The Vernal And Summer Zooplankton In Surface Waters From A Small Cove In Stockton Reservoir


Rick Casey

Date of Graduation

Spring 1977


Master of Science in Biology



Committee Chair

Milton Topping


Zooplankton collections were made at three sites in the Little Sac arm of Stockton Reservoir, Missouri, from May 11, 1975 until July 19, 1975 and from ten sites along the entire Little Sac arm on June 10, 1976. A total of 12 species of zooplankton were collected. Diurnal, seasonal, and among site variation in total numbers and individual species density were generally large with greatest densities observed during night in shallow water. The zooplankton underwent striking numerical changes with both the cladocera and copepod populations becoming less abundant from May to July. Some of the change may have been due to predation by larval fish. During 1975, zooplankton were most dense during May when larval fish were uncommon and were least dense in July when larval fish were most abundant. Although their correlation is not significant, fewer zooplankton were collected where fishes were the most abundant on June 10, 1976. Peak densities of Diaptomas siciloides, Cyclops bicuspidatus thomasi, Mesocyclops edax, Diaphanosoma leuchtenbergianum, and Daphnia parvula were temporally separated and the largest individuals of these species were collected after dark, indicating either heavy predation in the daytime or vertical migration of the larger animals. The average sizes of zooplankton were not significantly correlated with the abundance of larval fish either during 1975 or in 1976. Decrease in birth rate of D. siciloides suggests that food availability may account for some of the differences in its density. Temperature appeared to be important in determining the density of zooplankton.

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© Rick Casey