Benthic fauna play a crucial role in estuaries by contributing to various ecosystem functions, including organic matter decomposition, water quality regulation, nutrient cycling, and serving as food source for higher trophic levels. Their biomass density varies from year to year, making it essential to understand this variability to assess how management actions and climate change may impact benthic invertebrates. However, there has been limited research on the interannual variability of benthic fauna biomass. To characterize and explain interannual variability in estuarine benthic biomass, our study examines species-specific biomass density data (ash-free dry weight per unit area) collected each summer from 1995 to 2022 by the Chesapeake Bay Program’s long-term Benthic Monitoring Program. The mean biomass density of benthic invertebrates in the Bay varies significantly from year to year, with a range of 4.3 to 14.6 g m^-2 (Figure 1). Bivalves, particularly Rangia cuneata, Corbicula fluminea, and Macoma balthica, dominate the mean biomass density and its interannual variability. To understand the drivers of this variability, we examined water quality data from the Chesapeake Bay Program (including temperature, salinity, dissolved oxygen, chlorophyll-a, total nitrogen, total phosphorous, and pH) and output from ROMS-ECB, a fully coupled, three-dimensional, hydrodynamic, and estuarine carbon biogeochemistry (ECB) implementation of the Regional Ocean Modeling System (ROMS). Preliminary results demonstrate correlations of important climate-associated and water chemistry variables with the benthic biomass data using generalized additive models. We hypothesize that year-to-year variations in streamflow and nitrogen loads influence eutrophication, which impacts hypoxia and consequently controls mean biomass density. Associating hypoxia with interannual variability in biomass can help improve our understanding of the different environmental factors that influence the abundance of benthic fauna in other estuaries worldwide and, hence, the impact of management and climate change on estuarine benthic fauna.

Figure 1: Mean macrofauna biomass density from all samples throughout the Chesapeake Bay from 1995 to 2022. Benthic samples were collected in the summer between July 15 and September 30.