DID THE PLIO-PLEISTOCENE EXTINCTION AFFECT THE TROPHIC ECOLOGY OF NORTH CAROLINA MOLLUSCS?

The nature, extent, and timing of the multi-phased Plio-Pleistocene extinction of molluscs, widely recognized elsewhere in the western Atlantic, are poorly understood for the Carolinas. As part of a three year Research Experiences for Undergraduates study, we compared molluscan trophic ecology for the Duplin Formation (prior to the extinction), the lower James City and Waccamaw formations (following an initial turnover pulse), and the upper James City and Waccamaw formations (following a second turnover pulse). Previous REU work focused on more northerly sites near the Neuse River; in 2010 we added Duplin and lower Waccamaw sites in southeast North Carolina. New sites include the Pliocene Duplin Fm (Robeson Farm near Tar Heel, NC) and the Pleistocene lower Waccamaw Fm at Acme, NC, Neils Eddy Landing on the Cape Fear River near Acme, and Holloman Pit in Whiteville, NC (>1,500 gastropods and >16,000 bivalves). Bulk samples were sieved through ¼” mesh and specimens picked, sorted and identified to genus; life modes were assigned using the NMITA molluscan life modes database.

Data from the new localities confirm previous results (Kelley et al. 2009, Dietl et al. 2010) that most measures of trophic structure did not change significantly across the extinctions. Percent suspension feeding bivalves was consistent among three Duplin sites (73-76% of genera, 94-99% of individuals). Five lower Waccamaw sites, including the three new sites, yielded 73-79% suspension feeding bivalve genera. Suspension feeders made up 92-99% of bivalve individuals for all but the Holloman site (79%, significantly less than for other Duplin and Waccamaw sites). For all localities combined, suspension feeders were 75%, 76%, and 72% of Duplin, lower and upper Waccamaw bivalve genera respectively (97%, 93% and 96% of bivalve individuals). Predatory gastropods included 61-70% of Duplin gastropod genera, with the Robeson site comparable in genera (68%) but with more individuals (37% vs 28%). Acme and Neils Eddy had 24-26% predatory gastropod individuals, similar to the Duplin, but Holloman had 59% predatory gastropod individuals. When data are combined for all sites, predators were 66%, 70%, and 44% of Duplin, lower and upper Waccamaw gastropod genera (30%, 47% and 27% of individuals). Gastropod:bivalve ratio was 0.16, 0.32 and 0.09 for the three units.