GEOGRAPHIC AND SUBSTRATE DISTRIBUTION OF HOLOCENE MOLLUSKS IN MID-ATLANTIC OFFSHORE DEPOSITS (U.S.A.)

While the paleoecology of Neogene mollusks has been studied throughout the U.S. Atlantic Coastal Plain, relatively little is known about the mollusks living on the continental shelf and how they are preserved in the Holocene record. The goal of this research is to: 1) map the geographic distribution of molluscan fauna from mid-Atlantic inner shelf environments and 2) determine how these communities vary according to substrate. Relationships between mollusks and the substrate in which they occur can help coastal managers target areas from which to draw sand for beach nourishment projects.

Forty-one vibracores were sampled from sites offshore of New Jersey, Delaware, Maryland, and Virginia, with core lengths ranging from 0-6.1m. Sampling methods for molluscan populations varied depending on density; large shells or fragments were sampled individually, while bulk samples were collected from shell beds with an interval of 0.045m, yielding a total of 311 samples. Taxon identification was based on apices, apertures, and ornamentation for gastropods and hinge structure and ornamentation for bivalves. Substrate was sampled once every 0.3m, at intervals of 0.045m, yielding 129 samples. Sediment samples were analyzed for grain size using a full set of half phi sieves.

Preliminary results suggest a high abundance of Mulinia and Spisula in the sampled vibracores. A few genera display substrate preferences, including Ensis, Cyclocardia, Gouldia, and Crepidula. Molluscan community structure appears to vary according to latitude and water depth. By studying the correlations between mollusks and the substrate they are found in, we can more effectively map potential sources of sand for beach nourishment.