The effect of clam grazing on phytoplankton spring blooms in the low-salinity zone of the San Francisco Estuary: A modelling approach

Outcomes of the CLAMFLOW model were to demonstrate how clams can indirectly impact phytoplankton growth through excretion of ammonium, and to illustrate how most published laboratory filtration rates are likely too high for application in the field. There are management implications from using too high a clam grazing rate in models that may overestimate their impact on trophic estuarine and wetland productivity. We suggest that improved prediction of bloom occurrences requires the use of lower filtration rates combined with observed clam abundances, and a suitable combination of flow and ammonium source concentrations. This simple modular model (CLAMFLOW) offers portability to other ecosystems and is designed to connect with estuary scale three-dimensional circulation or numerical biogeochemical models. Our model and results are applicable to other situations, including aquaculture development and bivalve restoration efforts, where the biogeochemical effects of bivalves on phytoplankton productivity need to be quantitatively understood.