ONSHORE-OFFSHORE TRENDS IN MARINE MACROBENTHIC COMMUNITIES IN THE PRESENCE OF ANTHROPOGENIC IMPACTS

Quantitative analyses of living communities comprise an important research direction in Paleobiology and can aid ecologists in establishing baselines, and determining human impacts in modern ecosystems. Changes in diversity resulting from physical and environmental factors associated with increasing depth have been documented in a variety of habitats. Using coastal and shallow subtidal habitats of the Outer Banks (North Carolina, USA), this study is aimed at assessing spatial variability in diversity and abundance of benthic marine invertebrates (macrofauna), with respect to relative anthropogenic effects.

Preliminary data are based on 75 dredge samples of live benthic marine invertebrates from a variety of coastal habitats. Samples from 28 localities have yielded over 2,800 live individuals representing 135 species from 116 genera, and 8 phyla (Annelida, Arthropoda, Brachiopoda, Bryozoa, Cnidaria, Echinodermata, Mollusca, and Porifera). Quantitative analyses of samples along a depth gradient (13 to 63 m) suggest a surprising stability in alpha diversity across multiple habitats and faunal associations. The limited variability in diversity relative to water depth may be the result of anthropogenic effects which, by affecting primarily nearshore habitats, may have preferentially altered the alpha diversity of shallow-water sites. The sites sampled so far also include a transect parallel to shore, consisting of a series of localities within, and adjacent to, a habitually dredged harbor channel. Diversity within the harbor channel is low and increases away from the channel in both directions. This pattern is consistent with the explanation that human impacts may result in suppressed diversity, although interpretations based on a single transect are tenuous.

These preliminary analyses suggest that human impacts may play a significant role in affecting alpha diversity of local benthic marine invertebrate communities in the study area. Further sampling efforts should allow us to assess the validity of these tentative conclusions. Ultimately, these data should serve to facilitate evaluations of whether diversity metrics respond predictably to anthropogenic effects in the region and to determine if marine benthos can serve locally as an effective measure of the relative intensity of human impacts.