THE BENTHIC GEOLOGIC HABITATS OF LONG ISLAND SOUND IN THE VICINITY OF THE THIMBLE ISLANDS AND BRANFORD RIVER, CONNECTICUT, USA

Using side-scan sonar, surface sediment grab samples, underwater video imagery and digital orthophotographs, 4 km2 of benthic geologic habitats were mapped in north-central Long Island Sound offshore of Branford, Connecticut, U.S.A. Units were classified using a naming convention that is based on the geologic processes, morphologic form (separated into two different environment groups (bayfloor versus marginal habitats)), particle size, biota and anthropogenic impacts. This naming scheme is flexible and can be adapted to other areas, and allows scientists, managers and the general public to understand the classification method used. The distribution of geologic habitats in the study site are complex but generally, coarser units (sand, limited amounts of gravel and abundant gravel sized shell fragments) are found near bedrock outcrops, forming an erosional terrace as fine-grained material (silt and clay) is removed by wave action. Aerally the largest units are low-energy depositional habitats, which range in water-depth from subtidal flats <1.5 to >10 m in incised channels and are significant sinks for fine-grained sediment (sandy silt, silt and clayey silt). The fine-grained sediment currently present in the Long Island Sound basin are likely from several key sources: 1. Erosion and transport of silt and clay glacial lakefloor deposits (varves) deposited during the Late Wisconsinan. 2. Sediment transported down the major rivers draining into the Long Island Sound basin during large storm events. 3. Fine-grained organic sediment, which accounted for <4 % of the fine-grained sediment, and is largely a product of the decay of macroalgae, particularly in the northern coves.