ANTHROPOGENIC INFLUENCE ON THE RANK-ORDER ABUNDANCE OF LIVING AND DEATH ASSEMBLAGES OF SEA GRASS ASSOCIATED MOLLUSKS AT CHADWICK BAY, ONSLOW COUNTY, NC

Ecosystems are constantly undergoing changes due to human influences. High input of nutrients, changes in salinity, dredging and drilling, boat traffic, runoff, and clamming are examples of factors that degrade water quality, causing loss of habitat (Kidwell 2007). Such disturbances have both indirect and direct effects on sea grass ecosystems, causing habitat fragmentation (Bell et al. 2002) and influencing communities that live in them. Changes in growth rate and survival may cause discordance between the local living community of mollusks and the dead assemblages in taxonomic composition (Hubt & Nuttle 2007). Because sea grass habitats in Chadwick Bay, Onslow Co., North Carolina, have been disturbed by these factors, we hypothesize that living and death assemblages of the molluscan community will show discordance in taxon rank-order abundance and diversity due to anthropogenic influence.

To test this hypothesis, samples of live-dead mollusk assemblages were taken from four different transects within Chadwick Bay. Each transect was divided into three 5m² sampling areas, distributed from 20 meters to 100 meters from the Intracoastal Waterway. The upper 30 cm of sediment was sampled using 25 randomly located hand cores within each sampling area. Mollusks were extracted using a 2-mm sieve. Following Kidwell's approach, this research was based on a minimum of 20 live and 20 dead specimens per sample (the minimum number of specimens needed to compare rank-order abundance between live and death assemblages using Spearman's rho). These data were collected to obtain a baseline for measuring the impact of disturbance and see if there is fidelity in taxonomic composition between the live and death assemblages. Preliminary results indicate that the death assemblages are far more diverse than the living assemblages, although a few taxa (particularly Solemya, an organic-loving species found in areas of anthropogenic eutrophication; Kidwell 2008) are found only in the live assemblages. Two samples for which analyses are complete (Transect 3, samples B and C) yielded total diversities of 28 and 26 genera and Spearman's rank correlation of 0.2453 and 0.3390, both nonsignificant. This discordance in rank ordering between live and dead assemblages supports our hypothesis of significant anthropogenic impact in this area.