Microzooplankton Grazing in Green Water—Results from Two Contrasting Estuaries

We measured seasonal variations in microzooplankton grazing in Long Island Sound (LIS) and San Francisco Bay (SFB). There was consistent evidence of nutrient limitation in LIS, but not SFB. We found higher chlorophyll a concentrations in LIS compared with SFB. In spite of differences in phytoplankton, there were no differences in microzooplankton abundance (summer: LIS, 12.4±1.8×10 indiv.L; SFB, 14.1±3.0×10 indiv. L), biomass (summer: LIS, 30.4±5.0 μgCL; SFB, 26.3± 5.9 μgCL), or grazing rates (summer: LIS, 0.66± 0.19 day; SFB, 0.65±0.18 day) between the two estuaries. In common with many other investigators, we found many instances of saturated as well as insignificant grazing. We suggest that saturation in some cases may result from high particle loads in turbid estuarine systems and that insignificant grazing may result from extreme saturation of the grazing response due to the need to process non-food particles.