Effects of resuspension of eastern oyster Crassostrea virginica biodeposits on phytoplankton community structure

Abstract

Anthropogenic disturbances in the Chesapeake Bay (USA) have depleted eastern oysterCrassostrea virginicaabundance 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, we used 6 shear turbulence resuspension mesocosms (STURMs) 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 root mean square turbulent velocity of 1.08 cm s-1, energy dissipation rate of ~0.08 cm2s-3, and bottom shear stress of ~0.36-0.51 Pa during mixing-on periods during 4 wk of tidal resuspension. Phytoplankton increased their chlorophyllacontent in their cells in response to low light in tanks with biodeposits. The diatomSkeletonema costatumbloomed and had significantly longer chains in tanks without biodeposits. These tanks also had significantly lower concentrations of total suspended solids, zooplankton carbon, and nitrite +nitrate, and higher phytoplankton carbon concentrations. Results suggest that the absence of biodeposit resuspension initiates nitrogen uptake for diatom reproduction, increasing the cell densities ofS. costatum. The low abundance of the zooplankton population in non-biodeposit tanks suggests an inability of zooplankton to graze onS. costatumand negative effects ofS. costatumon zooplankton. A high abundance of the copepodAcartia tonsain biodeposit tanks may have reducedS. costatumchain length. Oyster biodeposit addition and resuspension efficiently transferred phytoplankton carbon to zooplankton carbon, thus supporting the food web in the estuary.