USING BENTHIC MARINE INVERTEBRATE COMMUNITY ASSEMBLAGES AS PALEO-BATHYMETRYIC PROXIES: A DIRECT TEST FROM RECENT COASTAL ECOSYSTEMS OF NORTH CAROLINA USING MULTIVARIATE ORDINATIONS

Changes in environment associated with increasing water depth such as temperature, salinity, and nutrients should result in fundamental differences in community composition. Whether depth and its related environmental parameters control faunal composition has, however, not been directly tested. Furthermore, paleontological studies are often restricted to a few higher taxa or heavily biomineralized organisms, potentially impeding the ability of ordination techniques to accurately detect ecological gradients. If depth is a widespread primary control on community structure, and can be readily inferred from paleontological data, this would have significance for stratigraphic patters of fossil occurrences.

We evaluated modern macro-faunal associations of marine invertebrates along an onshore-offshore gradient in North Carolina to determine the relationship between community composition and bathymetry, compare the performance of various ordination techniques, and to evaluate whether differences in resolution between modern and paleontological data reduce the ability of ordinations to effectively capture ecological gradients. Axis 1 scores correlate with actual depth values of species and samples, confirming that communities ordinate along an axis that primarily reflects bathymetry and its environmental correlatives, producing analogous results with DCA, NMDS, CA, and PCO. Axis 1 scores also correlated significantly with depth for ordinations restricted to heavily biomineralized taxa, as did those excluding mollusks. Ordinations using only mollusk did not perform as well, however, limiting the analysis to robust mollusks improved the clarity of the bathymetric signal.

Some types of paleontological data should, therefore, accurately captured bathymetric gradients, and in coastal ecosystems of North Carolina, bathymetry appears to be a primary controlling factor. Although it is arguable that individual case studies such as this one can support broader generalizations, these results are promising and consistent with multiple paleontological studies. Fossil communities may provide robust quantitative estimates of bathymetry with potential applications to paleoecology and stratigraphy.