ZOOPLANKTON ASSEMBLAGE RESPONSES TO DISTURBANCE GRADIENTS

Zooplankton assemblages of 19 New England lakes were evaluated in relation to lake trophic state, riparian land use, fish assemblage features, and physicochemical factors for potential food web indicators of lake ecosystem condition or health. Principal component analysis (PCA) of species abundance data contrasted productive warmwater lakes dominated by rotifers, small cladocerans, and cyclopoid copepods and nauplii with cold-water salmonid systems dominated by calanoid copepods and large cladocerans, and with few rotifers. The use of 12 aggregate zooplankton assemblage variables based on taxonomic group, body size, life-history stage, and feeding guilds improved the amount of the explained cumulative variance (63.2%) over species data (40.3%) in the first two axes of the ordination. In a second PCA the environmental variables were constrained with respect to the zooplankton variables. This analysis identified total phosphorus, chlorophyll a, cold-water fish assemblages, number of introduced fish species, piscivore numbers, and the percentage of disturbed shoreline as dominant gradients. Small-bodied assemblages represented by small cladocerans, rotifers, ostracods, nauplii, and cyclopoid copepodites were associated with the most disturbed systems. The pattern of distribution among large- and small-bodied taxa from the PCA was used to formulate metrics which were then correlated to the gradients.