A spatially and temporally intensive sampling study of benthic community and bivalve metrics in the Sacramento-San Joaquin Delta, 2007-18

Phytoplankton is an important and limiting food source in the Sacramento-San Joaquin Delta and San Francisco Bay; the decline of phytoplankton biomass is one possible factor in the pelagic organism decline and specifically in the decline of the protected delta smelt. The bivalves Corbicula fluminea and Potamocorbula amurensis (hereafter Corbicula and Potamocorbula, respectively) have been shown to control phytoplankton biomass in several locations throughout the system, and their distribution and population dynamics are therefore of great interest. As one element of the Department of Water Resources' (DWR) and the Bureau of Reclamation's (BOR) Environmental Monitoring Program (EMP), the Generalized Random Tessellation Stratified (GRTS) program examines the spatial and temporal extent of both Corbicula and Potamocorbula control on phytoplankton. The GRTS benthic monitoring program is one element of DWR's and BOR's EMP wherein the impact of water project operations on the estuary are determined. These impacts are determined by changes in benthic fauna presence, abundance and distribution of the benthos associated with physical factors in the estuary, and the detection of newly introduced species in the estuary. DWR expanded their benthic monitoring program to include spatially intensive sampling (GRTS) in spring and fall of every year beginning in 2007. The GRTS program samples 175 benthic stations (fifty stations that are monitored every year and 125 randomly selected new stations that are changed yearly) throughout the Delta and northern San Francisco Bay in one week in May and October.