CHARACTER AND ECOLOGIC IMPORTANCE OF SHELL BEDS FLANKING CAPE-ASSOCIATED SHOALS IN SOUTHEASTERN LONG ISLAND SOUND

The shell bed observed along the lower flanks of a cape-associated shoal off Herod Point on Long Island, NY, is a product of high molluscan productivity atop the shoal, strong oscillating tidal currents that winnow the shells from the terrigenous sediment, and shoal morphology. These processes are active and shell accumulation is ongoing. The bed is continuous, narrow, and wedge-shaped in cross-section. It has a densely packed, clast-supported fabric composed largely of un-degraded surfclam valves. It is widest (approximately 40 m) along the central part of the western flank of the shoal where gradients are steep and a stronger flood tide results in residual flow. It is narrower and thinner toward the landward extents of the shoal where currents are too weak to transport larger valves and gradients are less steep, limiting bedload transport mechanisms by which the shells are concentrated. Reconnaissance mapping off Roanoke Point, which lies 12 km to the east, suggests that shell beds are also present at the other cape-associated shoals off northeastern Long Island where relatively similar geomorphic and oceanographic conditions persist. These shell beds are ecologically important because they form benthic habitats with rough, hard substrates on the Long Island Sound seafloor at the boundary between the muddy basin floor and the mobile sand of the shoals. Bottom photography shows that crabs construct burrows in the shell deposits, starfish graze on its surface, juvenile finfish shelter between the shells, and sessile fauna and flora attach themselves to the hard substrate provided by shells. These data demonstrate that the shell deposits add considerably to the overall benthic compositional complexity of the Sound. This complexity increases seafloor habitat diversity and likely affects the distribution and dynamics of faunal populations and characteristics of benthic communities.