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Impact of eastern oyster Crassostrea virginica biodeposit resuspension on phytoplankton community structure in estuarine systems with tidal resuspension

Elka T. Porter*, Eric Robins, Sarah Davis, Richard Lacouture, Jeffrey C. Cornwell

*Corresponding author:

ABSTRACT: Anthropogenic disturbances in the Chesapeake Bay have depleted Eastern oyster Crassostrea virginica abundance and altered the estuary’s environment and water quality. Efforts to rehabilitate oyster populations are underway, however, the effect of oyster biodeposits on water quality and plankton community structure are not clear. In July 2017, six shear turbulence resuspension mesocosms (STURM) were used to determine differences in plankton composition with and without the daily addition of oyster biodeposits to a muddy sediment bottom. STURM systems had a volume-weighted RMS turbulent velocity of 1.08 cm s-1, energy dissipation rate ~0.08 cm2 s-3 and bottom shear stress ~0.36–0.51 Pa during mixing-on periods during four weeks of tidal resuspension. Phytoplankton increased their Chl a content in their cells in response to low light in tanks with biodeposits. The diatom Skeletonema costatum bloomed and had significantly longer chains in tanks without biodeposits. These tanks also had significantly lower total suspended solids concentrations, zooplankton carbon concentrations, nitrite+nitrate concentrations, and higher phytoplankton carbon concentrations. Results suggest that the absence of biodeposit resuspension initiates nitrogen uptake for diatom reproduction, increasing the cell densities of S. costatum. The low abundance of the zooplankton population in non-biodeposit tanks suggests an inability of zooplankton to graze on S. costatum and negative effects of S. costatum on zooplankton. A high abundance of the copepod Acartia tonsa in biodeposit tanks may have reduced S. costatum chain length. Oyster biodeposit addition and resuspension efficiently transferred phytoplankton carbon to zooplankton carbon, thus supporting the food web in the estuary.