus was found on all dates and was an important member of the fall zooplankton. Three calanoid copepods were found on all dates, Diaptomus ashlandi, Q. minutus, and oregonensis. Diaptomus minutus was the most abundant calanoid collected. Two Cladocera were present on all dates, they were Bosmina longirostris and Chydorus sphaericus. Bosmina l. was a predominant summer species. Keratella cochlearis was rare in May and abundant on all other dates. Keratella quadrata was most common in summer as was Kellicottia longispina. Comment This study was designed and conducted to evaluate the possible effects a large pumped—storage reservoir 85 might have on the nearshore zooplankton communities of 'Lake Michigan. Because the results of this study may be utilized by future investigators, possibly studying similar problems, several suggestions are in order. I feel that future investigations of the nearshore zooplank- ton would benefit in taking an array of physical, chemical, and biological data to support zooplankton data. Nutrient levels in nearshore areas probably do not correspond with those of other areas in Lake Michigan. Summer storms frequently wash clay particles into the lake at Ludington. These storms probably introduce substantial amounts of nutrients into localized areas. Massive immagration and emigration of zooplankton undoubtedly occurrs between inshore and offshore areas and from one inshore area to another. Because quantita- tive information on water movements is lacking, immagra- tion and emigration cannot be determined. Data on seasonal abundance and distribution of zooplankton in the Ludington area appear to agree with other data from nearshore areas of Lake Michigan (Stewart 1974). It appears that in 1973 and 1974 the operation of the Ludington pumped-storage reservoir did not have an adverse affect on the zooplankton of the area. However the previously mentioned natural water movements may mask any effect which pumping and generating could have on the zooplankton communities. LITERATURE CITED Ahlstrom, E. H. 1936. The deep-water plankton of Lake Michigan, exclusive of the Crustacea. Trans. Amer. Microsc. Soc., 55: 286-299. Ayers, J. C. and J. C. K. Huang. 1967. Studies of Milwaukee Harbor and embayment, p. 372-394. In: Ayers, J. C. and C. C. Chandler. Studies on __ eutrophication in Lake Michigan. Univ. Michigan, Great Lakes Res. Div., Spec. Rept. No. 30, 415 p. Birge, E. A. 1882. Notes on Crustacea in Chicago water supply with remarks on the formation of the carapace. Chicago Med. J. and Exam., 1; (1881): 584-590. Brooks, J. L. 1957. The systematics of North American Daphnia. Mem. Connecticut Acad. Arts and Sci. 13, 180 p. Brooks, J. L. and S. I. Dodson. 1965. Predation, body size, and composition of plankton. Science 150: 28-35. Carr, J. F., J. W. Moffett, and J. E. Gannon. 1973. Thermal Characteristics of Lake Michigan, 1954- 55. U.S. Fish. Wildl. Serv., Fish. Bull., 62: - 143 p. Carter, J. C. H. 1969. Life cycles of Limnocalanus macrurus and Senecella calanoides and seasonal abundance and vertical distributions of various planktonic copepods in Parry Sound, Georgian Bay. J. Fish. Res. Ed. Canada, 26: 2543-2560. Chengalath, R., C. H. Fernando, and M. G. George. 1971. Planktonic Rotifera of Ontario. Univ. of Waterloo Biol. Series No. 2, 40 p. 86 Comita, Damann, 87 G. W. and G. C. Anderson. 1959. The seasonal development of a population of Diaptomus ashlandi, Marsh, and related phytoplankton cycles in Lake Washington. Limnol. Oceaogr. 4: 37-52. K. E. 1945. Plankton studies of Lake Michigan, I. Seventeen years of plankton data collected at Chicago, Illinois. Amer. Midl. Natur., 34: 769-796. . 1960. Plankton studies on Lake Michigan, II. Thirty-three years of plankton data collected at Chicago, Ill. Trans. Amer. microsc. Soc. 12: 397—404. . 1966. Plankton studies of Lake Michigan, III. Seasonal periodicity of total plankton. Proc. 9th Conf. Great Lakes Res., Univ. Michigan, Great Lakes Res. Div., Publ. No. 15: 9-17. Davis, C. C. 1969. Seasonal distribution, constitution Deevey, Dodson, Eddy, S. and abundance of zooplankton in Lake Erie. J. Fish. Res. Ed. Canada, 26: 2459-2476. E. S. and G. B. Deevey. 1971. The American species of Eubosmina Seligo (Crustacea, Clodocera). Limnol. Oceanog., 16: 201-218. S. I. 1974. Zooplankton competition and preda- tion: An experimental test of the size efficiency hypothesis. Ecology 55: 605-613. 1927. The plankton of Lake Michigan. Bull. Illinois State Div. Natur. Hist. Surv., 11(4): 203-232. Edmondson, W. T. 1957. Trophic relations of the zoo- plankton. Trans. Amer. micrsc. Soc. 16(3): 225-245. Edmondson, W. T. and G. G. Winberg (eds.) 1971. A Elliott, manual on methods for the assessment of secondary productivity in fresh waters. IBP handbook No. 17, 358 p. J. M. 1971. Some methods for the statistical analysis of samples of benthic invertebrates. Freshwater Biol. Assoc., Scientific Publ. No. 25, 144 p. 88 Forbes, S. A. 1882. On some Entomostraca of Lake Michi- gan and adjacent waters. Amer. Natur., 16: 537-542, 640-649. Frost, B. W. 1974. Feeding processes at lower trophic levels in pelagic communities. The biology of the oceanic Pacific, 33rd Annual Biology Colloq., Oregon State Univ. Gannon, J. E. 1971. Two counting cells for the enumer- ation of zooplankton micro-Crustacea. Trans. Amer. Microsc. Soc. 29(4): 486-490. . 1972. A contribution to the ecology of zoo- plankton crustacea of Lake Michigan and Green Bay. Ph.D. thesis, Univ. Wisconsin, 257 p. and A. M. Beeton. 1971. The decline of the large zooplankter Limnocalanus macrurus Sars (Calanoida: Copepoda), in Lake Erie. Proc. 14th Conf. Great Lakes Res., p. 27-38. and S. A. Gannon. 1975. Observations on the narcotization of crustacean zooplankton. Crust- aceana, In Press. Gill, J. L. 1972. Current status of multiple compari- sons of means in designed experiments. J. Dairy Sci. 56; 973—977. Hall, D. J., w. E. Cooper, and E. E. Werner. 1970. An experimental approach to the production dynamics and structure of freshwater animal communities. Limnol. Oceanogr. 15: 839—928. Hazelwood, D. H. and R. A. Parker. 1963. Population dynamics of sume freshwater zooplankton II. the effect of lag. Ecology 44 (1): 207-211. Industrial Biotest Laboratories. 1973. Evaluation of thermal effects in southwestern Lake Michigan, 1971-1972. Waukegan and Zion Generating Stations, Report to Commonwealth Edison Co., Chicago, Illinois. Jennings, H. S. 1896. Report on the Rotatoria—with description of a new species, p. 85-93. In: Ward, in the Traverse Bay region. Bull. Mich. Fish. Comm., No. 6, 99 p. 89 Johnson, D. L. 1972. Zooplankton dynamics in Indiana waters of Lake Michigan in 1970. M.S. Thesis. Ball State Univ., Muncie, Indiana, 129 p. Kofoid, C. A. 1896. A report upon the Protozoa observed in Lake Michigan and the inland lakes in the neighborhood of Charlevoix, during the summer of 1894, p. 76-84. 13: Ward, H. B., A biological examination of Lake Michigan in the Traverse Bay region. Bull. Michigan Fish. Comm., No. 6, 99 p. Lane, P. A. and D. C. McNaught. 1970. A mathematical analysis of the niches of Lake Michigan zooplank- ton. Proc. 13th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res., p. 47-57. Liston, C. R., P. I. Tack and W. G. Duffy. 1974. A study of the effects of installing and operating a large pumped storage project on the shores of Lake Michigan near Ludington, Michigan. Vol. II. Limnological studies. 196 p. Consumers Power. Lund, J. W. G., C. Kipling and E. D. LeCren. 1958. The inverted microscope method of estimating algal numbers and the statistical basis of estimations by counting. Hydrobiologia, 11: 143-170. Manny, B. A. and A. S. Hall. 1969. Diurnal changes in stratification and dissolved oxygen in the surface waters of Lake Michigan. Proc. 12th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res., p. 622-634. Marsh, C. D. 1895. On the Cyclopidae and Calanidae of Lake St. Clair, Lake Michigan, and certain of the inland lakes of Michigan. Bull. Mich. Fish. Comm., 5: 24 p. McLaren, I. A. 1963. Effects of temperature on growth of zooplankton,aand the adaptive value of vertical migration. J. Fish. Res. Ed. Canada, 10(3): 685-726. McNaught, D. C. 1966. Depth control by planktonic cladocerans in Lake Michigan. Proc. 9th Conf. Great Lakes Res., Univ. Michigan, Great Lakes Res. Div., Publ. No. 15: 98-108. Mosely, Norden, 90 S. C. 1974. Preoperational distribution of benthic macroinvertebrates in Lake Michigan near the Cook Nuclear Power Plant, p. 5-138. 13: The biological, chemical, and physical character of Lake Michigan in the vicinity of the Donald C. Cook Nuclear Plant. Seibel, E. and J. C. Ayers. 1974. Spec. Rep. No. 51, Univ. of Michigan, Great Lakes Res. Div. C. R. 1968. Morphology and food habits of the larval alewife, Alosa pseudoharengus (Wilson), in Lake Michigan. Proc. 11th Conf. Great Lakes Res., Int. Assoc. Great Lakes Res.: 103-110. Patalas, K. 1969. Composition and horizontal distri- Pennak, bution of crustacean plankton in Lake Ontario. J. Fish. Bd. Canada. 16: 2135-2164. . 1971. The comparison of crustacean plankton communities of seven North American Great Lakes. Abstracts, 14th Conf. Great Lakes Res., p. 109- 110. . 1972. Crustacean plankton and the eutrophi- cation of the St. Lawrence Great Lakes. J. Fish. Res. Ed. Canada. 11: 1451-1462. R. W. 1963. Species identification of the fresh- water cyclopoid Copepoda of the United States. Trans. Amer. Micros. Soc., 11 (4): 353-359. Robertson, A. 1966. The distribution of calanoid copepods in the Great Lakes. Proc. 9th Conf. Great Lakes Res., Univ. Michigan, Great Lakes Res. Div., Publ. No. 11: 129-139. . 1968. Abundance, distribution and biology of plankton in Lake Michigan with the addition of a research ships of opportunity project. Univ. Michigan, Great Lakes Res. Div., Publ. No. 35, 42 p. , and C. F. Powers. 1965. Particulate organic matter in Lake Michigan. Proc. 8th Conf. Great Lakes Res. Univ. Michigan, Great Lakes Res. Div., Publ. No. 11: 175-181. 91 Robertson, A. and C. F. Powers. 1967. Comparison of the distribution of organic matter in the five Great Lakes, p. 1-18. 13: Ayers, J. C. and D. C. Chandler, Studies on the eutrophication of Lake Michigan. Univ. Michigan, Great Lakes Res. Div., Spec. Rept. No. 30, 415 p. Roth, J. C. 1973. Study of zooplankton. 1p: J. C. Ayers and E. Seibel. Benton Harbor power plant limnological studies. Part XIII. Cook Plant preoperational studies 1972. Univ. Michigan, Great Lakes. Res. Div., Spec. Rep. No. 44, 281 p. Seibel, E. and J. C. Ayers. 1974. Natural lake water temperatures in the nearshore waters of south- eastern Lake Michigan. 13: Seibel, E. and J. C. Ayers. 1974. The biological, chemical, and physical character of Lake Michigan in the vicinity of the Donald C. Cook Nuclear Plant. Univ. Michigan, Great Lakes Res. Div., Spec. Rept. No. 51, 475 p. Slobodkin, L. B. 1954. Population dynamics in Daphnia obtusa Kura. Ecol. Monogr. 11: 68-88. Sokal R. R. and F. J. Rohlf. 1969. Biometry, the prin- ciples and practice of statistics in biological research. W. H. Freeman and Co. San Francisco, 776 p. Stemberger, R. S. 1974. Temporal and spatial distri- butions of rotifers in Milwaukee Harbor and adjacent Lake Michigan. Proc. 17th Conf. Great Lakes Res. Internat. Ass. Great Lakes Res. In Press. Stewart, J. A. 1974. Lake Michigan zooplankton commu- nities in the area of the Cook Nuclear Plant. In: Seibel, E. and J. C. Ayers. 1974. The Biological, chemical, and physical character of Lake Michigan in the vicinity of the Donald C. Cook Nuclear Plant. Univ. Michigan, Great Lakes Res. Div., Spec. Rep. No. 51., 475 p. Swain, W. R., T. A. Olson, and T. O. Odlaug. 1968. Preliminary studies of zooplankton distribution with the continuous plankton recorder. Univ. Minnesota, Water Resources Res. Center, Bull. No. 7, 21 p. 92 , and . 1970. The ecology of the second trophic level in Lakes Superior, Michigan and Huron. Univ. Minnesota, Water Resources Res. Center, Bull. No. 26, 151 p. United Nations Educational, Scientific and Cultural Organization. 1968. Zooplankton sampling, UNESCO Monogr. Oceanogr. Meth. No. 2, 174 p. Ward, H. B. 1896. A biological examination of Lake Michigan in the Traverse Bay region. Bull. Michigan Fish. Comm., No. 6, 99 p. Ward, J. 1955. A description of a new zooplankton counter. Quart. J. Microsc. Sci. 16: 371- 373. Wells, L. 1960. Seasonal abundance and vertical move- ments of planktonic Crustacea in Lake Michigan. U. S. Fish. Wildl. Serv., Fish. Bull., 66: 343- 369. . 1970. Effects of alewife predation on zoo— plankton populations in Lake Michigan. Limnol. Oceanogr. 16(4): 556-565. Williams, L. G. 1962. Plankton population dynamics. Nat. Water Qual. Netwk., U.S. Publ. Health Serv., Publ. No. 663, Suppl. 2, 90 p. . 1966. Dominant planktonic rotifers of major waterways of the United States. Limnol. Oceanogr., 11: 83-91. Wilson, J. B. and J. C. Roff. 1973. Seasonal vertical distributions and diurnal migration patterns of Lake Ontario crustacean zooplankton. Proc. 16th Conf. Great Lakes Res. Int. Assoc. Great Lakes Res. p. 116-131. Wilson, M. S. 1959. Calanoida. 16: H. B. Ward and G. C. Whipple, 1959. Freshrwater biology 2nd ed. W. T. Edmondson Ed., John Wiley & Sons, Inc., New York. 1248 p. APPENDIX Major Zooplankton TaxaL 1973 The primary data for 1973 are presented in tables 5 through 16, counts of major taxa. Included for each station are the mean number of organisms (individuals/m3), the coefficient of variation (i.e., the standard devia- tion expressed as a percentage of the mean) of samples at the station, and the percent composition of the fauna. 29 April 1973 (Table 9) Maximum zooplankton abundances occurred at the littoral (6 meter) station, exceeding 30,000/m3. Copepod nauplii were abundant at all stations, densities at four stations being 10,000-15,000/m3. Copepod nauplii predom- inated the zooplankton, comprising more than 50% of the fauna at all stations. Calanoid copepods were common at all except station six. Cyclopoid copepods were also common at each station but six. Cladocera were'present in very low numbers throughout the sampling area. Rotifer abundance varied greatly between stations, ranging from over 300/m3 to over 14,000/m3. Total zooplankton numbers reflected this variation. Rotifers and nauplii together comprised 98.4% of the zooplankton at station six. 93 TABLE 9.--Mean abundance, and percentage composition. 94 coefficient of variation, for zooplankton collected at 6 stations on 29 April, 1973. #/m3 cv % #/m3 cv % Station 1 Station 2 Copepod nauplii 4659 17.1 66.7 7677 5.2 73.5 Calanoid copepods 1068 20.4 15.3 881 25.8 8.4 Cyclopoid copepods 936 15.6 13.4 807 3.3 7.7 Cladocerans 9 132.2 .1 81 64.1 .8 Rotifers 317 30.6 4.5 1000 12.6 9.6 Total 6989 11.6 10446 4.2 Station 3 Station 4 Copepod nauplii 10795 9.0 78.6 12778 6.5 74.6 Calanoid copepods 697 11.8 5.1 1685 13.4 9.8 Cyclopoid copepods 794 20.0 5.8 820 18.1 4.8 Cladocerans 75 64.0 .6 20 119.3 .1 Rotifers 1375 24.1 10.0 1826 12.2 10.7 Total 13737 8.8 17128 5.5 Station 5 Station 6 Copepod nauplii 12556 11.1 59.5 15642 7.1 50.6 Calanoid copepods 1205 11.0 5.7 306 28.0 1.0 Cyclopoid copepods 1084 24.5 5.1 158 22.0 .5 Cladocerans 66 90.0 .3 26 107.3 .1 Rotifers 6209 30.3 29.4 14760 10.1 47.8 Total 21120 9.9 30893 8.0 95 13 ng 1973 (Table 10) Total zooplankton densities recorded ranged from 31,000-46,000/m3, with the exception of station four which had 15,000/m3. Copepod nauplii continued to dominate the srping zooplankton, again comprising more than 50% of the zooplankton at each station. Calanoid and cyclopoid copepods were least prevelent at the deepest (24 meter) station, but abundant elsewhere. Cladocerans remained uncommon in the samples. Rotifers were a promenent taxon, and showed less variability between stations than in April.* 30 May 1973 (Table 11) Total zooplankton densities increased from 13 May samples, however percent composition of the zooplankton was relatively unchanged. Copepod nauplii continued to be the most abundant taxon at all stations. Maximum densities of copepod nauplii for 1973 occurred at station six, over 57,000/m3. Calanoids comprised from 10-20% of the zooplankton. Cyclopoid copepods also were abun- dant at all stations. Their numbers were generally half those of calanoids. Cladocera began to appear more commonly in samples and were recorded at densities of SOO/m3 for the first time. Rotifers remained abundant at all stations. *Predominant is defined as 45% or more of the total and prominent being 15-45% of the total. 96 TABLE 10.--Mean abundance, coefficient of variation, - for zooplankton and percentage composition collected at 6 stations on 13 May, 1973. #/m3 cv % #/m3 cv % Station 1 Station 2 Copepod nauplii 31327 13.9 68.9 19863 8.1 63.6 Calanoid copepods 3064 22.4 6.7 4611 17.6 14.8 Cyclopoid copepods 1546 22.4 3.4 2576 25.0 8.2 Cladocerans 91 138.4 .2 92 111.8 .3 Rotifers 9452 25.8 20.8 4103 11.7 13.1 Total 45480 14.8 31244 7.1 Station 3 Station 4 Copepod nauplii 27327 7.6 66.0 13268 12.5 83.9 Calanoid copepods 4030 10.1 9.9 882 12.3 5.6 Cyclopoid copepods 2025 10.3 4.9 306 25.1 1.9 Cladocerans 111 94.4 .3 15 140.0 .1 Rotifers 7896 10.3 19.1 1401 9.5 8.9 Total 41438 7.1 15812 10.7 Station 5 Station 6 Copepod nauplii 25761 5.7 55.6 26095 4.2 70.3 Calanoid copepods 4084 10.0 8.8 1833 11.1 4.9 Cyclopoid copepods 2074 10.9 4.5 1177 9.6 3.2 Caldocerans 97 138.9 .2 126 86.6 .3 Rotifers 14329 4.8 30.9 7912 7.0 21.3 Total 46344 5.1 37143 4.8 97 TABLE 11.--Mean abundance, coefficient of variation, and percentage composition for zooplankton collected at 6 stations on 30 May, 1973 3 3 #/m CV % #/m CV % Station 1 Station 2 Copepod nauplii 28296 29.1' 71.0 21103 32.6 64.2 Calanoid copepods 4226 43.0 10.6 7095 53.4 21.6 Cyclopoid copepods 1411 86.1 3.5 1228 32.8 3.7 Cladocerans 220 100.4 .6 135 125.1 .4 Rotifers 5700 13.6 14.3 3295 15.7 10.0 Total 39852 24.5 32864 27.2 Station 3 Station 4 Copepod nauplii 37415 22.9 70.2 42170 10.3 71.0 Calanoid copepods 7935 26.1 14.9 7549 14.0 12.7 Cyclopoid copepods 2625 23.2 4.9 5191 24.6 8.7 Cladocerans 171 98.3 3 131 95.9 .2 Rotifers 5144 8.8 9.7 4340 7.8 7.3 Total 53291 20.3 59381 9.9 Station 5 Station 6 Copepod nauplii 33795 18.6 62.1 57578 3.4 71.7 Calanoid copepods 7088 6.3 13.0 8477 4.4 10.6 Cyclopoid copepods 4865 8.6 8.9 4263 8.7 5.3 Cladocerans 512 26.1 .9 366 19.6 .5 Rotifers 8176 11.7 15.0 11730 5.2 14.6 Total 54436 7.1 82414 3.9 98 13 June 1973 (Table 12) Maximum zooplankton densities at station five exceeded densities at station two by a factor of 15. A major shift in percentage composition of the fauna was observed on this date. Numbers of copepod nauplii declined slightly, but remained abundant. Calanoid copepods remained near 30 May abundances. Cyclopoid copepods were recorded as more abundant than calanoids for the first time. Seasonal maximum of cyclopoids was recorded at station four, over 23,000/m3. Cladocera populations increased dramatically from 30 May abundances. Cladocera were observed in densities of 8,000-22,000/m3. Rotifers dominated the zooplankton at most stations. Seasonal maximum of rotifers was recorded at station five, over 270,000/m3. However great variation of rotifer densities between stations existed. This variability was reflected in variability of total zooplankton densi- ties. 30 June 1973 (Table 13) The maximum abundance of zooplankton over all stations occurred on this date. Numbers per cubic meter were high and variation between stations moderate. Copepod nauplii and cyclopoid copepods were abundant numerically. The seasonal maximum of calanoid copepods occurred on this date. However the percentage of the TABLE 12.--Mean abundance, _ . and percentage comp031t1on 99 coefficient of variation, for zooplankton collected at 6 stations on 13 June, 1973. 3 3 #/m CV % #/m CV % Station 1 Station 2 Copepod nauplii 14880 24.6 24.6 2738 18.2 13.0 Calanoid copepods 4721 22.4 7.8 2582 19.2 12.2 Cyclopoid copepods 5991 30.2 9.9 2419 17.1 11.5 Cladocerans 8743 43.3 14.4 8664 20.8 41.1 Rotifers 26129 58.6 43.1 4694 22.5 22.2 Total 60615 27.4 21096 17.2 Station 3 Station 4 Copepod nauplii 16731 9.4 12.0 15894 25.1 18.1 Calanoid copepods 9642 8.5 6.9 7936 27.4 9.1 Cyclopoid copepods 16770 9.7 12.0 23162 41.3 26.4 Cladocerans 17535 13.5 12.5 10926 37.9 12.5 Rotifers 79060 10.8 56.6 31144 44.1 35.6 Total 139738 8.9 87562 30.5 Station 5 Station 6 Copepod nauplii 7212 5.5 2.3 10056 12.4 5.6 Calanoid copepods 7033 9.0 2.2 6106 15.1 3.4 Cyclopoid copepods 7442 8.9 2.3 8211 10.7 4.5 Cladocerans 22907 12.6 7.2 18770 17.5 10.4 Rotifers 271702 26.0 85.9 137254 16.0 76.1 Total 316234 14.7 180397 13.6 100 TABLE 13.--Mean abundance, coefficient of variation, and percentage composition for zooplankton collected at 6 stations on 30 June, 1973. 3 3 #/m CV % #/m CV % Station 1 Station 2 Copepod nauplii 7163 15.1 4.5 5169 6.9 2.5 Calanoid copepods 10612 17.0 6.7 11614 3.0 5.7 Cyclopoid copepods 8160 13.3 5.2 10727 5.3 5.3 Cladocerans 81724 13.9 51.9 97658 5.8 48.0 Rotifers 49813 35.4 31.6 78073 6.2 38.4 Total 157539 16.2 203329 4.4 Station 3 Station 4 Copepod nauplii 3919 12.1 2.2 11299 17.0 9.2 Calanoid copepods 11888 6.5 6.5 21297 13.7 17.3 Cyclopoid copepods 8218 8.8 4.5 15223 9.3 12.4 Cladocerans 90616 13.3 50.0 47648 9.8 38.7 Rotifers 66805 8.5 36.8 28165 17.1 22.9 Total 181387 5.7 122695 9.5 Station 5 Station 6 Copepod nauplii 4600 5.5 2.2 4050 19.6 1.9 Calanoid copepods 23268 14.5 11.0 13670 19.4 6.3 Cyclopoid copepods 12597 12.9 5.9 6725 14.1 . 3.1 Cladocerans 76346 20.1 36.0 94566 15.3 43.9 Rotifers 95038 21.9 44.9 96203 22.4 44.7 Total 211849 14.9 215214 17.0 101 fauna they represented was low due to Cladocera and rotifer abundances. Cladocera and rotifers were the major components of the zooplankton. The seasonal maximum of cladoerans was recorded at station two, over 97,000/m3. 14 July 1973 (Table 14) Total zooplankton numbers declined substantially from 30 June abundances. With the exception of copepod nauplii all major taxa declined in abundance from June densities. Calanoid copepods were a prominent taxon, comprising from 14 to 43% of the zooplankton. Cyclopoid copepods were recorded in densities of 1,000-3,000/m3, comprising 4.8-8.7% of the zooplankton. Cladocera remained the most abundant taxon even though their numbers were one-third to one-seventh those of 30 June numbers, their numbers ranged from 1,000-3,000/m3. 25 July 1973 (Table 15) Total zooplankton abundances reached a summer minimum on this date. This is in contrast with data by Stewart (1974) who recorded seasonal maximum of total zooplankton in southern Lake Michigan on 19 July, 1973. Densities at most stations were 10,000-20,000/m3. 102 TABLE 14.--Mean abundance, coefficient of variation, and percentage composition for zooplankton collected at 6 stations on 14 July, 1973. #/m3 cv % #/m3 cv % Station 1 Station 2 Copepod nauplii 12834 39.2 26.9 9115 13.1 15.1 Calanoid copepods 8847 43.0 18.6 8576 13.1 14.2 Cyclopoid copepods 3205 16.4 6.7 3830 9.9 6.4 Cladocerans 21054 9.2 44.2 37517 8.1 62.3 Rotifers 1731 5.9. 3.6 1178 114.6 2.0 Total 47671 13.8 60216 5.3 Station 3 Station 4 Copepod nauplii 5372 18.7 17.5 10467 18.1 30.0 Calanoid copepods 5631 17.9 18.3 9578 15.5 27.5 Cyclopoid copepods 2671 13.4 8.7 2880 18.2 8.3 Cladocerans 14461 20.8 47.1 8412 10.7 24.1 Rotifers 2575 10.3 8.4 3552 29.8 10.2 Total 30710 13.9 34889 10.4 Station 5 Station 6 Copepod nauplii 4992 32.4 21.0 5285 2.7 24.5 Calanoid copepods 4574 42.8 19.3 6361 10.9 29.5 Cyclopoid copepods 1137 79.7 4.8 1360 15.1 6.3 Cladocerans 9847 24.4 41.5 6319 5.9 29.3 Rotifers 3204 87.0 13.5 3141 6.1 14.6 Total 23754 28.2 21538 8.0 TABLE 15.--Mean abundance, 103 coefficient of variation, and percentage composition for zooplankton collected at 6 stations on 25 July, 1973. #/m3 cv % #/m3 cv % Station 1 Station 2 Copepod nauplii 1865 23.3 16.5 1682 8.5 9.4 Calanoid copepods 2032 83.3 17.9 2436 11.8 13.7 Cyclopoid copepods 815 23.0 7.2 2016 12.7 11.3 Cladocerans 5656 11.3 49.9 11256 12.4 63.1 Rotifers 667 77.7 5.9 462 26.4 2.6 Total 11329 14.6 17851 9.4 Station 3 Station 4 Copepod nauplii 1186 10.9 4.7 10529 38.9 19.5 Calanoid copepods 2761 14.6 11.0 3260 27.8 6.1 Cyclopoid copepods 2721 15.8 10.9 1899 25.7 3.5 Cladocerans 17767 9.6 71.0 37923 30.7 70.4 Rotifers 605 16.4 2.4 534 21.7 1.0 Total 25039 8.7 53874 28.2 Station 5 Station 6 Copepod nauplii 3905 10.1 20.4 1620 17.7 18.7 Calanoid copepods 6153 13.3 32.2 2186 12.7 25.2 Cyclopoid copepods 1338 10.2 7.0 429 24.4 5.0 Cladocerans 6622 14.5 34.6 3758 6.3 43.3 Rotifers 1105 15.5 5.8 683 27.0 7.9 Total 19123 10.6 8675 7.7 104 At the deepest station densities exceeded 53,000/m3 however, Calanoid copepods and copepod nauplii were prominent taxa at most stations. Calanoids were slightly more abundant than nauplii. Cyclopoid copepods were abundant at four stations, their densities being 1,300- 2,700/m3. Cladocera predominated the zooplankton at all but one station. Rotifers composed a minor portion of the zooplankton, being less than 700/m3 at most stations. 12 August 1973 (Table 16) Total zooplankton abundances ranged from over 15,000/m3 to over 76,000/m3. The percentage composition of the zooplankton again shifted from previous dates. Copepod nauplii and Cladocera were prominent taxa at all stations. Calanoid copepods were the most abundant taxon (26-49% of the fauna), but no taxon predominated the system. Cyclopoid copepods remained an important constituent of the summer fauna, their densities being 4,000-10,000/m3 at all but one littoral station. Rotifer populations increased from July densities, but variability between stations was substantial. 28 August 1973 (Table 17) After the slight increase on 12 August total zooplankton were recorded in low numbers on this date. 105 TABLE 16.--Mean abundance, coefficient of variation, and percentage composition for zooplankton collected at 6 stations on 12 August, 1973. #/m3 cv % #/m3 CV % Station 1 Station 2 Copepod nauplii 15129 8.3 19.9 14916 7.7 25.9 Calanoid copepods 37335 17.8 49.1 17055 18.2 29.7 Cyclopoid copepods 5463 11.7 7.2 4912 8.8 8.5 Cladocerans 15820 10.8 20.8 11992 10.5 20.9 Rotifers 2310 18.5 3.0 8637 43.5 15.0 Total 76057 11.4 57510 8.4 Station 3 Station 4 Copepod nauplii 19438 15.3 32.0 9888 90.7 29.2 Calanoid copepods 17546 14.6 28.9 12512 91.5 36.9 Cyclopoid copepods 10597 12.8 17.5 7305 89.7 21.5 Cladocerans 9784 16.9 16.1 3319 85.1 9.8 Rotifers 3386 9.7 5.6 886 111.7 2.6 Total 60692 11.8 33909 96.1 Station 5 Station 6 Copepod nauplii 8828 6.2 29.2 6291 14.0 40.3 Calanoid copepods 8119 8.3 26.8 4144 13.8 26.6 Cyclopoid copepods 4233 16.3 14.0 779 30.3 5.0 Cladocerans 7362 11.6 24.3 3679 11.9 23.6 Rotifers 2110 16.0 7.0 706 100.7 4.5 Total 30251 7.7 15598 11.1 106 coefficient of variation, for zooplankton TABLE 17.--Mean abundance, and percentage composition collected at 6 stations on 28 August, 1973. 3 3 #/m CV % #/m CV % Station 1 Station 2 Copepod nauplii 2673 21.0 18.2 3721 7.0 24.7 Calanoid copepods 3759 16.3 25.6 1838 11.9 12.2 Cyclopoid copepods 952 24.2 6.5 551 4.6 3.7 Cladocerans 4031 16.6 27.5 2346 10.8 3.7 Rotifers 3259 34.5 22.2 6606 11.4 43.9 Total 14675 15.5 15061 '7.2 Station 3 Station 4 Copepod nauplii 2515 7.6 30.3 1269 15.7 16.2 Calanoid copepods 1448 11.0 17.4 2906 28.2 37.1 Cyclopoid copepods 360 21.8 4.3 1145 80.6 14.6 Cladocerans 1339 12.5 16.1 1414 17.6 18.0 Rotifers 2639 9.3 31.8 1103 14.0 14.1 Total 8302 3.5 7837 14.9 Station 5 Station 6 Copepod nauplii 2754 4.7 20.5 3068 12.5 28.6 Calanoid copepods 4982 20.2 36.8 2964 11.1 27.6 Cyclopoid copepods 1361 18.0 10.2 520 14.5 4.8 Cladocerans 2509 18.8 18.7 3276 1.7 30.5 Rotifers 1805 15.0 13.5 917 101.5 8.5 Total 13410 11.6 10745 7.3 107 Total zooplankton abundances ranged from over 7,000/m3 to over 15,000/m3. No single taxon dominated the fauna on this date. Copepod nauplii were a major component, accounting for 7-30% of the zooplankton. However, calanoid copepods, cladocerans, and rotifers were the most abundant taxa. Cyclopoid copepods were the least common taxon. Cyclopoid copepods comprised less than 5% of the zooplankton at each station. 8 September 1973 (Table 18) Total zooplankton abundances recorded were 5,000-10,000/m3 with the exception of station four, where numbers were lower. Copepod nauplii, Cladocera, and rotifers all declined numerically, but remained prominent constituants of the zooplankton in percentage composition. Calanoid copepods were the most abundant taxon in samples from this date. Calanoids accounted for one-third of the zooplankton at most stations, their maximum densities were over 3,000/m3. Cyclopoid copepods remained near 28 August abundances while the percentage of the fauna they represented increased. 24 September 1973 (Table 19) Total zooplankton abundances exhibited little variation between stations. Densities of 8,000/m3 or less were recorded at all stations. Copepods together TABLE 18.--Mean abundance, 108 coefficient of variation, and percentage composition for zooplankton collected at 6 stations on 8 September, 1973. #/m3 cv % #/m3 cv % Station 1 Station 2 Copepod nauplii 2420 31.9 26.0 1757 9.9 28.0 Calanoid copepods 3029 3.3 32.6 1882 17.6 30.0 Cyclopoid copepods 1483 39.7 16.0 550 78.1 8.8 Cladocerans 1030 13.8 11.1 1011 20.6 16.1 Rotifers 1332 17.6 14.3 1070 12.5 17.1 Total 9294 15.8 6269 11.3 Station 3 Station 4 Copepod nauplii 1141 4.4 17.1 1036 14.7 29.1 Calanoid copepods 1710 22.6 25.6 1117 9.4 31.4 Cyclopoid copepods 773 21.7 11.6 491 77.6 13.8 Cladocerans 836 18.2 12.5 364 73.7 10.2 Rotifers 2231 17.1 33.3 555 15.3 15.6 Total 6691 12.0 3562 12.9 -Station 5 Station 6 Copepod nauplii 971 16.0 19.6 2067 21.8 27.3 Calanoid copepods 1940 21.7 39.1 2466 22.2 32.6 Cyclopoid copepods 554 25.6 11.2 331 93.9 4.4 Cladocerans 786 25.0 15.9 1352 18.5 17.9 Rotifers 706 9.4 14.2 1352 22.0 17.9 Total 4958 13.7 7568 19.6 109 TABLE 19--Mean abundance,. coefficient of variation, and percentage composition for zooplankton collected at 6 stations on 24 September, 1973. 3 3 #/m CV % #/m CV % Station 1 Station 2 Copepod nauplii 1859 8.9 27.4 1209 12.6 35.0 Calanoid copepods 1371 9.7 20.2 477 24.7 13.8 Cyclopoid copepods 1990 15.9 29.3 911 17.6 26.3 Cladocerans 1310 7.1 19.3 812 18.2 23.5 Rotifers 268 15.1 3.9 50 104.4 1.5 Total 6798 6.2 3458 10.8 Station 3 Station 4 Copepod nauplii 2001 6.7 32.1 1942 35.1 23.7 Calanoid copepods 1494 14.3 24.0 3024 13.9 37.0 Cyclopoid copepods 1725 15.5 27.7 1764 18.0 21.6 Cladocerans 984 29.0 15.8 687 12.5 8.4 Rotifers 32 126.1 .5 17 141.6 .2 Total 6236 10.3 8182 14.9 ' Station 5 Station 6 Copepod nauplii 1379 7.7 17.3 1907 15.3 35.3 Calanoid copepods 1707 14.9 21.4 1347 22.7 25.0 Cyclopoed copepods 1630 24.9 20.4 1247 20.1 23.1 Cladocerans 747 21.4 9.4 783 18.1 14.5 Rotifers 33 151.8 .4 113 162.9 2.1 Total 7990 19.1 5395 15.8 110 predominated the late September zooplankton. Copepod nauplii, calanoid, and cyclopoid copepods all comprised between 20% and 30% of the zooplankton at most of the stations. Cladocera were abundant at station one, but densities of less than 1,000/m3 were found elsewhere. Rotifer abundances were very low throughout the sampling area. 31 October 1973 (Table 20) High winds forced discontinuation of sampling after station four on this date. Total zooplankton abundances ranged from 10,000-17,000/m3. Copepod nauplii and calanoid copepods were abundant at all stations. Most stations exhibiting densities of 1,000-2,000/m3 for each. Cyclopoid copepods predomr inated the fauna, with maximum densities being over 7,000/m3. Cladocera were also abundant and comprised from 20% to 30% of the zooplankton. Rotifers remained at low numbers on this final sampling date of 1973. Major Zooplankton Taxa, 1974 The primary data for 1974 are presented in tables 17 through 26, counts of major taxa and species. Included for each station are the mean number of organisms (indi- viduals/m3), the coefficient of variation of samples at the station, and the percent composition of the fauna. 111 TABLE 20.--Mean abundance, and percentage composition coefficient of variation, for zooplankton collected at 4 station on 31 October, 1973. 3 3 #/m CV % #/m CV % Station 1 Station 2 Copepod nauplii 1356 8.8 12.4 1873 7.6 13.9 Calanoid copepods 1381 16.0 12.6 2496 3.9 18.5 Cyclopoid copepods 5497 9.5 50.1 6099 4.0 45.2 Cladocerans 2729 12.7 24.9 2811 3.6 20.8 Rotifers 165 13.4 1.5 216 24.2 1.6 Total 10967 5.8 13494 1.2 Station 3 Station 4 Copepod nauplii 1026 20.9 10.0 1938 11.5 11.2 Calanoid copepods 1679 21.7 16.3 1797 9.8 10.4 Cyclopoid copepods 4505 16.6 43.8 7464 10.7 43.2 Cladocerans 2719 31.1 26.4 5191 5.9 30.1 Rotifers 358 11.7 3.5 884 30.2 5.1 Total 10287 17.8 17271 6.0 112 10 May 1974 (Table 21) Total zooplankton numbers were low (18,000- 26,000/m3) at most stations. Copepod nauplii predomin- ated the sampling area with the exception of station six. Copepod nauplii abundances ranged from over 11,000/ m3 to over 16,000/m3 and comprised from 31% to 73% of the zooplankton. Calanoids were common, but their 3 at most stations. Cyclopoid densities were below 1,000/m copepods were abundant at all stations except the deepest station (four). Cyclopoid copepods comprised 3.8-12.9% of the zooplankton and their abundances exceeded 2,000/m3 at most stations. Station six, a littoral station, was predominated by rotifers and had considerably greater total zooplankton densities than other stations. Rotifers were a prominent taxon at all other stations. 3 June 1974 (Table 22) Total zooplankton densities displayed consider- able variation on this date, densities ranged from over 75,000/m3 to over 227,000/m3. Unusually large numbers of copepod nauplii (78,000/m3) and cyclopoid copepods (56,000/m3) were recorded at station four. Copepods were a prominent taxa throughout the sampling area, but their densities were generally one-fourth those of station four. Cyclopoid copepod densities showed great variation between stations. However they were abundant throughout the 113 H 0000008 00.3005... 0000000 00: 0.. m... 0000H m0 0000~ 0.0 033 .05 m . 5mm. 2. 03.088. 00383.60 9.2 m. 300008 flag 0 .Hm H MH 0.....u00Hcooo 0.300009. ~.0N 0.~H 000m H.0H MH00 0.3 0.0 000m 0.80.30”. 10¢..."me 000le H3050. 000000003 30.6% 0.5203010 50 giom. msoHngmm 00.8% H. 0.HmH 0H 0300000.. 00.83%. 55.01008 05% mHHmeHHmCOH 00.0003 H. 0.0.3 0H m.NMH 0H H. H.mmH 0H 0.300030. H. «.03 mm mimmH .H H. H.m.mH 0H mm 3.00 H. in... 0 638068.51 H. :2 0 03:80 00030.0 x000 g N. 0.00H mm H.0HH mm 0.30on0... 3500mm mmoHonmmoum. 0.3059 00030.0 0.0 N.NN mmmH 0.0 mHmm 0.~H 0.0m 83 H3 BufifimmHn g «A Ema mam m... on... m. Ema mm 8.5 mmoaowu N.HH 0.0H mon 0.0 000m 0.3 0.0m Nmmm 00303000 H. H.0HH 0m 330503 0.50033 mgm..0_.0|§0u m. 0.02 00 0. m.v0H mm 03.805 agngwfi m. 0.mHH 00 N.~MH 0H 0.H 0.00 00H H. 0.NNH mm N. 0.0NH mm 0.NHH 00 0.H ~30 Nmm 0.0m 0mm 0.~ 0.0m 00m 0.N H.0H 0H0 m.- N00 0.H «.mm 0Hm 0.0 m.0H HMHH 0.~N ~00 H.m m.mH 000 00Hoq0H0U 0&0 H.m ~00HH 0.0 0000H m.00 0.0 000NH H390... 0000000 0 IRIVI m5}. POI m5}. 0 |>bl m5\* 0.30QO m N H .80 8.330008 0000:0800 0:0 505.000.. 00 0:03ng 4.8. $02 3 so 08000.6 0 ”.0 08.838 086.8380 09.0.9590 5%.HN Hams. 114 0.0 088 m.~H 003m 0.HH «mmom HEB. 0.3 m8 ~.R SH 0.03 ca 030002 00.383me 000 SN 0000000 03000000 0300208 038.0000 ~.m omomm m.mH mvHHH m.0H 0000 0000Huom mgmwm QGOH4 H303 0000803 038300 0800.58 3000.00 304.00 3% 0.H: 00 0.8 mm 05800010. 04.80000 «all 000300 0000000 0% 00.250020 0.8 8 ~03 0N 0.HMH m Illllfilmfiflm 8H 05.2000 0.3 00 «.mm mHH 0.HmH m 0§0 00 03030.0 00303009000 92H m llmHHHm0 000% 0000 00.00% @9483 0050000 00200600009 0.02 mm o.H~H 8H 0.3.0.3.. 009000 HE msum0HmmsoHn mmHOH0& 0.0 00.3 0 0.00 mmmm 0.00 2.0 muuHu :30 m.0H OHN H.- SN 0.H: HOH 0030226 0.0 30H m m.m~ 8mm mém $0 0HfimB0H 00:08.30. deHmHm 00% o.mHH mH mHHHDHOfl: mHHHHdeOOg 0.00 8H H.0H 8H 0.03 EH mHHHon 3.8.008 0.02 HH 0.8 2. m.8H mm 0% 02:30.08 04.2 R 0.03 0... «.mHH N0 0000040; 0.03 mm m.HmH 2. 30H mm 400030; 9m 000 0.8 000 H.0H mHN 3.8033003 H0 «.2 m.m~ ~00 0.: 00m 000803838 H Hm 0. oSmH 05H 85H 0.HH 0.82 H3000: 0&008_ bul a; B. Eh 0w. 05* 0000000 0 m m m 0 m 095.3050 .000H 002 0H II.HN Hams. 115 m.~ NSSH m: msmmm m.» mmmmp HEB m.~ «.HH .83 Hum WHN mmmu ~.H 3:. mom BHmmHBoH «HHBHHHB «é de «m3 5H «.m 3: m.H H.~m $2 Hgflflflfifl «.3 m.m mafia ham 3. mmmmm 5.3 mm“: Nmmmm mHBdUBII filing oHe mé mnmmm mam Hum mmmvm «.S ma 28¢ mummflom mdnmmm 802 H.H..Hl: BE 40'»: 3 “3% BEHB 3% H. m.-H 8H MEHEEB mfimfiflu H. m.~mH OH g8 «Baa MB 383.0 mBma H.858 gonna m.~ ~.m mmmm m4. «.mH $2 m. 93. m3. gHulBIm-u ¢.~ H.OH omvm m.¢ «.mH thm h. m.mh mmw mumoocmHu mm gnaw BHBHuomfimm $.30 mmoHog gm mQOHOgQa H. Wm: mH H. EH: mm H. m.~mH OH a gmflm @3389 H. 93H .8 w. HaemH mom BB? @3on m5 H.H. 3% «.N m.mH mmmH m.H «.3 33 WE 83.3803 mmOHQHu. H.m «.m mama «in m.mm 83 o. ~.- m3 mouHo EoHoNu 3: NJ mmfiH mé 95 33 fim 3: $8. I 88838 mHHUMDUQH MHnEUmHQm H. m.RH mm H. H.3H om .ImHfi.....u...HW g H. m.HvH mm H. m.HmH m BEBE H. m.~mH mm H. m.mmH R gamma H. 9an R H. o.~mH Hm H. ~.~HH mm gamma m. 32. «mm v. 9mm mmm 1.0.332“... g H. mémH H“. H. m.HmH H.H HBmHsmm magmflo Him m.m 8mm 0.H 9mm «Hm H.H m.~m «Hm 3.6% m.m 95 H3». H.H 9% «mm m.H m.H~ vaH 8338 oéH Wm LVHSF hém ~.~H Snow fiom m.m Emma HHHBB BB8 m B ma}. w Pull me; a B. me; m N H .fimH 656 m :0 mcoflflm m um BBHHB :Buaflmoou How :0.“qu mmflfionwm can Eonmflug mo “Emu—dammwoo 60% cmmzll.mm a 116 mg: HNHmOH 92 SSE H.H Hmmnmm H62. H.H H.HH MHoH 0.H m.m 32 ms. H.H $8 qummnHmaH HHHBJIIIIHHHB H.H. H.HH ommm H.H H.HH mmHm fiH H.HH 8% Bag 33 QHH 38H m.H~ H.HH 8me H.HH H.HH mmmwm llmHHmmHfiB mHanwullmumM H.H» H.HH mmmmu H.Hm m.m OOHNOH H.5m m.~ mahHm lmHmHHuom mglIMlmw .QCOHd. 3% .3338 33% H. m.HHH ms 3% H. méHH mm goofimu «H5030 mmuoncflu 38H mmv llmll'laccmmo Ago Mllllcéfiondm H.HH H.H.H mHBH m.H ma SR m. H.H.m HSH mHHHmpHHmcoH Bamomo H.OH H.MH HHHOH H.H H.H Hmhm m. m.hm HHOH .% Bgn @3830; H. m.mHH mm BBHBBB H. H.0HH mm H. «.2: Hmm 8:8ng H. H.HHH “H H. H.HHH mom mHHBHm> mmoHon H.H H.HH Hmmm m.m o5 mHHOH 5.2 H.m~ HmmHm Haggai; Ho H.H H.HH Hmmm Hg fim $-H m.mH H.HH mmmHm mVHomqulme m.m H.HH 2mm NHH m.m OHmmm fiHm oKH Hmmmm 68883 g a H. H.HHH H.H E3 H. m ME” NH lamp: gag H. H.o~H HmH .mHHHqu g H. H.HHH mH H. H.HHH mp m.IH||m&c8muo mEBamHm H. H.HHH 2. H. H.mH mmm H. fiHH H8 3% H. 9an mm H. mde mmH Hofiflmm 3&3qu m. H.HH 5m 0.H N. 8H mmmm m.~ H.HH mmwm 3.53me m. H.HH Sm H.H H. m mfim o.m H.HH Hmmm «3938 H.HH H.H mmmmH 9mm H.HH mRHH H.HH. 93 3.2 HHHBBBHHHB w >m| ma; H B me; a Pol ms; 86am m m H .BcHucoo .HSH BE. m|.~m WEE. 117 sampling area. Calanoid copepods were abundant at all but the two littoral stations. However, calanoids com- prised a minor percentage of the fauna (see Fig. 5). Cladocera had become abundant at most stations, maximum densities of Cladocera (over 10,000/m3) were obtained from a littoral station. Rotifers dominated the fauna at all stations except four. Maximum rotifer abundances were obtained at station five, over 100,000/m3. 19 June 1974 (Table 23) Total zooplankton abundance exceeded 200,000/m3 at all but the two littoral stations. Little variation between stations was observed. Peak abundances of total zooplankton were recorded on this date. Copepod nauplii were abundant at all stations (over 6,000-25,000/m3), but did not comprise a significant percentage of the fauna. Calanoid copepods were the least abundant taxon in 19 June samples and comprised a minor percentage of the zooplankton. Cladocera were prominent at half of the stations, as were cyclopoid copepods. Rotifers dominated the zooplankton, comprising more than 59% of the fauna at all stations. At half of the stations rotifer densities obtained were over 161,000/m3. 118 TABLE123.--Mean abundance, coefficient of variation, and percentage composition for zooplankton collected at 6 stations on 19 June, 1974. #/m3 cv % #/m3 cv % Station 1 Station 2 Copepod nauplii 7743 21.3 3.5 6375 13.2 4. Calanoid copepods 8304 21.6 3.7 1011 30.7 . Cyclopoid copepods 18003 6.5 8.1 14139 19.4 9. Cladocerans 19090 12.2 8.6 36864 20.3 24. Rotifers 161860 6.3 72.9 91388 14.5 61. Total 221932 3.0 149777 13.9 Station 3 Station 4 Copepod nauplii 6837 13.4 3.0 13943 15.2 5.6 Calanoid copepods 3594 19.2 1.6 11699 34.4 4.7 Cyclopoid copepods 37268 14.0 16.6 37638 20.9 15.2 Cladocerans 26360 32.8 11.7 22708 3.9 9.2 Rotifers 161217 16.4 71.7 161093 5.2 65.2 Total 224813 14.6 247083 7.8 Station 5 Station 6 Copepod nauplii 11322 15.2 5.6 25396 2.5 15. Calanoid copepods 2553 25.7 1.2 1018 8.7 . Cyclopoid copepods 25153 10.6 12.0 15535 9.2 9. Cladocerans 30880 129.6 14.7 25977 11.9 15. 140216 145.7 66.7 101064 5.8 59. 210124 146.5 168990 5.6 119 1 July 1974 (Table 24) Total zooplankton abundances (21,000-37,000/m3) declined sharply from the previous sampling date. Copepod nauplii remained abundant at all stations and were a prominent taxon at most stations. Calanoid copepods were abundant in samples from all but the littoral sta- tions, as on previous sampling dates. Calanoids continued to comprise aminor percentage of the total composition. Cyclopoid copepods exhibited the same pattern of distri- bution as did calanoids on this date, being abundant at all but the littoral stations. Maximum cyclopoid densities recorded were over 6,000/m3. Cladocera declined in numerical abundance throughout the sampling area, but represented a larger portion of the percentage composition. Maximum cladoceran densities exceeded 9,000/m3. Rotifers dominated the fauna at all stations except four. Maximum rotifer abundances were obtained at station five over 17,000/m3. 15 July 1974 (Table 25) Total zooplankton numbers increased from 1 July abundances, maximum densities recorded at station two were over 108,000/m3. Copepod nauplii were a prominant taxon throughout the sampling area. Cyclopoid and calandoid copepods both occurred in abundance at all 120 H.Hm mmmmm H.m HSHN Wm oomHN H62. Hum mas Hon m.OH H.HH. HHmm m.~ H.HN mmm H:H.JHHmHacoH H..Hfi..8HHHmHH H. TRH mm m. mSNH HmH H. m.mHH mH SSME «3380M mHm H.om mmmm HS... Tm mmmmH m.mm H.H 88 3.80308 mHHmumumm m.mH m.om HmomH H.HH H.H mommH H.HH h.mm hNHm mumeuom H. H.HMH a find? 802. H . m .HmH m H8201 $8053 83088 aegmfiom EEQHU 85.600303 goHumfimm 0500an H. m.mHH mm H. o.HmH m 30% 000005: 30300 mgomo H. H.HmH 3 H8638 «3088 H.HH 0.8 mHmH Tm H.H momm m.mH H.H RHH .mHfiludeHmcoH random: o.mH 0.0m H.HHH m.m H.H momm o.mH H.HH HHHH _.m.HwoocmHo mm gum—509.35 MUHBHUommHmm . mHHHwa. mmoHog H. mag HH 88 modHoEomg H. m.HMH m mlHHIHmeofinm: mschmuo 83960089 H. H.HNH m mHHHFHms mmoHoHO m.~ was as H.H H.HH Hmm H.H. H.HH. «an H353 Bumsflmmsofl mmoHowu Sm 0.8 $0 H.H fimm 8m H.H H.HH HHH m0.Ho mmoHowu H.m H.HH emmH H.H H.H mHm H.m m.om HHHH moHomoHoso mHHHmHHomH 0.363% H. H.HmH m chHHHm 8% H. mamH OH 8852 9833925 mflHHOHm EMHQ H. mKHH 5H 300000080 EH0 H. «.mHH «H s. m.mH SH lmfisque ammo. H. mamH HH 8%.; m.m 9R mom H.H m.m~ mHH H.H de HSH 8.8%..le 8m «at. mam TH H.HH 8H H.H. 0.8 HHNH 88880 @5me 5.5 Em H.HH H.m 81$ mew HKm $8 HHHmHfi: 6888 w blul m5; w DUI ME; m lblU MB; 00.30% m m H How 09.330950 003% 0:0 503ng .uHo .EwHonmwoo .HSH :36 H co mcoflflm m um 68.838 cBolfiHmoou .8835... EIHN Ema. 121 H.m0H H.mMH m.mN «.mN h.mN m.mNH wmwwm mob mm mmnHH mmOMH mm momm Nmmm mH va hvm mom HH HH mam hHw mbNm =<£ O O O O O LOMN Nmmv—lo—lr-i O H mhhhm waH vs NmHmH mthH mH «mum mmmm 5N mH mNMN ommH ovmm mH mH mm Hm HHHH MMNH Hmhm mhvmm HHmH mm omhm womb NH mv mm thm oomw mm mm we Nme hmmH mHNm a OH H» mmHN Hmmm ommm Eu500uumu MHCQmmm .Mfiuoocme mummHmm MHCQQMQ Hcoowuoo MCHEomodm mHHumouHccoH MCHEmom mymooomHo mm muumammmmmmmu meOOHuommHmm 918.903 nmuu.mmmHmNmmwma. mQGMOwaE mschmum mmoH0>00QouB mHHmcum> mmoHONU mesoau mDMMUHmwsoHQ mmoHomu mouHo mmmmeu 8H80Hod mHHumSUMH musnomHmw a a msusuome mDCMHmoochdH mandudmmmmo mmammmmww mmuchEHmdeoum0Ho Hocchmm msaoymMHo mUIHU mseommeo mpHocMHmo HHHmnmc Homwmoo m0H00mw .umscHucoo .HBHH sHps Huu.H~ mnmga 122 TABLE 25.--Mean abundance: coefficient of variation, and percentage composition for zooplankton collected at 6 stations on 15 July, 1974. 3 3 #/m CV % #/m CV % Station 1 Station 2 Copepod nauplii 13502 5.3 14.0 19084 11.6 17.6 Calanoid copepods 8648 11.0 9.0 1491 10.9 1.4 Cyclopoid copepods 9882 6.9 10.2 3645 6.4 3.4 Cladocerans 31712 6.4 32.9 52096 8.5 48.0 Rotifers 32702 6.2 33.9 32220 5.1 29.7 Total 96450 4.5 108536 6.9 Station 3 Station 4 Copepod nauplii 13288 10.1 14.4 20733 12.6 33.7 Calanoid copepods 4903 14.6 5.3 7110 9.9 11.5 Cyclopoid copepods 4491 11.2 4.9 5623 20.9 9.1 5.6 0.8 Cladocerans 42113 7.8 4 18453 9.3 29.9 Rotifers 28452 8.2 3 15237 15.5 24.7 Total 92429 4.9 61603 9.3 Station 5 Station 6 Copepod nauplii 16734 9.7 18.7 9653 13.9 20.6 Calanoid copepods 5122 24.0 5.7 1731 26.7 3.7 Cyclopoid copepods 6322 18.4 7.1 2416 7.3 5.2 Cladocerans 46378 6.5 51.9 14369 15.2 30.7 Rotifers 15261 12.2 17.1 18571 15.6 39.7 Total 89367 24.1 46740 12.9 123 stations. Cyclopoid copepods being slightly more abun- dant than calanoids. Cladocerans were the most abundant taxon at most stations, comprising 29-51% of the zoo- plankton. Maximum cladoceran densities exceeded 52,000/m3. Rotifers were a prominent component of the zooplankton at all stations. Abundance of rotifers ranged from over 15,000/m3 to over 32,000/m3. 1 August 1974 (Table 26) Total zooplankton numbers exceeded 30,000/m3 at all stations except station six, where abundances were half those of other stations. Copepod nauplii comprised from 11% to 48% of the zooplankton between stations, their maximum abundance (16,000/m3) occurring at station four. Calanoid copepods were an important component of the zooplankton, comprising 7% to 12% of the zooplankton. Cyclopoid densities were generally 3,000-4,000/m3, however their maximum densities exceeded 13,000/m3. Cladocera were a prominent taxon, comprising from 10% to 33% of the fauna, their maximum abundances (10,000/m3) occurring at station two. Rotifers ranged from 5,000- 8,000/m3 between stations, comprising from 15% to 32% of the fauna. 20 August 1974 (Table 27) Total zooplankton abundance ranged from 19,000 3 27,000/m with the exception of station four where 124 11:1. N.O OHOOO N.O OHOOO 0.0 OOOOO HEB N.H O.HH ONH H.H O.N OHO O.H N.OH. OOO galHHHQ N. H.OOH OH. OH H.OH OOO H. 0.00H NH 8.000033%... 0.0H 0.0 OHOO OOH H.O OHOO O.HH 0.0 NOOO 0000208 0HH00.||0||.H0M OOH H.H OHHN 0.0N 0.0 OONO 0.0H H.O BOO 000038 a 050.2 H. O.NHH OH Hfluafl 0.08007 O. H.HOH NON N. OOH. P §l§.§H8 H. O.OO OOH N. O.HO OH. OH H.OHH HOO 3% N. 0.0NH HO H. 0.00 HNH 0.0.0038 00.0095... 0.0 H.ON OOON O.H O.ON OOHH OH H.NN OOHH 30100800040 H. O.OHH OH O. 0.00 OOH 100003.. 8.0000 0H§m00 O. TOO OOH O. H.HOH OON O. 0.0NH OOH 300000000 0.0 O.NH ONOO H.ON O.NH OOHO O.HN 0.0H 82. 3000 H 0.3.000 OOH 0.0H HOOO N.Om O.HH HONOH 0.0N 0.0 HHOO 00000008 H. H.HOH OH 00 0.300 H . O . HOH OH . 0383000000 0.300 030% H. O.HHH OH x000 0.008800% O. OOH. OHN H.H 0.0H OOH H.H 0.0H ONO 0000000: 0050000 00ng H. N.HHH HHH H. O.HOH OHH 02000982 oxw O.NH 0.0H OOHO O.H H. HH ONOH ON OOH OHON H0085 030300800 mafia H.H N.NH OOOH H.O O. HH OOO O.H N.OO OOOH O0.Ho $2on . O.mN O.HH OHOO 0.0 0.0H OHON O.HH 0.0H OOOH Homomo mflflmfluqn .mHMMQmOH m0 H. N.NHH ON 030000080940 H. H.HHH ON .8030? 80008083 O. H.OOH HHH H. O.HOH OH N. 0.00H OO 0|.IHHHI0H_..0 OHEI. Emma H. O.HHH NH N. O.HOH OH H. O.HHH ON manualo 0200.43 ON 0.0H OOO O.H O.H OOH O.H H.OH. OHO flu fie. 020. 1.00.0040. N. O.NOH OO H. O.NHH N O. 0.00 OOH 800200 0200.30 0.0 H.OH HHOO 0.0 H.HH OOON O.O H.OH NOON OYHomHIemflflm O.NH N.HH OOOH N.O HO ONON H.HH OOH NOOO 030.500 O.ON OHH KOO RNN N.OH OOOO 0.0N O.NH OHOO HHH800080000 w I>bl ME; m blol m8; w B. 8% 0300mm m N H O .HNOH .0980 H 8 08.3000 O 00 0000038 80000ng How 00.330950 003% can .SUMHE m0 003onng 0056030 0002133 Mg 125 HEB. 0.5%.?on 0.308.3me g g 03% 0000000 H. O.NHH H.H O. O.OOH OOH 0.3000 082 O.ONH OOH O. H.HOH HON O.H O.OO OOOO HH000H0 00 0.H O.ONH OO N. 0.00 OH. H.H O.HOH OOO 03030000400 H. H.OHH OH H. O.OOH OH jg 300.0008. H.OOH OHNH O.O O.OO OOOH O.N O.OH. NOO 03000000 £00006 H. O.HHH OO H. O.HHH OH 0.09% 001005.000 H. N.OO HOH 0000060 000300 $000.00 O.OO EH H. N.OO HOH 00800800200000 O.OH ONOH O.O O.O OHOH ON O.HH OOON IQJOHflO 8H 00.204 H.OH OHHO O.OH 0.0H OOOO O.OH O.NH OOOH 00000008 00 3% 0383000000 .0_HIHH0.0 8.0% H. O.HOH OO 00.00. 3% H.HN HNO O.H O.OOH OHO O.H O.HO OOO 3000. jfimfi @0303. H. O.HOH OO H. O.HHH OH 0||HH0000>.._ 002000 N.NH OOON O.HH H.OO OOOO O.N O.OH HHO 008900300033 O.O OHNH O.H.N O.OO OOHO 0.0 O.HH OOOH O0.H0.000H.0d O.OH OHOH N.OH O.ON ONNOH O.O H.NH H.OHO MmHo0om000 O.HHH ON O. H.ONH HOO N. O.OOH OO .0H0H0smj 009000000 H. O.HOH OO H. O. ONH HO 05000000 00000000000 H. O.NHH OH O. O. OH NOH 0HHH0H0 00000030 O.H O.NOH OHO [300000000 02.00003 H.ONH ONH O.H O.HOH OOO O.H O.OO OHOH 900E 02000003 O. O.ONH HON H. H.OOH HO H0500 0200030 O.O HOHH N.OH H.ON NOOO N.H. H.OH OOON O0.H0 @0de O.H HHOH O.HH H.ON OHOH O.NH ON OHOO 00H80H00 N.H NwON O.HH OHH OOOO O.OH O.OH OOHOH H3000: 0000000 .>|0I Os; O B. Os; O .6. Oak 006000 O O H 0020.380 .HOOH .0990 H|.ON H000. 126 TABLE 27.--Mean abundance, and percentage composition coefficient of variation, for zooplankton collected at 6 stations on 20 August, 1974. 3 3 #/m CV % #/m CV % Station 1 Station 2 Copepod nauplii 3687 85.6 18.7 4948 6.4 25.3 Calanoid copepods 5335 87.5 27.0 4007 9.2 20.5 Cyclopoid copepods 1116 79.2 5.6 631 3.5 3.2 Cladocerains 5655 87.7 28.6 5107 5.8 26.2 Rotifers 3932 86.0 19.9 4831 9.7 24.7 Total 19739 93.6 19523 5.8 Station 3 Station 4 Copepod nauplii 4702 10.9 18.6 12539 7.0 29.1 Calanoid copepods 4749 12.5 18.7 16584 7.3 38.5 Cyclopoid copepods 1200 10.6 4.7 2962 26.2 6.9 Cladocerains 7207 15.4 28.4 5141 13.9 11.9 Rotifers 7471 12.9 29.5 5874 ' 8.5 13.6 Total 25330 8.6 43064 7.9 Station 5 Station 6 Copepod nauplii 9033 8.1 32.6 7905 ‘6.2 37.9 Calanoid copepods 7844 21.0 28.3 5066 18.9 24.3 Cyclopoid copepods 1226 8.5 4.4 981 18.4 4.7 Cladocerains 5487 14.3 19.8 3391 7.5 16.2 Rotifers 4083 7.0 14.8 3231 20.3 15.7 Total 27665 7.2 20875 9.5 127 densities of 43,000/m3 were recorded. Calanoid copepods increased in abundance from 1 August levels and were a prominent taxon throughout the sampling area. Maximum densities (over 16,000/m3) of calanoids were recorded at the deepest station, over 16,000/m3. Cyclopoid copepods were prevelent at all but the littoral stations. However cyclopoids were a minor component of the total percent- age. Cladocera also were a prominent taxon, their 3 at all stations except six. densities exceeding 5,000/m Rotifers occurred only slightly less abundant than did cladocerans. No single taxon dominated the fauna on this date, nauplii, calanoids, Cladocera, and rotifers were all abundant. 4 September 1974 (Table 28) Maximum densities of total zooplankton were recorded at station two (over 36,000/m3) while densities at most stations were 10,000-16,000/m3. Copepod nauplii were the most abundant taxon in samples from this date, comprising more than 36% of the zooplankton at all sta- tions except six. Calanoid copepods were second in abundance to anuplii, comprising more than 20% of the fauna at all stations. Maximum calanoid densities (8,200/m3) were recorded at station two. Cyclopoid copepods also were an important constituant of the fauna, their maximum densities being over 5,000/m3. Cladocerans 128 m.0H HeHMH m.hH hHme h.o~ HomVH Agsoa m.m m.o~ mph ~.~ H.m 5mm m.H N.Hm mam mcHoMHmcoH MHquOHHme <.m w.H~ mwe m.H v.~m 5mm m. w.wm MMH mumuummw MHHMDmumx H.h m.mh mmm m.m m.mh mmNH v.m m.o~ mam mHHmchooo _MHHMDMHmM m.m~ H.mH wmom m.NH m.m omvv m.mH m.em hmmm mnmmmuom H. w.va 5H mHCHmwm MCOHm HHUUCHx muooouomq moHoochm mgemcmNHom EsumnnHm.EoHU®moHom m. ¢.mMH em H. m.m~H mm mSOHmean msuoowsu N.m ¢.o~ mmw o.m «.Hm hmOH H.m m.mh hom m>nsoonuwu MHccmwQ m. m.mmH on w. m.mm mmH m. h.Hm mm mmuoccme.mummHmo MHccddHo .h. m.mHH mm m. N.OHH mmm w. H.wm mm Hcomwuoo MCHEmonsm h.H 5.00H omm m.H m.m> vmm m. m.mw hm mHuumonHUcoH MCHemom m.o n.m~ mom N.m N.hH «NNN h.m N.ON mvm MQMOQGMHU mmummmmmmwmmwmmmw MUHOOHuommumm mHHHmm mQOHowusm xmcw mmoHomUOWMm H. N.N«H pH m.omH m mocm0meE mochmmm mQOHomoogoya H. m.mNH w mHHmch> mQOHwNU m6 «.8 m3 9m 83 «SN Tm m.mm wmfi Hing 983883 3366 m.v m.mh 5mm m.h m.NH momm v.m m.hm mva mUIHU mmmqumu m.OH m.mH mmvH m.mH H.mH Hahm m.mH m.m~ nHmN mcHomoHomU a a mg g mmmmmmma_mmmmwmmmmmww H. m.H¢H 5H m. H.NmH mOH H. m.OMH m mHHHon mgeoummwm 0.H ¢.mm hMH H.H H.mm HHe O.H o.HNH mvH mmmqummmno.mweo£QMHo m. >.mm me N.H ~.mm va msuocaa mgaoumeo >.H m.Hh «mm H.H o.mm hoe m.H h.moH Hmm HocMHnmm mseoummHo m.mH m.vH «5mm m.mH m.mH 55mm m.om H.5N whom mUIHU.mmammmmmm. m.- m.MH mmmm n.- H.m hHNm >.m~ h.m~ omom mcHocMHmo v.mm H.HH hmhw o.m¢ m.mH mHmmH m.mm O.NN mmmm HHHmsmc oommmoo w >0 2; w >0 a; w 15' 5} 386% In- m uml m H m 33 63.85% e so @393 e pm @8838 882ng How coHuHmonwnoo wmmucmoumm can 50338:, no ucwHOHmmmoo .mognm gnaw mama. 129 m.«H 38H «.mH mmSH «.mH E«m« HEB m.« H.«H mm« «.H. m.o« Be «.« Ham «on game m. «.m«H «m «. m.«mH mm m. :3 EH gflHflg O.H m6 mg «.m mam mHHH m.m «.HH omm mHHmmHsoBflflulll «.mm H.HHH 36m 93 93 Hmm« «.m «.5 «ma mILHmHflom a MGOHHH EHlellfloeowmwuH 3% .gmmwmmmmlfiswmmmOHmw H. «.meH H.H H. Ham «H flalHumllfim; m3 0&5 TH H.H.«H 2H m.« «.mmH as. o.« «.m« «B €888.th «Handed H. H.HHH mm H. «.mm ««H 68.855 38H8 «Eda H. 93H m« H. «.3 8 «. m.«MH 3 4.3832886 o.« m.«m 8« m.H O.HOH mHm H. H.OHH 8H mHHHmouHmaoH mqemom H.H mg as. «.m O.HHH 2m H.H o.m« «B 38888 mm 9350 moaooflommumm mHHHmm mHHOHomuHHw Nmmvm mQOHpmbomgq mos—83: mofimmum mmHOHomoomoum. mHIHmfiHg waHomu O.HH «.mm 83 H.H «.2: m8 H.HH m.H« Hos. Hg BuéHmmBHn 3mg m.m «:3. 3m o.m «.H« 4% 9m m.m« $3 8.8 mmonNw mSH «Hm 52 Ha m.m« m«mH m.o« H.«« «2m 8836 H. H.HHH «H mHflmsumH gfimH uddflwwu whofimfhfidm m. 33H «m H. «.«HH «H 9952 $888:qu m. m.«mH mm H. «.««H mm mHHHOHm @318me m. «43 Hm m. SSH em «. 83H Ho« mHéog H. «.«HH H.H m. «.mmH 8 m3qu 8:883 o.m «Ha an «H 92. 3« m.« H.HHH 0mm Bandung adH «H.OH omH« H.«« m.«« «.8... H.«H m.m« H9... mwuHo .IglmHo «.m« 95 Sm« «.3 H.«« mad. «.8 m.«« «m5 . n 88:38 H..«« H.« m«¢« «.2 m.mH 88 «.3 «.mH 8H3 HHHHHBE commaoo w a; « Pol a}, H. Ell 5; . mmHg m m H. .UQHHHHBHHOO JEH 398m H|.«« mama 130 declined numerically and in the percentage of the zoo- plankton they comprised. Cladocerans were recorded as abundant at only one station. Rotifers again were an important part of the fauna numerically and in percentage of the total composition. Their densities ranged from 2,000-4,000/m3. 18 October 1974 (Table 29) Total zooplankton densities exhibited little variation between stations and the total zooplankton was dominated by immature and adult copepods. Copepod nauplii, calanoid, and cycloppoid copepods comprised between 60% and 75% of the zooplankton at all stations. Maximum densities of anuplii (4,900/m3), calanoids (5,400/m3), and cyclopoids (5,600/m3) were recorded at station one. Densities of Cladocera exhibited great variability (252-l,845/m3) between stations. Rotifers comprised from 18% to 32% of the fauna and remained abundant throughout the sampling area. 4 November 1974 (Table 30) Zooplankton abundance was approximately the same as those of 18 October. Though abundant, copepod nauplii declined from October densities. Nauplii comprised from 5% to 9% of the fauna. Meximum densities of calanoid copepods (over 8,000/m3) were recorded at station three, 131 « .« ««H«« H.« ««««H H.HH «««H« .52. «.H «H« H«« «.H «H« «mm «.H «.HH. HHH «:Hmmdm. oH «HHHBHHHmvHi «. «.«HH 3 m. «.««H «m m. «.««H «« «page «#Bmumm H.H «.«H ««« «.« H.««H «H«H «.« «.HH «««H «H.H«mHfioo «$383 «.H« «.« «Hom «.«« «.«H «««« H.H« «.«H «««H «H««HHom «H538 «82 HHHHEHVH 88883 H. «.«HH «H 9308mm «afifiiom 33w «BHHommoHom H. «.«HH «H «888:8 «Boga «.H «H« «mm «.« H.«« ««H «. H.«HH HHH goofllllllmu «.Hfléldmna «. «.«« ««H «. H.««H ««H «. «.H« «HH «38cm: «83% «Hfigma «. H.«HH «« «. «H.«H ««H «. «.«HH «« 8888 «spaces «.H H.«H H«« «.« «.«« ««.HH H.H «.««H H«« «Hfi«oHH«coH H.568 «.« «.HH HHmH «.« «.«H «H«H «.« «.«« H«« 380.88 H. «.«HH «H mm «Egg H. «.«HH «H «30ng H. «.HHH «H . ««H«HHQH «moHog H. «.«HH «H «H.«« ««ng «.« H.«« «H« «.H «.«« ««« «.H H.H«H ««« «280885 «EH «H««Hm mg; mg mJOHo «.« «.HH H«HH H.« «.«« H««H «.« «.«« «H«H H««Et. «383an «mng «.«H «.« «««« «.«H «.«H «««« «.«H «.«H «««« «ouHo flmHloNu «.H« «.« «««« «.H« «.HH H««H «.«« «.«H «««« «30886 H. «.HHH «H «H.Hu.«8._«H «aHfl H. «.HHH H.H «. «.««H «m «3% Mg H. «.HHH hH mongoose gang «. «.«HH «« «. «.«« ««H «. H.««H ««H «HHHoH« «3883 «. H.H«H «H «. H.««H ««H «. «.««H H.H «38:8de «HEBamHo H. «.H«H «« «. «.«HH ««H «3|qu «Heap..llm«|H..o. «.H «.«« «H« «. «.«« H«H «.H H.«H. ««« 8529.. «3888 H.«« «.«H H«HH «.«H H.«H H««m «.«« «.«H «««H «who g «H« «.«H «««H «.H« «.« «««H H.«« «.«H ««H« «30quch H.«H «.«H «««« «.«H «.«H H««« «.«« «.«H «««H HHHmHfi..- «8&8 « B a; H. B a; H Bu .5 «£88 Iml « « m H « .HH.«H £388 «H so «53% « HE «3838 gag How 8.330950 mow-pg can .coHHEHHQV mo “EMHunmwoo 598359.. H.H—«gldm "«.ng 132 H.« ««««H ~.« ««««~ «.« ««««H «.«« H.«« «.«H ««« m. «.««H ««« [3% m. «.««H «m 1% «IHIHSWg «.«H «8 «.«H «««H «. «.«H «««H «H.H.«mHsijww «.«H «««H «.« «H«m «. H «.«« H««N ««««Huom "«ngme .962 HHunqa. «Honouafl java .mEEImNHom g a w . «NH mm mafia—«saw «300.30 «.«« ««H H.«« ««« H. «.H«H «H gig «HHEJIdma «.«HH H.«. «.«H ««H «. «.«HH «« «@334 «.H« «« «.«« ««H N. «.««H «N Hagan «.« ««« «.« ««« «. H.«HH HHH 3H3 «.« ««« «.«H «««H «.H «.~« ««~ «g «m 3ch 8H8Huo«&«m gm «quloymslm and «8H; «H« ««« m «.«H «mm «.H «.«« ««H «gang maldflllgg «.«H u««« «.« «««H «.«H «.«H «««H H«mfiflllmulHdan «.mldaoH «.« «HNN «.HH «««« «.«H «.«H «««« «VH0 «moHod «.« «««« «.« «««« «.Hm «.« ««H« «3&ng « .HmH «« «HfimsollmH Illmgflmu «HcH..«|.«« «Hg «3:82 a «.«« ««H m. «.H«H «« «Haw; H.«HH «m «.«« ««H «. «.«HH «« «H«ficommuo «EBmmHn «434.2 «1% «.H«H Hm «.«« ««H H.« «.«« H«N $5.39.. «29%3 «.«H H««« «.« «H.«H. «.«« «.«m «H«« «ouHu g «.«H «««« «.« «««« «.«« «.«~ 88 «3958 «.« «mom «.« «HHm «.«H «.«« «««« HHHmHa: «8&8 II 2; «6| «3* « «MI E; ««H«.«Mw « w m «V « .«QqflcooIdN Emma 133 N.NH ««««H N.NH ««NNN «.«H ««««H HEB. «.H «.NOH ««N «.N «.«H «H« «.H H.««H ««« «fifiHm. 8H «Huu8HHH9H N. «.««H «N «g «lduumHHB «.«H «.««N N««N «.«N «.«H «««« «.«N «.«H «««H. £52083ng «.HN «.« ««N« N.«« «.NH «««« H.«« «.«H «««« «H««Huom mgwmm. g HIiHmeHuHV . IIIImI««o«B «H 9.308% msEmnEfiom «Human? 55%ng H. N.N«H «H H. «.««H «N «««H««««m« «B830 g8 MEQMD «. «.«« ««H «. «.«NH «2 «. «.«« ««H .||||««uo«c«a ««««Hmc «2&3 «.H N.H« ««N «.« «.HN ««« «.H «.NOH ««N g8 «:Hfifioafi N.NH «.«H N««N «.« «.NH N««H «.« n«««H ««« «HHH«8H«8H «588 «.«H «.«H «««N «.NH H.«H «««N H.« «.«N «««H m« «u«oo««Ho «3% «Boeing H. «.««H «H ._.«HH_..Hm.. « 3 ”Q8 mmoag O.H «.«« ««N H1 H.HNH «« H.H «.«« ««H «.«««onm: «««H««Mm «#22685 mag «inflaomo «.« «.«N ««« H.H. «.H«H ««« «.« «.Hm H«HH g mflfimmsofi «moHQG H.«H H.HN H««N H.« «.HH «N«N «.«H N.«H «N«N «9533'on H.«H «.«H ««H« «.«H «.«H «H«« «.HN «.«H «««« ««HomoHomu N. «.«NH «« H. «.«« H«H «HHH«B«H «56$on H. «.H«H «H «H«HEW £99.95 gum: mHEMHMOOEHA «.« «.«N N«« «. «.N«H ««H «.H «.H«H H«N «HHHoH« «««««««Ho H.H «.««H «HN «. «.«« ««H w. «.««H «« H«Hgacommuo «.HéofimHo N. «.««H H« H. «.H«H «N «. N.««H «H. «3qu «gfiumflo «. «.««H «« m. «.««H «« «. «.«« ««H H«HBHfi« «23%3 «.«« «.«H «««« «.«N «.«H «««« «.«N «.«H N««« «who; «H« «.«H N«H« H.«N «.«H «N«« «.«N «.«H ««H« ««HofiHS «.« «H« N«HH «.« H.«H HN«H «.« «.«H EH «HHQS «Rmmoo « BI a; « >w| «SH « Bl 2; ««H««mm « N H Hem 8.330960 $33 98 .cofiflng mo uaflodmmoo 41.3.. .35302 w do «8.33m « um @30de coflEmHmoou «8g EIAVM "Hg 134 «.«H ««««H «.« «NH«H H.« «HHHN HEB. «.H «.H«H ««N «.N «.HH ««« «.H H.NoH Nom Ida: 8H «.HJIIIuBHHHmm «. H.H«H «« fldflflu «Hg «.NN «.«N H««« «.«N «.« «««« «.HH «.HH «««N 10813 «.«N «.«H «««« «.«« «.« «««« «.«H «.«H ««H« ««««Huom «H«HH? «43H H333 g 3% «gm Egg H. o HHH «H aflmfidw «38310 . gm“ «Emma «.H «.««H ««H «.H «.«H ««N m. «.««H ««H «flag ««.««Hmm «Hfiamd «.« H.NN ««« «.« «.« ««« H. «.H«H «H 3888 936090 «.«H «.«N «««H «.«H N.« «««H H.H «.«H ««N «HflmouHucoH «gamma N.HN «.«N H««N «.«H «.« «««N «.H «.«N ««« m« «@0830 «fig 3mooflo§ «Hing «030g x083 «. «.«« ««H «.H «.«H ««N «.N «.«N Ho« «28% «««H««.Hm «4686889 3359 «@320 «.« «.«N «N« H.N «.N« ««« «.« «.«H ««« $121513an3305 «.HH «.«N «««H H.NH H.« «««H «.«N «.NH «««« «ouHu «moHon N.«H «.«N H«HN «.«H «.« N««N «.«« «.HH «««« ««HOQOHQG H. «.««H HH «Hfi«8« Iago... «H.& N. O.N«H «« «H«H««« 8% mHfiHfioma mammaggfl «.« «.«H H«« «.N «.«N HN« N.N «.««H H«« «HHHoH« ««««p««Ha «. «.«« «NH «. «.HHH N« H.H «.H«H ««N «H«cmcoumfio «89%8 H: «.H«H cm a g «. «.H«H «H. «. «.«« ««H ««««E«« «25.5«3 «.HN «.«N «««N N.«N «.«H ««N« «.«« «.«N «««« «VH0 «894a «.«N «.«H «««« «.«N «.«H «««« «.«« «.«N N««« ««HofiHB «.« «.«N «««H N.« «.« «««H «.«H «.« N««N H«Hmsg «ommmoo m POI E; w >|UI 8; w .>|Ul ME; mmflommm « Jmfl « «8380 .«««H «35502 «l.«« «.56. 135 maximum densities of cyclopoid copepods (over 7,000/m3) were recorded at station four. Both of these copepod groups comprised a major portion<fiithe zooplankton. Rotifers also were a prominent taxon in the November samples, comprising from 14% to 39% of the fauna. Maximum densities (over 8,000/m3) occurred at station two. "I7'11@Hi’fli’flfiflmflflflfl'lfl'flfliflfl“