MOLLUSCAN ASSEMBLAGES AS A PROXY FOR HOLOCENE PALEOENVIRONMENT: ASSESSING SPATIAL AND TEMPORAL SHIFTS IN SPECIES COMPOSITION AND COMMUNITY STRUCTURE IN THE CHESAPEAKE BAY

As ecological and economic pressures on the Chesapeake Bay intensify, understanding the natural and anthropogenic factors that have shaped the estuary becomes increasingly important for evaluating future restoration strategies. While previous studies have relied almost exclusively on microfossil data to reconstruct Holocene environments, molluscan assemblages can also provide information on major shifts in Bay habitats and benthic communities. This study sought to reconstruct the paleoenvironment of the Bay by assessing both temporal and spatial changes in molluscan assemblages. Shell samples were obtained from four piston cores (7.82 to 24.48 meters in length) collected in 1999 and 2003 from sites in the upper, middle, and lower Bay by the Marion-Dufresne. Both bulk samples and individual shells were collected from all fossiliferous core depths. Core materials were weighed and sieved to 0.5 mm, and molluscan specimens were sorted, identified, and counted. “Indicator species” with narrow temperature, salinity, and dissolved oxygen tolerances were identified from the literature and used to approximate environmental conditions. Species richness, abundance, evenness, and density were calculated at an array of taxonomic levels. Information on Bay microfossil assemblages and AMS radiocarbon dates was provided by U.S. Geologic Survey collaborators to aid in spatial correlation and temporal reconstruction of the cores. Finally, rarefaction analysis was used to determine effects of sampling on species richness. Preliminary results suggest that some of the environmental shifts documented in the microfossil assemblages coincide with changes in molluscan species composition and richness.