Zooplankton Abundance, Biomass, and Size-Distribution in Selected Midwestern Waterbodies and Relation with Trophic State

Abstract

ABSTRACT Zooplankton abundance and biomass were measured in natural lakes and impoundments in Iowa, Kansas, Missouri, and Oklahoma during summer. Zooplankton exhibited wide ranges of abundance (70,000-1,000,000 individuals/m3) and biomass (45–1,000 mg/m3). Communities were dominated by rotifers; they comprised 70% or more of the zooplankton abundance in 41 lakes and, on average, comprised 53% of zooplankton biomass. Zooplankton in Missouri were significantly smaller than those collected in me other states, suggesting predation and regulation of size structure by zooplanktivorous fish may have differed among states at the time of this study. Within the data set, neither the microzooplankton nor the component groups of the macrozooplankton showed consistent changes witii lake trophy. Among die Missouri reservoirs, Daphnia sp. decreased and Diaphanosoma sp. increased in relation to algal chlorophyll. Both zooplankton abundance and biomass were positively correlated with algal chlorophyll (r=0.30–0.58). This finding is consistent with general zooplankton-lake productivity relations, and correlations improved when our data were combined with literature values (r= 0.73 and 0.78) to encompass a broad trophic state and geographic range.