ZOOPLANKTON POPULATION ANALYSIS AND BODY LENGTH MEASUREMENT IN DAMARISCOTTA LAKE, MAINE IN RELATION TO ALEWIFE POPULATIONS

The purpose of the study was to analyze the impact of predation from juvenile alewives (Alosa…) on zooplankton population numbers and overall body size, to determine if predation primarily affects the larger-bodied zooplankton groups, driving down their populations and allowing other groups to flourish. Zooplankton groups in Damariscotta Lake, Maine, collected on 5 monthly sampling dates (June to October 2008) and identified, counted, and measured for body length. Eight zooplankton groups were identified and measured: Cyclopoida, Calanoida, Daphniidae, Bosmina, copepod nauplii, Asplanchnidae, Conochilus, and Holopedium spp.

All zooplankton groups changed in abundance over the duration of the study period. Daphniidae in particular were affected by alewife predation; initially abundant, their populations dropped dramatically soon after the appearance of alewife juveniles. Average body length also dropped somewhat over the five month span. Copepod nauplii had a large population increase, as well as a small increase in average body size. Interestingly, zooplankton dynamics in Damariscotta Lake variety by lake basin, with zooplankton consistently more abundant and larger in the main (north) basin than in the Muscongus basin (south).

Changes in zooplankton abundance and length correspond to the time of the summer that juvenile alewives would be expected to consime larger zooplankton. Difference between basin maybe related to basin morphology, differential usage by juvenile alewives, or productivity.