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I. . I . ..2 «III . III I I .I.. .I. I. . In I I III I . I... H .. H. II I . “I .I I II I. .Iu . . . I I I .I. .IIII I .I. I. IIIHII . I III. III . ..x. . I .. “l“ Will it \\ “ill“ LIBRARY Michigan Sm University This is to certify that the thesis entitled CRUSTACEAN ZOOPLANKTON OF LAKE LANSING, MICHIGAN presented by Fatimah Md.Yusoff has been accepted towards fulfillment of the requirements for M. S . degree in Fisheries and Wildlife M. wan‘aflfi U Major professor Date October 31, 1279 0-7639 ovmmuz PINES ARE 25¢ PER DAY PER um Return to book drop to remove this checkout from your record. I CRUSTACEAN ZOOPLANKTON OF LAKE LANSING, MICHIGAN By Fatimah Md.Yusoff 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 1979 ABSTRACT CRUSTACEAN ZOOPLANKTON OF LAKE LANSING, MICHIGAN By Fatimah Md.Yusoff The crustacean zooplankton of Lake Lansing, Michigan, were examined during 1978 and 1979. Twelve species of Cladocera and four species of Copepoda were found. Only nine species were common while the rest were found in quantities of less than three individuals per liter of water. The patterns of seasonal abundance of the common species were found to by typical of a number of lakes of similar climatic conditions. Lake Lansing was dominated by three small species; Bosmina longirostris during spring, Ceriodaphnia lacustris and Chgdorus sphaericus during summer. Analysis of a series of collections made over a 24-hour period suggested that some species of zooplankton underwent vertical migration despite the shallowness of the lake. "Dalam Kenangan Ayah ku" ii ACKNOWLEDGEMENTS My deepest gratitude and appreciation are extended to Dr. Clarence D. McNabb, my major professor, for his guidance and encouragement through- out this study. Special thanks are extendedto the other members of my graduate committee, Dr. Donald J. Hall and Dr. Charles R. Liston, for their assistance from time to time. I am also grateful for the assistance given to me by the graduate students in the Limnological Research Division. Special thanks are also due to John C. Craig for his timely help. My heartfelt thanks go to MARA (Malaysian Government Agency) who granted me scholarship and financial support to study in the United States. My deepest appreciation is also extended to Abang Dzul for his constant encouragement and moral support.. Resources for scientific work were provided by U. S. Environmental Protection Agency, Clean Lakes Program, under Grant No. R 80504601 to Michigan State University. iii TABLE OF CONTENTS Page LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . v LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . vi INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Lake Lansing at the Time of Study . . . . . . . . . . . . . . . 2 MATERIALS AND METHODS . . . . . . . . . . . . . . . . . . . . . . 9 RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Vertical Migration . . . . . . . . . . . . . . . . . . . . . . . 36 LITERATURE CITED . . . . .-. . . . . . . . . . . . . . . . . . . . 39 APPENDIX C O O O O O O O C O O O O C O O O O O O O O O O O O O O O 43 iv Table A24. LIST OF TABLES The total volume of each depth stratum sampled of Lake Lansing, Michigan . . . . . . . . . . . . . . . . Crustacean zooplankton species occurrence in Lake Lansing, Michigan, during 1978 and 1979 . . . . . . . . . . . . . Total densities (animals liter -1) of zooplankton on each sampling date for littoral and pelagial zones of Lake Lansing, Michigan, during 1978 and 1979 . . . . . . . Mean maximum length and brood size of selected monthly samples of crustacean zooplankton from Lake Lansing, Michigan. Values given are the mean i one standard error of the mean estimate . . . . . . . . . . . Densities (individuals 1-1) of cladoceran zooplankton species in the littoral zone of Lake Lansing, Michigan, during 1978 and 1979. Values given are the mean of six samples 1 one standard error of the mean estimate (ex- cept for May 22 and July 21, 1978, where n - 5) . . . Densities (individuals 1-1) of cyclopoid and calanoid co- pepods in the littoral zone of Lake Lansing, Michigan, during 1978 and 1979. Values given are the mean of six samples;i one standard error of the mean estimate (ex- cept for May 22 and July 21, 1978, where n - 5) . . . . Densities (number of individuals 1-1) of each zooplankton species in the pelagic zone of north basin of Lake Lansing, Michigan, during 1978 and 1979 . . . . . . . . . . . . . . Densities (number of individuals 1-1) of each zooplankton species in the pelagic zone of south basin of Lake Lansing, Michigan, during 1978 and 1979 . . . . . . . . . . . . Page 11 14 22 23 43 45 47 49 LIST OF FIGURES Figure 1. Bathmetry and sampling stations of Lake Lansing, Michigan. Depth contours in meters . . . . . . . . . . . . . . . . . Depth-time diagram of isotherms (°C) in the south basin of Lake Lansing, Michigan, during 1978 . . . . . . . . . . Depth-time diagram of isotherms (°C) in the north basin of Lake Lansing, Michigan, during 1978 . . . . . . . . . . . Depth-time diagram of isopleths of dissolved oxygen concen- tration in mg l.-1 in the south basin of Lake Lansing, Mi- chigan, during 1978 . . . . . . . . . . . . . . . . . . . Depth-time diagram of isopleths of dissolved oxygen concen- trations in mg 1'.1 in the north basin of Lake Lansing, Mi- chigan, during 1978 . . . . . . . . . . . . . . . . . . . Seasonal abundances (individuals liter -1) of Bosmina lon- girostris, Chydorus sphaericus and Ceriodaphnia lacustris in the littoral zone of Lake Lansing, Michigan, during 1978 pand 1979. Vertical bars indicate one standard error of the mean estimate . . . . . . . . . . . . . . . . . . . . . . Seasonal abundances (individuals liter -1) of Bosmina lon- girostris, Chydorus sphaericus and Ceriodaphnia lacustris in the pelagial zone of Lake Lansing, Michigan, during 1978 and 1979. Vertical bars indicate one standard error of the mean estimate . . . . . . . . . . . . . . . . . . . . . . Seasonal abundances (individuals liter -1) of Daphnia ga- leata mendotae, Daphnia retrocurva and Diaphanosoma leach- tenbergianum in the littoral zone of Lake Lansing, Michigan, during 1978 and 1979. Vertical bars indicate one standard error of the mean estimate . . . . . . . . . . . . . . . Seasonal abundances (individuals liter -1) of Daphnia ga- leata mendotae, Daphnia retrocurva and Diaphanosoma leach- tenbergianum in the pelagial zone of Lake Lansing, Michigan, during 1978 and 1979. Vertical bars indicate one standard error of the mean estimate . . . . . . . . . . .'. vi Page 15 16 17 18 10. ll. 12. l3. 14. 15. Seasonal abundances (individuals liter ‘1) of adult Cyclops bicuspidatus thomasi, cyclopoid juveniles and Diaptomus oregonensis in the littoral zone of Lake Lansing, Michigan, during 1978 and 1979. bars indicate one standard error of the mean estimate . Vertical Seasonal abundances (individuals liter-1) of adult Cyclops bicuspidatus thomasi, cyclopoid juveniles and Diaptomus oregonensis in the pelagial zone of Lake Lansing, Michigan, during 1978 and 1979. bars indicate one standard error of the mean estimate . Vertical Vertical distribution of Ceriodaphnia lacustris and Daphnia galeata mendotae in the north basin of Lake Lansing, Michigan, on July 30, 1978 . . Vertical distribution of Daphnia retrocurva and Diaphanosoma leuchtenbergianum in the north basin of Lake Lansing, Michigan, on July 30, 1978 . Vertical distribution of Chydorus sphaericus in the north basin of Lake Lansing, Michigan, on July 30, 1978 . Vertical distribution of Cyclopoid and Calanoid Cope- pods (Diaptomus oregonensis) in the north basin of Lake Lansing, Michigan, on July 30, 1978 . Structure of Daphnia. Lateral view of adult female. 2. Postabdomen of Daphnia galeata mendotae. 3. Head of Daphnia galeata mendotae. l. Daphnia galeata mendotae. 4. Daphnia retrocurva. Lateral view of adult female. 5. Head of Daphnia retrocurva. 6. Postabdomen of Daphnia retrocurva . . Structure of Bosmina and Chydorus. rostris. Lateral view of adult female. of Bosmina longirostris. 3. Chydorus sphaericus. La- teral view of adult female. 4. Postabdomen of Chydorus sphaericus . . . . . . 1. Bosmina longi- 2. Postabdomen Structure of Ceriodaphnia and Acroperus. daphnia lacustris. Lateral view of adult female. 2. Acroperus harpae. Lateral view of adult female. 3. Postabdomen of Acroperus harpae . Structure of Sididae. view of adult female. 2. Diaphanosoma leuchtenbergianum Lateral view of adult female . 1. Carla- l. Sida crystallina. Lateral (Structure of Cyclops bicuspidatus thomasi. 1. Dorsal view of Cyclops bicuspidatus thomasi. 2. Fifth leg of Cyclops bicuspidatus thomasi. 3. Head of male Cyclops bicuspidatus thomasi . vii 19 20 25 26 27 28 52 54 56 58 6O Ar6. Structure of Diaptomus oregonensis. 1. Lateral view of Diaptomus oregonensis. 2. Fifth legs of female Diaptomus oregonensis. 3. Fifth legs of male Diaptomus oregonensis . viii 62 INTRODUCTION The crustacean zooplankton constitute one of the trophic links be- tween algae and the fish that dominate the higher trophic levels of the aquatic ecosystems. According to Nowak (l975),in eutrophic lakes, zoo- plankton is the essential link between phytoplankton and the bacteria and is responsible for rapid turnover of substances. Nearly all fish subsist on zooplankton shortly after they hatch and commence feeding (Galbraith 1967; Noble 1975). In addition, zooplankton form a very important food item for invertebrate predators (Cummins gt 31. 1959; Hall 1964; Kerfoot 1977; Wells 1970). The composition and abundance of the zooplankton are therefore important aspects in the ecology of lacustrine ecosystems. Like some aquatic insects, certain species of zooplankton are use- ful indicators of changing environments. Several studies have shown that a shift from Eubosmina coregoni to smaller Bosmina longirostris is an indication of eutrophication. In a study of the sediments of Linsley Pond, Connecticut, Deevey (1942) recorded that microfossils of Eubosmina coregoni were replaced by Bosmina longirostris at about the level of sediment deposited when the lake became highly productive. (A general consequence of the enrichment of lake ecosystems has been the increase in the standing crop of blue green algae. Large colonies of these can- not be utilized by most planktonic herbivores.l However, Chydorus sphaericus can feed upon these algae. Thus, the appearance of C. sphaericus provides one of the most characteristic changes in planktonic samples as waters become strongly enriched with nutrients (Brooks 1969). The purpose of this study is to present an analysis of the crusta- cean zooplankton occurring in Lake Lansing during 1978 and 1979. The U. S. Environmental Protection Agency has implemented dredging as a lake restoration technique, a project which will remove the nutrient-rich sediments and will deepen the littoral zone of the lake. Since this study was part of the predredging program on Lake Lansing, the data ob- tained will provide a useful historical comparison with the data during the post-dredging era, thus demonstrating the effect of dredging on the zooplankton communities in this lake. Lake Lansing at the Time of Study Created through the processes of glacial scouring and recession, Lake Lansing is located approximately 5-6 km northeast of the City of East Lansing in Meridian Township, Ingham County, T4N, RlW, Sections 2, 3, 10 and 11. The lake occupies an area of approximately 183 hec- tares, has a perimeter of about 6 km and a volume of 5 x 106 m3. It is, generally shallow, averaging 2.7 m in depth and has a maximum depth of about 11 m. A bar of glacial till divides the lake into north and south basins (Figure l). The water in the lake is virtually standing with surface winds, rather than stream flow being responsible for the mixing that occurs. In addition to precipitation on the surface, water enters the lake principally via overland flows and seepage through surrounding marsh lands. The littoral zone of the lake, defined as the depth to which rooted aquatic macrophytes grow, extended to the 3.0 m contour. The truly Outlet Figure 1. South Basin Bathymetry and sampling stations of Lake Lansing, Michigan. Depth contours in meters. 4 open-water pelagial region of the lake was confined to only 23% of the surface, while the littoral occupied the remaining 77%. The shore vege- tation mainly consisted of Lythrum salicaria, Typha angustifolia and Dryopteris thelypteris. The north basin of the lake is characterized by a mixed vascular hydrophyte population including Myriophyllum spp., Heteranthera dubia, Ceratophyllum demersum and vallisneria americana; a Chara globularis-Najas flexilis association dominates the submersed macrophyte community in the south basin. Seasonal variations of the temperature during the investigation appear in Figures 2 to 3. The lake was covered with ice from the be— ginning of December to the middle of March in the winter of 1978-79. A thermocline was established during May 1978 and tended to remain until September. The maximum temperature, 25° C, was found in the surface water in mid-June. A maximum sechi disk transparency of 1.20 m was found in early April 1978; a minimum.of 0.85 m occurred in May 1979. In the hypolimnion, total absence of oxygen was observed from mid-May to mid-September (Figures 4-5). .wnma msfiusv .smeSUHz .wcwmcma was; mo cameo nusom ecu ca Avov mahmnuoma mo Enuwmam oawulcueon mmm2w>oz mumOhuo mum—zmhhum ...msozc. >42. uzsm .N ouswfim >42 (W) H1d30 .mnma weapon .cmmwnuaz .mGHmGMA oxmq we :«mmn nuke: mnu cw Acov mauozuomfi mo Enuwmwv mEHuISumoa zmmzuhmum .532? >153 wzas .m ousmwm >42 no u- o co (“‘)H.Ld30 GI nuaom onu cw mmmzu>oz H .wnaa mceuom .cmwficoaz .mcamcna oxma mo sumac H we :H coeumuucoocoo cowaxo mo>aommqm mo mauoaaoma mo snowmen oaaulnumon mmmOHoo mum} mhmum .5302 >42. ~22. .q ouowem ><2 (W) Hld30 .mnma weapon .cnmfinoez .wcamcmq axed no cause sumo: one as HIH we cw mcofiumuucoocoo cowhxo om>aommwm mo onuoamomw mo amuwmam oaaulcumon .m muswfim zwmzu>oz - mung—.00 mumthmmm .5393 >42. wzam >42 4. . 1 -\ K) (O F- ‘- c N) OJ A.__9L_ (W) HidBO MATERIALS AND METHODS Samples were collected from May 22 through November 7, 1978, and from April 13 through May 11, 1979. Intervals between sampling visits averaged 11 to 14 days. Sampling generally began in the afternoon and the process took 2 to 3 hours to complete. Samples were taken at two stations in the pelagial zone, and at single points on six transects that serve as locations for sampling various parameters in the littoral zone (Figure 1). In the deep holes at the north and south basins, samples were collected at l, 3, 5 and 7 meters. On the transects, col- lections were made at l m depth over the 2 m contour. Sampling sites were located using permanent landmarks and a sonic depth finder. Samples were collected using a Schnidler-Patalas plankton trap made from plexiglas to reduce avoidance by the zooplankton. It had a 50 liter capacity and was equipped with a No. 20 net with apertures of 0.076 mm. The trap could be lifted and lowered into the water using a pulley system. Zooplankton samples were washed from the net with dis- tilled water into labelled glass bottles and were narcotized with tonic water (to relax the animals and thus minimize contortions) prior to pre- servation in 4% solution of 37% commercial formalin. In the laboratory, the formalin solution was replaced by 96% al- cohol to which 40 m1 glycerol per liter alcohol had been added. This prevented the organisms from becoming brittle. Late in the study, the same solution was used as a fixative in the field because formalin 10 solution caused extrusion of eggs from the brood pouch of the animals. Haney and Hall (1973) and Prepas (1978) describe techniques for better preservation of eggs in the brood chamber. Preserved samples were con- centrated to a known volume, usually 80 to 150 m1 depending on the den- sity of the animals, before sub-sampling. The contents of each sample bottle were poured into a beaker and were randomized by gentle mixing with a magnetic stirrer. A subsample of 1-10 ml was removed with a wide-mouthed Hensen—Stampel pipette and placed in a chambered counting cell (Gannon 1971). This technique of randomization was based on the results of a chi-square test for random- ness used by Duffy (1975). The entire cell was counted using magnifica- tions of 14x to 60x. When available, at least 100 animals were counted for each sample. Crustaceans were identified to species except immature cyclopoid copepods which were combined to form a single category. The taxonomy followed Pennak (1978) and Ward and Whipple (1959). All counts were adjusted so that they were on a basis of organisms per liter of water. Since the size of organisms and brood size of organisms reflect the availability of food and energy in aquatic system (Hall 1964), adults of Bosmina longirostris, Daphnia galeata mendotae, Daphnia retrocurva, Ceriodaphnia lacustris and Diaptomus oregonensis were randomly measured and examined for eggs and ephippia for each month of the sampling season. When available, at least 20 animals of each species were considered. For the analysis of seasonal abundances, a mean number of indivi- duals per liter for each common species from the littoral zone was ob— tained from counts of samples from the six transects. For the deep holes, the weighted mean of zooplankton density was obtained using the formula, 11 where D a weighted mean density in individuals per liter; di - zooplankton density in each stratum; vi a percent volume of each stratum (Table 1). Since there was no striking difference of animals between north and south basins (Appendix Tables Ae3 - Ar4), the data from these two sites were averaged, giving one mean representative of the pelagial zone of the lake. Table 1. The total volume of each depth stratum sampled of Lake Lansing, Michigan. Site Sample Depth Volume Percent depth strata (m3) volume (In) (In) . North 1 0-2 601184 36' 3331“ 3 2-4 593896 36 5 4-6 360167 22 7 6-Bottom 104000 06 South 1 0-2 177776 ‘ 37 3331“ 3 2-4 177546 37 5 4-6 106333 22 7 6-Bottom 21500 04 For the purpose of providing a permanent record of organisms for the natural history of the lake over a period of time, stained per- manent mounts were made using paracarmine and permount. These perm- manent slides were labelled and filed in the voucher collection of the Limnology Laboratory of the Department of Fisheries and Wildlife. A 12 set of photomicrographs and drawings showing diagnostic features of the whole or dissected organisms were also placed in the collection. The drawings were made with the aid of a compound microscope (magnification 100-400x). Measurements were made in microns (u). The drawings are in- cluded here as Figures 1 through 6 of the Appendix. Vertical migration is a very conspicuous feature in planktonic crustaceans. For the analysis of this phenomenon, six series of col- lections were made over a 24-hour period on July 30, 1978, at approxi- mately 4-hour intervals from.dawn until midnight in the north basin of Lake Lansing at various depths (surface, 2, 4, 6 and 8m). Samples were collected, identified and counted using the same method as above. RESULTS Table 2 presents the list of species of crustacean zOOp1ankton found in Lake Lansing during the study. A total of 16 species were identified: 12 cladocerans and 4 copepods. Inspection of the quanti- tative counts in the Appendix Tables A91 through Ar4, reveals that Daphnia parvula, Daphnia pulex, Leydigia quadrangularis, Sida crystal- lina, Mesocyclops edax and Tropocyclops prasinus were present only in minute quantities; therefore, these were not included in the discus— sion of seasonal abundance that follows. Figures 6 through 11 show the seasonal distribution of the common species for both the littoral and pelagial zones. Comparing these, more species were found in the former. Sida crystallina was exclusively found in the littoral zone. Tonolli (1958) found that this large cla- doceran was most abundant just off weed beds, often hanging suspended from the littoral vegetation, especially Potamogeton spp. Chydorids such as Acroperus harpae and Leydigia quadrangularis were found prin- cipally in the littoral of the lake. A small number of these were found in the limnetic (Appendix Tables Ar3 - Ar4), probably being swept there by currents. Being typically limnetic, species of Daphnia were most abundant in the pelagial zone of Lake Lansing. However, a significant number of these were present in the littoral samples (Figure 8). For the rest of the zooplankters, the density and the seasonal fluctuation of each species were more or less similar in both locations. 13 14 Table 2. Crustacean zooplankton species occurrence in Lake Lansing, Michigan, during 1978 and 1979. Daphnia Daphnia galeata mendotae Birge Daphnia parvula Fordyce Daphnia pulex Leydig Daphnia retrocurva Forbes Other Cladocera Acroperus harpae Baird Bosmina longirostris (O.F.M.) Ceriodaphnia lacustris Birge Chydorus sphaericus (O.F.M.) Diaphanosoma leuchtenbergianum Fischer Leptodora kindtii (Focke) Leydigia quadrangularis (Leydig) Sida crystallina (O.F.M.) Calanoid copepods Diaptomus oregonensis Lillj. Cyclopoid copepods Cyclops bicuspidatus thomasi Forbes Mesocyclops edax Forbes Trapocyclops prasinus (Fischer) 220 " 200- I80 " ISO “' l20 - I00 I" INDIVIDUALS / LITER NO- 60" 4o - 20h- Figure 6. 15 A. lawman hmumnau o canon: spacer/cw o CkwhduMnb hnmwwb I 6/I 9/2I 7/" T/3I 9/20 9/9 9/29 IO/l9 II/B 4/I3 5/3 5/23 IOTD I979 Seasonal abundances (individuals liter -1) of Bosmina longi- rostris, Chydorus sphaericus and Ceriodaphnia lacustris in the littoral zone of Lake Lansing, Michigan, during 1978 and 1979. Vertical bars indicate one standard error of the mean estimate. 16 use _ IA lumfln'kmyWnMi I O CMMMnn.umean Iso - O cmmm locum: NO' INDIVIDUALS / LITER 6/l 5/2I 7/II 7/3I 5/20 9/9 9/29 IO/I9 Ill! 4/I3 5/3 5/23 I975 I979 Figure 7. Seasonal abundances (individuals liter -1) of Bosmina longi- rostris, Chydorus sphaericus and Ceriodaphnia lacustris in the pelagial zone of Lake Lansing, Michigan, during 1978 and 1979. Vertical bars indicate one standard error of the mean estimate. 17 221- 20 _ A Demo when mondolao ' j 0 Donnie rune-urn la ‘ ' O 01017000030070 ImMonbory’onum l2- INDIVIDUALS / LITER / ND° O I O 1 O 1 1 1 1 1 1 5/! 5/2I 7/II 7/3I 5/20 9/9 9/29 IO/I9 II/D 4/I3 5/3 5/23 I979 I979 Figure 8. Seasonal abundances (individuals liter -1) of Daphnia galeata mendotae, Daphnia retrocurva and Diaphanosoma leuchtenber- gianum in the littoral zone of Lake Lansing, Michigan, during 1978 and 1979. Vertical bars indicate one standard error of the mean estimate. 22 I2 INDIVIDUALS I LITER ND' Figure 18 r 1' A1 aquo admnvlmnmnnn o IMHWMbIHMWQWM' - \ ‘0 waMmammo.Mmmnmuanmn I - I. l ‘1 1 \ x P O ' I l l ' .' \r 1 ' 1 L g 1 1 1 AA 1 1. 6/l 6/21 7/11 7/31 8/20 9/9 9/29 lO/ls Il/B 4/l3 5/3 5/23 1978 I 1979 ' -l . 9. Seasonal abundances (individuals liter ) of Daphnia galeata mendotae, Daphnia retrocurva and Diaphanosoma leuchtenber- gianum in the pelagial zone of Lake Lansing, Michigan, during 1978 and 1979. Vertical bars indicate one standard error of the mean estimate. 19 A Adult Cyclops 01¢:pron Mamas! 50 b o Cyclopoid junnuu ‘5 II o Dicpromu: element‘s w I- 35 '- c O {1' :3 30 L \ x 3 I g _ \ e 25 \ > 1 § \ - 20- l 0 o 2 l . . o / ’ '5 " f K / . V ‘ IO - . . ' 9,7 . '.' 5 n- O 1 1 1 1 1 L1 \l\_ 1 1 SI! 9/2I 7/II 7/3I 9/20 9/9 9/29 lO/I9 ll/5 4/I3 5/3 5/23 1973 I 1979 Figure 10. Seasonal abundances (individuals liter -1) of adult Cyclops bicuspidatus thomasi, cyclopoid juveniles and Diaptomus _- oregonensiinn the littoral zone of Lake Lansing, Michigan, during 1978 and 1979. Vertical bars indicate one standard error of the mean estimate. 20 55 __ A Adult Cyclops pinup/dam: mam",- , o Cyclopoid juveniIes I o ‘71me arena/Ions]: 40L 351- I 25“ 20" INDIVIDUALS / LITER NO' o 1 1 1 1 1 1 1 .\/\ 1 1 1 G/I G/ZI 7/” 7/3I 3/20 9/9 9/29 IO/l9 III. 4/I3 5/3 5/23 I978 I979 Figure 11. Seasonal abundances (individuals liter -1) of adult Cyclops bicuspidatus thomasi, cyclopoid juveniles and Diaptomus oregonensis in the pelagial zone of Lake Lansing, Michigan, during 1978 and 1979. Vertical bars indicate one standard error of the mean estimate. 21 In spring, Bosmina longirostris was the dominant species, consti- tuting about 53% of the total number of zooplankters. In summer and fall samples, however, Chydorus sphaericus was most abundant. In gene- ral, spring was the time of greatest total density. In the pelagial zone, a second peak of total abundance took place in September. That was during the fall turnover (Table 3). In the littoral zone, on the other hand, a second pulse started in mid-July and continued until Sep- tember. The lowest total density was found on April 13, 1979. The average number of eggs per clutch of Bosmina longirostris, Daphnia galeata mendotae, Daphnia retrocurva, Ceriodaphnia lacustris and Diaptomus oregonensis is shown in Table 4. B. longirostris and C. lacustris had the largest brood size in April, while this occurred in the rest of the species in May. Generally, the time of largest brood size corresponded to the time of largest body size, except in D. retrocurva where largest individuals were found in early November. The helmet of this species was large at that time of the year. Figures 12 through 15 illustrate the relative abundance of 7 species at different times of the day and at different depths. In general, the greatest in number of these organisms was found in the upper layer of the lake during low light intensity (dusk and dawn) and in the deeper depths during high light intensity of the day. 22 Table 3. Total densities (animals liter-1) of zooplankton on each sampling date for littoral and pelagial zones of Lake Lansing, Michigan, during 1978 and 1979. Date Littoral zone Pelagial zone 5/22/78 171 278 6/1/78 165 163 6/19/78 71 66 6/30/78 121 100 7/10/78 140 148 7/21/78 249 136 8/2/78 140 164 8/12/78 226 195 8/24/78 192 192 9/6/78 207 201 9/20/78 181 155 10/3/78 152 198 10/16/78 146 136 10/26/78 129 111 11/7/78 98 115 4/13/79 26 53 4/26/79 76 71 5/14/79 474 345 23 Table 4. Mean maximum length and brood size of selected monthly samples of crustacean zooplankton from Lake Lansing, Michigan. given are the mean i_one standard error of the mean estimate. Values Species and Months Maximum Brood length size (M) Bosmina longirostris June 1978 0 5119.01 1.33:0.21 July 1978 Sample unavailable August 1978 Sample unavailable September 1978 0 33:0.02 1.75:0.25 October 1978 0.36:0.01 1.55:0.16 November 1978 0.40:0.01 2.45:0.16 April 1979 0.55:0.01 6.15:0.41 May 1979 0.48:9.01 4.33:0.50 Daphnia galeata mendotae June 1978 1.08:9.03 3.00:0.25 July 1978 1.06:0.04 2.63:0.26 August 1978 1.05:0.02 2.25:0.13 September 1978 1.09:0.02 2.43:0.28 October 1978 1.07:0.03 2.76:0.19 November 1978 1.06:0.02 3.75:0.25 April 1979 1.03:0.01 5.67:0.88 May 1979 1.12:0.07 7.40:0.93 Daphnia retrocurva June 1978 1.10:0.04 2.57:9.32 July 1978 1.09:0.03 2.00:0.00 August 1978 1.00:0.01 2.00:0.00 September 1978 1.04:0.02 2.55:0.28 October 1978 1.09:0.01 2.08:0.08 ephippia November 1978 1.15:0.02 2.50:0.34 ephippia April 1979 Sample unavailable May 1979 1.10:0.08 3.50:0.50 Ceriodaphnia lacustris ' June 1978 0.58:0.02 3.50:0.40 July 1978 0.57:0.01 2.14:9.14 August 1978 0.57:0.01 2.06:0.11 September 1978 0.58:9.02 2.00:0.00 October 1978 0.56:0.01 2.00:0.00 November 1978 0.59:0.02 ephippia April 1979 0.68:0.02 8.33:0.45 May 1979 0.65:0.01 6.80:0.45 Table 4 (con't.) 24 Diaptomus oregonensis June 1978 July 1978 August 1978 September 1978 October 1978 November 1978 April 1979 May 1979 SampIe unavailable 1.38:0.04 OCDQNUI 28. .33:0.27 5010.50 .17:0.70 .173-_0.70 5010.50 3310.66 5010.15 25 .meaa .om sane co .ammaeuez .waamamo uses no shame sauce was as mmuomcms mummamm owncmun mam mfluumzomw owccmmoOMHmU mo coauanwuumwo Hmofiuuo> .NH ouawem Lace—MES ..2. 8882:. a» mu m. a .2858 38:3 SESS #332: Seems-Que.“ :1: . ., _,.iw .. L, 4_ ...l T 8.. 2..“ 8a. 8.: 8.9 . 86 ugh (”I H1630 26 .msma .om mama so .cowacoaz .wcfimcma mama mo canon cuuo: ecu ca fiancee xhoncouc030~ msomosmcmowa mom m>usoouuou penance mo cowunowuumfio Hmowuuo> .MH ouswam .22: 038 .8 6832:. . figeusueeéegse m am J. o quuoeuemua 1 9. Lance: accuse USE. U") H1430 27 .meme .om sass co .cmwseoaz .waamcmq mxmq mo canon Soho: onu ow mzowummamm mahoomco mo coausnfiuumwu Hmowuuo> .eH museum .22: £80 .2. 88.85. 1 mm. ow. mm o... o massages» 328.3.» w}: (W) H1430 28 .wmma .om xasw co .smwazuwz .mcamcmq oxmq mo cameo coho: ecu ca Awemzm: 10mmho mascummwnv mvomomoo vfionmamo mom owomoaoho mo cofiunnwuumfiv Hmofiuuo> .ma shaman .22. 938 .2. 88.85. m u . 353823 2.3383 J : ._ co m. 8.2.220 b. mi: 11 l HLdBO ) (In DISCUSSION Changes in the seasonal abundance are quite variable among species and within species of crustacean zooplankters. According to Hutchinson (1967) there are essentially three main types of life histories in the cladocerans. Perennial species overwinter in low population densities as free swimming adults rather than resting eggs. These species may exhibit one, two or more irregular maxima. Perennial species that ex- hibit maxima in the surface layer only during the colder period in spring or fall, and in the cooler hypolimnion and metalimnion during summer stratification, are known as cold-water species. The aestival species that have a distinct diapause in resting eggs commonly develop popula- tion maxima in the late spring, usually during the time when the water is warmest or a little after that time. Although one population maximum is typical, a second peak often occurs in fall. In Lake Lansing, Daphnia retrocurva, Diaphanosoma leuchtenberyia- mum and Ceriodaphnia lacustris could be classified as aestival species. Appearing in a small number in May, D. retrocurva reached a maximum in September (Figures 8 and 9). There was a second pulse observed in the limnetic population in mid-October when ephippial eggs were produced. The population sharply declined after the second pulse. Birge (1898) working on Lake Mendota found the same seasonal succession for the species, whereas Wells (1960) found no ephippia in Lake Michigan though he supposed the species to survive the winter as resting eggs. Clark 29 30 and Carter (1974) reported that D. retrocurva began to peak at the end of August and declined by late October, with the production of a few ephippia. A monocyclic species, Ceriodaphnia lacustris appeared sporadically in late spring and multiplied to produce a large population in July and August when the water was warmest (Figures 6 and 7). With some fluc- tuations, numbers declined in September and the species almost disap- peared from the lake by early November. Resting eggs were produced in late October and November (Table 4). The pOpulation was presumably re- cruited from these in the following spring. Kwik and Carter (1975) have found comparable behavior in Ceriodaphnia quadrangula in a beaver pond near Georgian Bay, Ontario. The population of Diaphanosoma leuchtenbergianum began to increase in June and expanded rapidly until it reached a seasonal maximum of 23 liter -1 on July 21, 1978 (Figures 8 and 9). The numbers steadily de- clined after a smaller peak in late August and the population dis- appeared in late October. D. leuchtenbergianum has been found charac- teristically to be most abundant in summer throughout the temperate region. Clark and Carter (1974) found that D. leuchtenbergainum reached the seasonal peak in August and numbers were reduced to almost zero at the end of October. In most of such studies, there is usually a single striking summer maximum, a little after the warmest period, during which time the growth of the papulation is supposed to be rapid. In Lake Lansing, however, a well marked minimum in late July separated the two maxima in July and August (Figures 8 and 9). The reason for this dif- ference from the typical pattern is not explained by the data of this study. 31 The population of Chydorus sphaericus peaked in early May and dropped to a low level in early June, after which it began to rise again and remained high until September. At the height of summer (July and August) a larger density of this species was found in the littoral than in the pelagial zone. With some fluctuations, the population be- gan to decline in September (Figures 6 and 7). Borecky (1956), studying population density of cladocerans in Pymatuning Reservoir, reported that C. sphaericus were present in substantial numbers throughout the year, but reached their maximum in July and August when they numbered as high as several thousands of organisms per liter. Generally, chydorids live principally in the littoral of lakes (Keen 1973). In Lake Lansing, how- ever, C. sphaericus is found in both the littoral and pelagial zones. According to Brooks (1969) this species is usually absent from open waters, but often appears in enormous numbers during a bloom of blue green algae. Probably due to the same reason, Birge (1898) found C. sphaericus to be perennial in the littoral but appeared in great quan- tity in the open water only during summer. In Lake Lansing, Bosmina longirostris exhibited characteristics of a cold water species. They greatly out-numbered other species in the spring, but declined sharply as the water got warmer in summer (Figures 6 and 7). The individuals and broods were largest in the spring (Table 4). The population recovered in late September. Povich (1978) found this species was the most abundant in the winter samples. Berg and Nygaard (in Hutchinson 1967) showed that the maximum of B. longirostris occurred in May at the time of the phytoplankton maximum; Scenedesmus armatus var. chodatii and diatoms were most common. B. longirostris in Pymatuning Reservoir (Borecky 1956) reached their highest numbers 32 (1000 or more per liter) in the middle of May with a smaller peak about mid-July. Kwik and Carter (1975), on the other hand, found that this species in a predation free pond had three pulses with a tendency for sudden numerical increase followed by a.rapid decline. Presumably this represented an overshooting of the carrying capacity of a food limited environment lacking the dampening effects of predation. It seems, there- fore, that B. longirostris is a variable species and its population fluc- tuations vary with time and environmental conditions. According to Wesenberg—Lund (in Kwik and Carter 1975), B. longirostris is a versatile animal since it occupies virtually every type of fresh-water habitat and is known to migrate between limnoplankton and littoral as physical con- ditions change. In the case of Lake Lansing, there is a possibility that the apparent crashes of B. longirostris in summer may be due to the pre- dation of fish and invertebrates, or the animals may have temporarily migrated to the bottom sediments. Such behavior might be attributed to food shortages because of the competition with other zooplankters such as C. sphaericus, C. lacustris and D. leuchtenbergianum which were abundant in summer. By retreating to the benthos, B. longirostris might have ac- cess to food unavailable to other animals (Kwik and Carter 1975). The importance of detritus and bacteria as zooplankton food has been sug- gestedby many authors (e.g., Edmondson 1957; Peterson ggngl. 1978). Daphnia galeata mendotae behaved in Lake Lansing as a perennial species with a more or less diacmic cycle. In the pelagial zone, a marked increase in the population to a maximum in spring (12 Daphnia liter-1) was followed by irregular oscillations which culminated in a second maximum in early November (Figure 9). In the littoral, the sea- sonal pulses were not sharply defined (Figure 8). D. galeata mendotae 33 had large broods, containing as many as 7.4 eggs per brood in May (Table 4). This obviously reflected the availability of food at that time. Hall (1964) found that the average brood size of this species ranged between 2 and 4 eggs per adult female throughout much of the reproductive season. Some effects of competition with D. retrocurva, which outnumbered D. galeata mendotae at its maximum in September, may also have been involved in the depression of the latter species at that time. The second pulse of D. galeata mendotae did not show until Noveme ber. Tappa (1965), in a study of Aziscoos Lake in Maine, found that D. galeata mendotae was better adapted to cooler temperature and thus be- came less common at the height of summer. Besides high temperature, decline of the Daphnia population in Lake Lansing in summer could also have resulted from high density of aestival Diaphanosoma leuchtenbergia- num (Figures 8 and 9). D. galeata mendotae appears to exhibit a com- parable behavior in other localities, especially Pymatuning Reservoir (Borecky 1956) and Base Line Lake, Michigan (Hall 1964). Hall found a relatively large number of these individuals present throughout winter. On the other hand, Threlkeld (1979), studying in Wintergreen Lake, Michigan, found that D. galeata mendotae had only one maximum density in mid-July and the population disappeared by late July. He attributed the midsummer decline of Daphnia population in this lake to a size-selec- tive predation by planktivorous fish. Two orders of free-living fresh-water copepods were found in Lake Lansing; Cyclopoida and Calanoida. At any time of the year, cyclopoid juveniles were always more numerous than the adults. Since Cyclops bicuspidatus thomasi was the only abundant cyclopoid species, it can be presumed that most of these copepodites belonged to this species. C. 34 bicuspidatus thomasi was the first copepod present in large number in the spring, presumably emerged from the diapause cycle after the ice departed and the water became oxygenated. After early June, however, this population rapidly declined and remained low until it began to in- crease again in September (Figures 10 and 11). In mid-summer the in- crease in the number of juveniles did not result in an increase in the number of adults. The decrease in adult population may have been due to predation by fish. Brooks (1969) reported that of the copepods, C. bicuspidatus was the most commonly eaten species in summer. Also, the low population of this species could have been due to diapause in the mud in a cocoon-like cyst during the stage of copepodite IV. Birge and Juday (1908) discovered that C. bicuspidatus encysted in the mud of Lake Mendota from June to September. The same phenomenon has subse- quently been discovered in Douglas Lake, Michigan and Crystal Lake, Minnesota (Moore 1939; Cole 1953). It could be due to the same reason that C. bicuspidatus thomasi has been uncommon in summer in other small bodies of water (Marsh 1903; Plew and Pennak 1949). Diaptomus oregonensis was the only calanoid species found in Lake Lansing. The population went through a spring pulse in early June during the decline of C. bicuspidatus thomasi. Two smaller maxima oc- curred in August and October, after which the population density de- clined steadily (Figures 10 and 11). Absence of D. oregonensis in win- ter led Lai and Carter (1970) to believe that this species survived this period as resting eggs on the bottom of the lake, possibly due to food scarcity. In general, the number of species found in Lake Lansing was in the range of mesotrophic lakes, 6-18 species (mean 11.8) mentioned by Patalas 35 and Patalas (1966). Most remarkable was the presence in high densities of small cladoceran species, e.g., Bosmina longirostris, Ceriodaphnia lacustris and Chydorus sphaericus. This suggests that predation was important in eliminating larger zooplankters such as Daphnia which was present in relatively small density. Brooks and Dodson (1965) demon- strated that when Crystal Lake, Connecticut, was invaded by plankti- vorous fish, Alosa aestivalis, the larger forms of zooplankton were replaced by much smaller forms of Bosmina, Tropocyclops and Cyclops. Fish population assessment was not made for Lake Lansing but the Chaoborus population was as high as 678 animals mfz in the spring (Siami 1979). Beside predation, fluctuations in zooplankton populations could have also been due to changing food conditions, increased water tempera- ture and competition between species. Most zooplankters exhibit high population density and brood size in spring when food is abundant and water temperature is optimum; the effect of competition may thus be inhibited. Numbers, however, decline as the food supply is exhausted. Probably due to competition, Daphnia parvula and Daphnia pulex were only found in spring and fall when food was abundant (Appendix Tables A91 - Ae4). In Aziscoos Lake in Maine, Tappa (1965) found six species of Daphnia, the greatest taxocene of this genus known anywhere. Due to competition, only D. galeata mendotae and D. catawba dominate the water column of that lake. In Lake Lansing, species such as Chydorus sphaeri- cus, Ceriodaphnia lacustris and Diaphanosoma leuchtenbergianum may have continued to increase in summer because they were able to utilize the food resources that were present during that season. In order to 36 evaluate such relationships, a detailed examination of phytoplankton abundance and food preferences of these species is needed. In recapitulation, it can be said that enrichment of lakes can promote increase in the standing crop of phytoplankton, thus leading to an increase in the density and biomass of zooplankton. However, the composition and abundance of zooplankters apparently seldom suffer major modification by such enrichment alone. In most lakes the compo- . sition and oscillations of zOOplankton are largely controlled by the degree and kind of predation, physical and chemical factors and compe- tition for food and space among planktonic animals themselves. Vertical Migration Even though Lake Lansing is a small shallow lake, certain patterns of vertical distribution of zooplankton could be observed as shown in Figures 12 through 15. The phenomenon, however, was not as striking as that found in transparent deep lakes (Kikuchi 1930). The majority of the species, with the exception of Diaphanosoma leuchtenbergianum which did not have morning maximum and Daphnia galeata mendotae which did not exhibit evening maximum, tended to rise at dawn and dusk into more superficial layers of the lake. At dawn, cyclopoid cOpepods, Daphnia galeata mendotae, Daphnia retrocurva, Ceriodaphnia lacustris, Chydorus sphaericus and Diaptomus oregonensis appeared to be maximum at the surface. Later at 1000 hours, as the light intensity increased, there was a tendency for most species to swim downwards. At 1400 hours, when the light intensity was highest, the number of organisms was found to be largest in the cooler depths between 2 and 8 m. During the sun— set, most of the species were found to be maximum at the surface. The 37 exception was Daphnia galeata mendotae which rose later after dark. It seems that light intensity with its regular rhythmical changes between day and night was an important factor controlling vertical movement of the zooplankters. McNaught and Hasler (1964) found that in most cases, a linear relationship exists between the rate of vertical movement and the rate of change in the logarithm of light intensity. Harris (1953) suggested that the daytime distribution and vertical migration patterns of many species of zooplankton is best explained on the assumption that each species is concentrated around a light optimum during the day, and that as the optimum light intensity moves toward the surface with the fading light of late afternoon and evening, the organisms follow. At night the stimulus for the upward migration is removed and the animals would move more or less at random. The data, however, shows that Cerio- daphnia lacustris and cyclopoid copepods had a tendency for downward movement at 0100 hour, probably due to what Kikuchi (1930) called posi— tive geogropism in darkness. In Daphnia, there was a marked tendency for more even distribution from the surface downward at this hour (Figures 12 and 13). Some workers have attempted to explain vertical movement in the zooplankton partly on the assumption that the animals feed on phyto- plankton in the upper layers during the night, and that excess weight due to feeding'causes an increase in their density so that they drop to deeper levels during the day. McNaught (1966) suggested that upper waters are food rich, but dangerous by day, herbivores are forced to secure their food there by night, and carnivores therefore would follow the behavior of their food species. McLaren (1963), however, hypo- thesized that the animals rise to feed in the warmer, productive upper 38 photic layers and then descend to the colder depths to slow down their metabolism, thus conserving energy for egg production. While vertical migration is a conspicuous characteristic of most planktonic populations, there is no evidence to believe that the same factors are acting in different populations in different environments. At present, a more thorough understanding of the adaptive functions of vertical migration awaits further research in this field. LITERATURE CITED Beeton, A.M. 1960. The vertical migration of Mysis relicta in lakes Huron and Michigan. J. Fish. Res. Ed. Can. 17:517-539. . 1965. Eutrophication of the St. Lawrence Great Lakes. Limnol. Oceanogr. 10:240-254. Birge, E.A. 1898. Plankton studies on Lake Mendota. II. The crus- tacean of the plankton from 1894 to December 1896. Trans. Wis. Acad. Sci. Arts. Lett., 11:274-451. Birge, E.A., and C. Juday. 1908. A summer resting stage in the deve- lopment of Cyclops bicuspidatus Claus. Trans. Wis. Acad. Sci. Arts. Lett., 16:1-9. Borecky, G.W. 1956. Population density of the limnetic Cladocera of Pymatuning Reservoir. Ecology. 37:719-727. Bosselmann, S. 1974. The crustacean plankton of Lake Esrom. Arch. Hydrobiol. 74:18-31. Brooks, J.L. 1957. The systematics of North America Daphnia. Mem. Conn. Acad. Arts Sci., 13:5-180. 1969. Eutrophication and changes in the composition of the z00plankton. Pages 236-255 in Eutrophication: Causes, Consequences, Correctives. National Academy of Sciences, Washing- ton, District of Columbia, USA. Brooks, J.L., and 8.1. Dodson. 1965. Predation, body size, and compo- sition of plankton. Science. 150:28-35. Clark, A.S., and J.C.H. Carter. 1974. Population dynamics of clado- cerans in Sunfish Lake, Ontario. Can. J. 2001. 52:1235-1242. Cole, G.A. 1953. Notes on copepod encystment. Ecology. 34:208-211. Cummins, K.W., R.R. Costa, R.E. Rowe, G.A. Moshiri, RsM. Scanlon and R.K. Zajdel. 1969. Ecological energetics of a natural population of the predaceous zooplankter Leptodora kindtii Focke (Cladocera). 'Oikos. 20:189-223. ' Deevey, E.S., Jr. 1942. Studies of the Connecticut Lake sediments. III. Biostratonomy of Linley Pond. Amer. J. Sci. 240:233-264. 313-33. 39 40 Duffy, W.G. 1975. The nearshore zooplankton of Lake Michigan adjacent to the Ludington Pumped-Storage Reservoir. Master's thesis. Michigan State University. 133 pp. Edmondson, W.T. 1957. Trophic relationship of the zooplankton. Trans. Am. Microsc. Soc. 76:225-245. Galbraith, M.G. 1967. Size selective predation on Daphnia by rainbow trout and yellow perch. Trans. Am. Fish. Soc. 96:1-10. Gannon, J.L. 1971. Two counting cells for enumeration of zooplankton micro-Crustacea. Trans. Am. Microsc. Soc. 90(4):486-490. Gliwicz, Z. 1969. Studies on the feeding of pelagic zooplankton in lakes with varying trophy. Ekol. Pol. A. 17:664-708. Hall, D.J. 1964. An experimental approach to the dynamics of a natural population of Daphnia galeata mendotae. Ecology. 45(1):94-110. Haney, J.F., and D.J. Hall. 1973. Sugar-coated Daphnia: a preserva- tion technique for Cladocera. Limnol. Oceanogr. 18:331-333. Harris, J.E. 1953. Physical factors involved in the vertical migration of plankton. Quart. J. Microscp. Sci. 94:537-550. Hutchinson, G.E. 1967. A Treatise on Limnology. Volume 11. John Wiley and Sons, Inc., New York. 1115 pp. Keen, R. 1973. A probabilistic approach to the dynamics of natural populations of the Chydoridae (Cladocera Crustacea). Ecology. 54:524-534. Kerfoot, W.G. 1977. Implications of copepod predation. Limnol. Oceanogr. 22(2):316-325. Kikuchi, K. 1930. Diurnal migration of plankton Crustacea. Quart. Rev. Biol. 5:189-206. Kwik, J.K., and J.C.H. Carter. 1975. Population dynamics of limnetic Cladocera in a beaver pond. J. Fish. Res. Bd. Can. 32:314-346. Lai, H.C., and J.C.H- Carter. 1970. Life cycles of Diaptomus oregonen- sis Lilleborg in Sunfish Lake. Can. J. Zool. 48:1299-1302. Marsh, C.D. 1897. On the limnetic Crustacea of Green Lake. Trans. Wis. Acad. Sci. Arts. Lett. 11:179-224. . 1903. The plankton of Winnebago and Green Lake. Bull. Wisconsin Geol. and Nat. Hist. Surv. 10:1-94. McLaren, I.A. 1963. Effects of temperature on growth of zooplankton, and the adaptive value of vertical migration. J. Fish. Res. Bd. Can. 20(3):685-737. 41 McNaught, D.C. 1966. Depth control by planktonic cladocerans in Lake Michigan. Proceedings of the 9th Conference of the Great Lakes Research, University of Michigan, Great Lakes Research Division, Pub. No. 15 pp. 96-108. McNaught, D.C., and A.D. Hasler. 1964. Rate of movement of populations of Daphnia in relation to changes in light intensity. J. Fish. Res. Ed. Can. 21:291-318. Moore, G.M. 1939. A limnological investigation of the microscopic benthic fauna of Douglas Lake, Michigan. Ecol. Monogr. 9:537-582. Noble, R.L. 1975. Growth of young yellow perch (Perca flavescens) in relation to zooplankton populations. Trans. Am. Fish. Soc. 104: 731-741. Nowak, V.K.E. 1975. The importance of zooplankton in the metabolism of lake. Archiv. Fuer. Hydrobiologie. 74:139-224. Patalas, J., and K. Patalas. 1966. The crustacean plankton communities in Polish lakes. Verh. Internat. Verein. Limnol. 16:432-440. Peterson, B.J., J. E. Hobbie, and J. Haney. 1978. Daphnia grazing on natural bacteria. Limnol. Oceanogr. 23:1039-1088. Plew, W.F., and R. W. Pennak. 1949. A seasonal investigation of the vertical movements of zooplankters in an Indiana lake. Ecology. 30:93-100. Prepas, E. 1978. Sugar-frosted Daphnia: An improved fixation techni- que for Cladocera. Limnol. Oceanogr. 23:557-559. Povich, M.A. 1978. A descriptive study of the zooplankton population of Lake Lansing. Master's thesis. Michigan State University. 33 pp. . Pennak, R.W. 1978. Fresh-water Invertebrates of the United States, Second Edition. John Wiley and Sons. New York. 803 pp. Siami, M. 1979. Distribution and abundance of benthic macro-inverte- brates in Lake Lansing. Master's thesis. Michigan State Univer- sity. 107 pp. Tappa, D.W. 1966. The dynamics of the associations of six limnetic species of Daphnia in Aziscoos Lake, Maine. Ecol. Monogr. 35:395- 423. Threlkeld, S.T. 1979. The midsummer dynamics of two Daphnia species in Wintergreen Lake, Michigan. Ecology(1):165-l79. Tonolli, V. 1958. Zooplankton swarms. Verh. Internat. Verein. Limnol. 13:776-777. 42 ward. H.B., and G.C. Whipple. 1959. Freshwater Biology. W.T. Edmond- son, ed. John Wiley and Sons, Inc., New York. 1248 pp. Wells, L. 1960. Seasonal abundance and vertical movements of planktonic Crustacea in Lake Michigan. U.S. Fish. Wildl. Serv. Fish Bull. 60:343-369. 1970. Effects of alewife predation on zooplankton popu- lations in Lake Michigan. Limnol. Oceanogr. 15(4):556-565. Wells, L., and A.M. Beeton. 1963. Food of the bloater, Coregonus hoyi, in Lake Michigan. Trans. Am. Fish. Soc. 92:245-255. 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Beaded—boon ‘60. no gain I-Iaodt«18« no hon]... .Oauqllia . vu‘ Cu‘lh 50 v... n«.o o .e.o .o.. .n..~ on.. a...” un.n ~«.n« «anus.- ..u... 3.0 a o a gamma .n.. ...n .~.~ u...” pm..~ -_mmmmmmmmm no.ou mg.“ e..n~ p... on.pa uuwuuuwmw «o.~. ...n 9..“ .e.- ~o.. o o o a... a a a o u... a... .~.~ o o oo.~ so.“ .~.o e .«.o o o o e a a a on." na.o a... .... on.» ...ou. .~.e« an.“ a... u..~n mummmmmwmw .... ~n.e .~.o .n.. .o.~u . uuunwu oo..o~ shrug e..~ .u..u a... e a a nu.. on.. .Axn aux. aux. pxuu .«xo. coca op.“ .nau ..«oo¢u . .3338. I. 3...... 51 Figure A-l. Structure of Daphnia. l. Daphnia galeata mendotae. Lateral view of adult female. 2. Postabdomen of Daphnia galeata mendotae. 3. Head of Daphnia galeata mendotae. 4. Daphnia retrocurva. Lateral View of adult female. 5. Head of Daph- nia retrocurva. 6. Postabdomen of Daphnia retrocurva. 52 53 Figure A—2. Structure of Bosmina and Chydorus. 1. Bosmina longirostris. Lateral view of adult female. 2. Postabdomen of Bosmina longirostris. 3. Chydorus sphaericus. Lateral View of adult female. 4. Postabdomen of Chydorus sphaericus. - . «a» '0'. U 0'” C Q 54 'n m. l u e A-B. 55 Structure of Geri da lacustris. Lateral v harpae. Lateral View of adult female. Acrcperus harpae. n 3 O 1 hnia and Acroperus. l. Ceriodaphnia ew of adult female. 2. Acroperus 3. Postabdomen of 56 .:fir * a» a?” I ..- ‘ .‘ 5%.... \s. ..-‘U -- O. ‘0‘ 0‘ \t i'r‘-" 0 oVuourM o\\. a .r.......- ..1 H0- 0‘ ‘WW‘|.¢H§~JPUUMH Vos. ...H» 57 Figure A—4. Structure of Sididae. l. Sida crystallina. Lateral View of adult female. 2. Diaphanosoma leuchtenbergianum. Lateral View of adult female. 58 o. '61MM' -.‘-‘_ .- - .... ‘. ‘ . v . "Ms. 7:33- 'W .. Ar ”$53 in “NJ. N, r ‘5’“:- “"‘{. I. I x1. ‘I‘ \\ . . . _ .‘q ‘ I ‘ . .. a“. ' 2": 7 ;- \n‘. : ' ".3 .- ‘é . ‘J I ,. IL .- 1' ‘ ‘ ‘ 59 Figure A—S. Structure of Cyclops bicuspidatus thomasi. l. Dorsal view of Cyclops bicuspidatus thomasi. 2. Fifth leg of Cyclops bicuspidatus thomasi. 3. Head of male Cyclops bicuspidatus thomasi. 60 \- C'VV‘ ‘0‘: II “ . ."'0 9.. xv .\ I" \ l ‘D I. , ‘ ’7 61 Figure A—6. Structure of Diaptomus oregonensis. 1. Lateral view of Diaptomus oregonensis. 2. Fifth legs of female Diaptomus oregonensis. 3. Fifth legs of male Diaptomus oregonensis. 62