Long-term patterns in Lake Champlain's zooplankton: 1992–2010

Abstract

We examined patterns in Lake Champlain zooplankton abundance from 1992 to 2010 using summer data from five study sites. Rotifer abundance (#/m3) for many common taxa such as Polyarthra, Kellicottia, and Keratella declined lakewide in the mid-1990s which coincided with the invasion of zebra mussels (Dreissena polymorpha) into Lake Champlain. The only rotifer to increase in density following zebra mussel invasion was Conochilus which is a colonial species. Long-term shifts in copepod and cladoceran community composition can be attributed to the arrival of another invasive species in 2004–2005, the alewife (Alosa pseudoharengus). Our results support previous findings that alewife predation can impact larger bodied zooplankton within temperate lake systems. Following alewife invasion into Lake Champlain, body length of Leptodiaptomus and Daphnia retrocurva decreased to a size at or below known alewife feeding preferences. In addition, smaller bodied copepods (primarily Diacyclops thomasi) have increased in abundance since alewife invasion while juvenile copepods have declined. Our results suggest that post-alewife zooplankton patterns are most likely due to alewife size-selective feeding strategies. Observed long-term changes in zooplankton community structure have potential implications for the lake's food web dynamics, particularly recent declines in large bodied zooplankton which may release smaller plankton from top-down control.