Benthic Community and Bivalve Metrics Data in the Sacramento - San Joaquin Delta from 2015 to 2018

Declining phytoplankton biomass and the resulting stress on the food web has been suggested as one contributor to the decline of Delta Smelt and other fish species in the San Francisco Bay (SFB) and the Sacramento San Joaquin River Delta. Filter feeding by two species of bivalves, Corbicula fluminea and Potamocorbula amurensis, has been shown to control phytoplankton growth rate in the SFB and Delta and both are thought to be partially responsible for the reduction in food for pelagic species. Phytoplankton growth rate is dependent on spatially and temporally varying nutrient concentrations, light availability, transport time, and pelagic and benthic grazing losses. Bivalve grazing has the potential to limit primary production at phytoplankton source locations and to limit effective connectivity of habitats by grazing in the conduits that connect different habitats. It is important to determine the factors that control the success of each species of bivalve if we are to understand when and where the pelagic food web is most affected by bivalve grazing. Therefore, we need to protect, build, or restore habitat that is likely to produce phytoplankton for local consumption and export. Benthic communities are a good monitor of acutely and chronically stressful environments because they are stationary, accumulate contaminants, and respond to low and high phytoplankton biomass. Changes in the benthic community structure occur normally, and benthic species distributions are dependent on the physical habitat (substrate and depth), physiological limits, and predators. Therefore, seasonal and interannual differences in freshwater flow result in both seasonal and episodic changes in species abundance and community composition. The Sacramento Watershed has experienced below normal rainfall and dry conditions with sporadic wet years for the past decade. However, heavy rainfall in water year 2017 (October 2016 to September 2017) ended a five-year drought and set the record for California's wettest year since 1983. The severity and duration of a potential change in the benthic community as a result of this increase in freshwater is still unknown, yet it is unlikely for such a drastic change in salinity as this to go unnoticed.