Benthic Communities as Mediators of Water Quality in Lower San Francisco Bay, California (2012-2019)

San Francisco Bay and Estuary is largely urbanized and developed, and the southern bay is the most urbanized with many sources of nutrients, many concerns that the system might become eutrophic, and many questions about how South Bay has maintained its relatively good health. The hypotheses for why South Bay is not eutrophic, where other bays have not been so fortunate, include high bivalve grazing that limits net phytoplankton growth and high turbidity which also limits the phytoplankton growth rate. Understanding the bivalve grazing rates in the south bay includes the necessity of understanding temporal and spatial distributions of bivalves. Despite the critical need to understand all controls on eutrophication, there are very few aquatic systems with good concurrent temporal and spatial data of bivalve grazing and phytoplankton biomass. Benthic communities, and especially bivalves, are critical in understanding water quality dynamics in aquatic systems, and therefore water availability for both human and ecological needs. As filter feeders, bivalves remove a large volume of organic and inorganic particles from pelagic habitats and consume and assimilate them into their tissues. In so doing, bivalves also produce and deposit organic rich feces and pseudofeces on the bottom where nutrients can be recycled. Through these processes, bivalves offer strong controls on nutrients, phytoplankton, suspended sediment, and contaminant dynamics. Bivalves are critical for nutrient translocation, storage, and transformation. The roles of bivalves in nutrient cycling are driven by many factors such as lifestyle (i.e., infaunal and epifaunal), habitat (e.g., river, intertidal zone), eutrophication, and hydrodynamics. Suspension feeding (i.e., biofiltration of the water column) and deposit feeding (i.e., sediment consumption) move nutrients from pelagic and benthic zones, respectively, into bivalves, where elements are assimilated or egested (Vaughn and others, 2018).