This study evaluated the phytoplankton community and grazing influences of the zooplankton in oligotrophic Christine Lake, NH, by assessing the body size and clearance rates of the three dominant crustaceans: Sida crystallina (0.08 individuals L-1 ), Daphnia dubia (0.11 individuals L-1 ), and Leptodiaptomus sicilis (2.11 individuals L-1 ). Sida crystallina, typically a littoral cladoceran, was abundant throughout the water column in the open water, and contributed approximately 44% of the grazing in the pelagic zone. Phytoplankton abundance was examined to assess the potential impact S. crystallina might have on the phytoplankton in Christine lake. Aphanocapsa, the dominant phytoplankton in Christine Lake (relative abundance 68.54%), is a picocyanobacterium capable of forming colonies in the presence of planktonic grazers. Its ability to out-compete other phytoplankton due to differential grazing pressure suggests the appearance of the strong grazer S. crystallina may have contributed to the dominance of cyanobacteria in this oligotrophic lake.

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UNH Center for Freshwater Biology Research

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