Grazing Impacts of Rotifer Zooplankton in a Seasonally Cyanobacteria-Dominated Lake

Primary author: Kathryn Sweeney
Co-author(s): Gretchen Rollwagen-Bollens
Faculty sponsor: Dr. Gretchen Rollwagen-Bollens

Primary college/unit: Arts and Sciences
Campus: Vancouver


Vancouver Lake in western Washington is one of many lakes characterized by annual and often toxic cyanobacteria (harmful algae) blooms. Phytoplankton and cyanobacteria are the primary producers of lake systems, and the foundation on which zooplankton grazers, like copepods or rotifers, are able to survive. Thus, toxic blooms may be controlled top-down by these micrograzers, which is information relevant to resource managers and the public alike. Previous studies have shown copepod grazing to influence bloom formation, and bloom decline to be driven in part by microzooplankton community grazing. However, we don’t understand the individual roles of particular micrograzers such as rotifers. To address the role of rotifers, we are conducting feeding incubations with water collected from Vancouver Lake. Preliminary results show that rotifers have a mild grazing effect on phytoplankton and cyanobacteria only after the peak of a bloom, while the whole microzooplankton community has a large impact both before and after the peak. This seems to suggest that other non-rotifer microzooplankton such as ciliates or dinoflagellates may be responsible for the majority of bloom suppression in both spring and fall. Further microscopical analysis of samples will elucidate which plankton species were present in the lake during each experiment, and which phytoplankton taxa rotifers had been preferentially feeding on. Additionally, due to an unexpected shift in the timing of the 2019 bloom cycle, supplemental experiments will be performed during spring 2020 to complete our understanding of seasonal dynamics related to cyanobacteria blooms.