BACKSCATTER MAPPING, FAUNAL SAMPLING AND BENTHIC HABITAT IN THE LONG ISLAND SOUND CABLE FUND SEAFLOOR HABITAT MAPPING PROJECT

Systematic studies of seafloor habitat are being conducted in Long Island Sound to understand sedimentary and biological processes and to inform the long-term management of this large water body which is shared by Connecticut and New York. Multibeam mapping provides high-resolution bathymetry and backscatter data sets for much of LIS, and SoMAS activities have focused on multibeam mapping in areas where full multibeam backscatter mapping data is not available, and in evaluating a faunal sampling strategy that is tied to backscatter. Using backscatter data to delineate areas of similar benthic communities has proven to be more effective than using morphological characteristics to delineate habitat in other settings near Long Island, and such an approach is likely to be important in characterize the nature and distribution of benthic habitats in LIS. Prior bathymetric multibeam data exists in some of the areas mapped by SoMAS and repeat mapping demonstrates that the seafloor is not stable in many areas where sand waves have different characteristics at different times, and at the mouth of the Connecticut River where a distinct seabed change was likely related to late-winter, early-spring peak river discharge. Repeat mapping can provide important insights into the stability of the seabed and the nature of the events that alter the bed. Sampling in three areas defined by backscatter demonstrates that replicate samples are needed to adequately characterize the benthic fauna. In particular, three replicate samples in a habitat, a value often used in benthic studies, would recover only 13-50% of the species present. Even at 10 replicate samples per habitat, under-sampling may recover only 60% of the species in a mud habitat.