ANTHROPOGENIC INFLUENCE ON THE HEALTH OF OYSTER REEF ECOSYSTEMS IN SOUTHEASTERN NORTH CAROLINA AS EVIDENCED BY RANK-ORDER ABUNDANCE OF LIVING AND DEATH ASSEMBLAGES

Over the last half-century Crassostrea virginica oyster reef systems subjected to eutrophication and sedimentation have shown marked decline. Estuaries subjected to a high degree of anthropogenic eutrophication had poorer live-dead assemblage fidelity than those less impacted by human influence (Kidwell 2007). We examine the impact of long-term human influences such as sedimentation and eutrophication on the health of Crassostrea virginica oyster reefs located along the southeastern coast of North Carolina. We analyze the fidelity of the death assemblages to the living community in terms of rank order abundance and species richness, employing the methodology of Kidwell (2007). We hypothesize that increased nutrient deposition and accretion due to sedimentation from runoff has led to a significant change in rank order abundance of C. virginica and associated oyster reef fauna in these reefs. We also hypothesize that live-dead assemblage data will be more concordant in less disturbed environments than in environments with greater anthropogenic influence.

Live and dead assemblages were sampled from oyster reefs in five locations in New Hanover and Pender counties in southeastern North Carolina. All samples were gathered from environments not previously subjected to restoration efforts, shell plantings or recent commercial harvesting. Two sites at Masonboro Island are located within a currently protected area and are defined here as “less impacted.” Sites with greater anthropogenic influence were located on Hewletts, Pages, and Howe Creek. Three samples were taken within the oyster reefs at each site by excavating a 1m² area to 30 cm depth. Rank order abundance and species richness data were gathered from the living and death assemblages by identifying and counting specimens gathered from each site. Data collection has focused to date on samples from the uppermost centimeters of sediment at each site (>6100 specimens counted thus far). All samples are dominated by Crassostrea virginica, with minor amounts of Mercenaria, barnacles, Crepidula, and mussels, and no significant differences between live and death assemblages were observed in rank order abundance of taxa at any site. We anticipate that live and death assemblages will diverge in composition as samples from deeper within the substrate are examined.