MOLLUSCAN PALEOECOLOGY AND SUBSTRATE AFFINITIES ON THE MID-ATLANTIC CONTINENTAL SHELF

While the fossil record of marine mollusks has been examined in detail along the U.S. Atlantic Coastal Plain, less is known about the modern mollusks living in sandy inner shelf environments and how their remains are incorporated into the sedimentary record. This research is part of a larger study supported by the Bureau of Ocean Energy Management (BOEM) and the Delaware Geologic Survey (DGS). The goals of this multi-year study include: (1) examining the paleoecology of molluscan communities across space and time, (2) developing an amino acid racemization chronostratigraphic framework for these deposits, (3) determining the extent of time averaging in molluscan assemblages, and (4) tracking paleoecological changes resulting from environmental and anthropogenic shifts assemblages through time. Here, we present preliminary results for the first goal, focusing on quantifying molluscan taxon composition, richness, diversity, evenness, and community structure.

Twenty-six vibracores were drilled off the coast of New Jersey, Delaware, Maryland, and Virginia over the past two years. Cores were 10cm in diameter, 1-6m long, and sampled water depths from 6-15m (above extreme storm wave base). Cores were picked for mollusks and the sediment was sieved into grain size fractions. Mollusks were sieved to 1mm, identified to the genus level, and counted to yield abundance data. This preliminary survey included 164 samples, representing an average of 7 sample depths per core.

The molluscan community recorded in these cores is relatively low in richness and abundance. In total, 3000 specimens, representing 24 species of bivalves and gastropods were documented. The number of individuals per sample ranged from 1-140 (x̅ = 18), with species richness per sample ranging from 1-11 (x̅ = 3.6). The most common genera sampled included Mulinia and Spisula, which numbered in the hundreds. Shannon diversity remained relatively low (range 0-1.7; x̅ = 0.71) across samples, although evenness (Buzas-Gibson's E) varied widely (range 0.15 – 1; x̅ = 0.71). Non-metric multi-dimensional scaling revealed clustering based on geographic region, a pattern driven in part by latitude. Sedimentology in core samples varied little, yet a handful of genera demonstrated specific substrate preferences including Ensis, Gouldia, and Crepidula.