Variation in the Biomass of Functional Groups Comprising the Open-water Plankton of Shallow Lakes in Ireland

The open-water plankton form a complex food web that is crucial to the cycling of nutrients through the ecosystem. This food web consists of two interconnected loops: the classical grazer loop and the microbial loop. Here, we describe in detail the seasonal composition and biomass of the planktonic food web of six Irish shallow lakes. The lakes were sampled three times in 2000, and the biomass of zooplankton, phytoplankton, ciliates, flagellates and bacteria was measured. Total biomass ranged from 0.08mg C ml 1 to 1.47mg C ml , and a significant portion of the biomass comprised microbial elements. Zooplankton biomass was generally highest in April, corresponding with large amounts of Daphnia . With the exception of zooplankton, all other group biomasses were correlated with physicochemical parameters indicative of nutrient status.