Impact of Eastern oyster Crassostrea virginica biodeposit resuspension on the seston, nutrient, phytoplankton, and zooplankton dynamics: a mesocosm experiment

To test the effect of Crassostrea virginica biodeposit resuspension on nutrient and plankton dynamics, a 4 wk experiment was performed in six 1000 l shear-turbulence-resuspension-mesocosms (STURM) without a sediment bottom (R). Three tanks (R_BD) received daily additions of oyster biodeposits (5.77 +/- 3.33 mg total suspended solids). Simulated tidal resuspension of bio-deposits in the R_BD tanks resulted in concentrations of 90 mg l(-1) total suspended solids when mixing was on, decreasing to ca. 20 mg l(-1) when mixing was off. However, bulk settling speeds of particles in the R_BD tanks increased 3-fold over the experiment. Particulate nitrogen, phosphorus, and carbon concentrations as well as dissolved inorganic nitrogen, nitrate + nitrite, dissolved organic phosphorus, and total dissolved phosphorus levels were significantly higher in the R_BD tanks. In the R_BD tanks the greatest part (72%) of the nitrogen was partitioned in the total dissolved nitrogen, but in the R tanks the greatest part (51.5%) was partitioned in microphytobenthos. While chlorophyll a concentrations were higher in the R_BD tanks than in the R tanks (despite tunicates being found in the R_BD tanks), phytoplankton biomass (carbon) as estimated using direct cell counts was not significantly different and there was little difference in phytoplankton composition. However, the ratio of chl a:C was higher in the R_BD tanks, suggesting phytoplankton adjusted to low light in the R_BD tanks by increasing chl a in their cells. Acartia sp. abundance was also raised in the R_BD tanks. Addition and regular tidal resuspension of oyster biodeposits profoundly affected nutrient dynamics, nitrogen partitioning, and zooplankton community dynamics.