Zooplankton assemblage and body size responses to severe lake eutrophication from agricultural activities near mink farms in Nova Scotia, Canada

Mink fur farming was once a widespread agricultural activity in southwestern Nova Scotia. Freshwaters near to and downstream of several mink fur farm operations have experienced severe water quality issues, including eutrophication and recurring algal blooms. Here, we use dated lake sediments to examine trends in primary producers and primary consumers from a hypereutrophic lake to assess how cladoceran assemblages have responded to extreme eutrophication. Shifts in the dominant pelagic cladoceran taxa began in the early 1900s, coinciding with an increase in sedimentary chlorophyll-a concentrations. Notably, small-bodied bosminids decreased, while taxa such as Chydorus brevilabris and Daphnia pulex spp. dominated assemblages in recent decades. Bottom-up ecological factors, such as decades of greater primary production, were the likely drivers of assemblage shifts of primary consumers. Consistent body sizes of bosminids throughout the sedimentary record suggested that pelagic cladocerans were not influenced solely by predation pressure from macroinvertebrates or fish. This study provides evidence of large-scale ecological shifts occurring at multiple trophic levels in a hypereutrophic temperate lake with mink farming operations in its catchment.