Patterns of Invertebrate Size and Abundance in Aquatic Habitats

Abstract

The size distributions of invertebrate prey found in the vegetation, bare sediment, and open water habitats of a small, Michigan lake were quantified for the months of May through August, 1979. The distribution of prey body size in each habitat generally conformed to a lognormal distribution, allowing a simple characterization of prey size and abundance in each habitat. Seasonally, the abundance of large littoral invertebrates declined markedly, shifting the distribution of prey size in the vegetation and bare sediment habitats towards smaller prey. The total biomass of vegetation-dwelling prey (exclusive of gastropods) also declined dramatically from May to August. These seasonal changes in prey size and abundance were correlated with a reduction in foraging intake for the dominant fish species in the lake, the bluegill sunfish (Lepomis macrochirus). Bluegills whose diet was > 80% vegetation prey showed a > 3-fold decline in stomach contents (prey weight/fish weight) from May to Ausut, during which time prey biomass in the vegetation declined 2.5-fold.Key words: body size, lognormal distribution, benthos, foraging, Lepomis, Michigan