Zooplankton influences on phytoplankton, water clarity, and nutrients in Lake Tahoe
2021
Bess, Zachary | Chandra, Sudeep | Suenaga, Erin | Kelson, Suzanne | Heyvaert, Alan
The grazing effects of zooplankton communities are predicted to be strongest in mesotrophic lakes relative to eutrophic and oligotrophic lakes, an idea known as the Mesotrophic Maximum Hypothesis. We tested if the predictions of this hypothesis depend on the community of zooplankton present by evaluating whether the community of zooplankton, in addition to lake trophic state, interact to determine the magnitude of grazing effects. We conducted mesocosm experiments to evaluate the effects of Daphnia spp., Epischura nevadensis, and juvenile and adult Mysis diluviana on ecosystem function in oligotrophic Lake Tahoe and its more productive embayment, Emerald Bay. In the Lake Tahoe experiment, the Daphnia and the Adult Mysid treatments produced lower dissolved organic carbon concentrations, and the Epischura treatment yielded lower soluble reactive phosphorus concentrations compared to a Control treatment that lacked macrozooplankton. In the Emerald Bay experiment, the Daphnia treatment lowered chlorophyll a concentrations, the Daphnia and Juvenile Mysid treatments reduced small particle (diameter 0.5 – < 5 µm) concentrations, and each of the species treatments produced higher ammonium concentrations and DIN/SRP ratios compared to the Control. Analyses of similarities (ANOSIM) indicated that these taxa differed from one another in their overall effects on Emerald Bay water, but not on Lake Tahoe water. This finding supports the Mesotrophic Maximum Hypothesis, but also shows that grazing effects are dependent on the taxonomic makeup of the zooplankton community in addition to lake trophic state. As ongoing cultural eutrophication continues to elevate Lake Tahoe's productivity, the roles and importance of the lake’s zooplankton taxa may diverge.
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