TAXON DIVERSITY AND COMMUNITY STRUCTURE OF FOSSIL MOLLUSCAN ASSEMBLAGES FROM THE MID-ATLANTIC CONTINENTAL SHELF (USA)

While fossil molluscan assemblages have been studied extensively along the U.S. Coastal Plain, relatively little is known about Holocene and Pleistocene molluscan assemblages on the mid-Atlantic continental shelf. As federal and state agencies explore the potential of mining sand offshore for beach nourishment, understanding the benthic communities inhabiting these areas and their variability across space and time is important. Vibracores collected by the Bureau of Ocean Energy Management (BOEM) and Delaware Geological Survey (DGS) from 2015-2017 allow us to assess changes in offshore molluscan taxon composition, diversity, and assemblage structure with respect to latitude, sediment type, and geologic age.

64 cores were drilled from offshore New Jersey, Delaware, Maryland, and Virginia, from water depths ranging from 6-15 m. Cores varied in length from 1-6 m, and were sampled for both mollusks and sediment grain size. Mollusks were sieved to 1 mm, identified to species level when possible, and counted to yield abundance data. Sediment type was categorized based on the Coastal and Marine Ecological Classification Standard (CMECS), then adjusted based on percentages of mud, sand, and gravel.

7000 specimens, representing 40 species of bivalves and gastropods, were documented in core samples. Analyses were limited to samples with greater than ten specimens, and taxa that occur in more than one sample. Initial results suggest that molluscan richness is somewhat higher along the Virginia Eastern shore than other regions in the mid-Atlantic. Richness and other diversity metrics displayed little to no relationship to sediment type. Non-metric multidimensional scaling (NMDS) reveals that molluscan species composition and abundance vary by both percentages of sand and mud as well as latitude.