LIVE-DEAD AGREEMENT OF MOLLUSCAN COMMUNITIES ALONG AN EUTROPHICATION GRADIENT

Eutrophication has been identified as the most pressing environmental problem facing Long Island Sound (LIS) and has been shown to adversely affect live-dead agreement of molluscan communities, as measured by comparing taxonomic similarity using the Jaccard-Chao Index and the congruence of rank order abundance using the Spearman rho value. Despite predicted taphonomic processes, live-dead agreement is frequently high in marine settings except in areas of heavy anthropogenic influence where the death assemblage represents a time averaged mix of individuals including those which inhabited the locality prior to human disturbance. In order to evaluate the effects of long-term eutrophication on the molluscan community in LIS and the sensitivity of the method to varying levels of well documented anthropogenic impact, five live-dead censuses were conducted capturing the entirety of the eutrophication gradient of LIS. Eutrophication increases with human population density as one travels LIS west towards New York City and decreases as one nears the influence of the open ocean towards Rhode Island. Preliminary results from the three central localities along the Connecticut coast (from west to east: Greenwich, Westport, and Stratford) show that the Stratford site has the highest live-dead agreement of the three sites both in rank-order abundance and taxonomic similarity, confirming expectations that sites farthest east will be the least affected by eutrophication. The Greenwich site shows the lowest rank-order correlation, consistent with its position at the west end of LIS, but shows only a slight decrease in taxonomic similarity, while the centrally located Westport site shows the most substantial decrease in taxonomic similarity. Ongoing work will include live-dead censuses in the far eastern (New London, CT) and western (New Rochelle, NY) portions of LIS. While these preliminary results suggest that rank-order may provide a more sensitive measure of anthropogenic impact, the combination of these metrics offer a means of establishing a crucial pre-anthropogenic ecological baseline with which to evaluate current conditions and restoration efforts. High levels of taxonomic similarity and rank abundance in low impact localities lend further support to the use of death assemblages in ecologic studies.