16 Undergraduate Research (Posters)

Friday, 13 March 2009
8:30 AM - 12:30 PM

EFFECTS OF A LATE PLIOCENE EXTINCTION IN NORTH CAROLINA ON MOLLUSK DIVERSITY AND ECOLOGY: PRELIMINARY RESULTS

Paper number: 16-5
Program: Theme Sessions
Time: 8:30 AM – 12:30 PM

Authors

Abstract

The Plio-Pleistocene was a time of extinction in the western Atlantic, but timing and cause of the extinction and nature of recovery are not well understood, especially for the Carolinas. As part of a Research Experiences for Undergraduates study, we compared diversity and ecological structure for the Duplin Formation (prior to the extinction) and the lower Waccamaw Formation (following the initial turnover pulse). Bulk samples were collected from a Duplin exposure along the Lumber River near Lumberton, NC, and from the Waccamaw at Register Quarry near Old Dock, NC. Samples were sieved through a quarter-inch mesh and specimens picked, sorted and identified to genus level; life modes were assigned using the NMITA molluscan life modes database.

Richness decreased from the Duplin to the Waccamaw, consistent with an episode of extinction; ~4700 Duplin bivalve specimens yielded 66 genera compared to 63 genera (~8100 specimens) in the Waccamaw. Forty-four gastropod genera were identified from the Duplin (488 specimens) vs. 38 Waccamaw gastropod genera (854 specimens). Rarefaction analyses indicate the differences in richness are significant.

In contrast, trophic structure was similar for the two formations. The percent of suspension feeding genera (~48%) and suspension feeding individuals (~87%) was the same for the two formations. Suspension feeding bivalves represented ~72% of bivalve genera and 95% of bivalve individuals for both formations. Predators constituted ~26% of all genera for both formations; predators represented 4.8% of Duplin and 7.2% of Waccamaw individuals (a statistically significant difference). Predatory gastropods included 61% of Duplin gastropod genera (28% of gastropod individuals) and 66% of Waccamaw gastropod genera (41% of gastropod individuals). The percent of predatory gastropod genera did not differ significantly between formations, but the Waccamaw had a significantly greater percent of predatory gastropod individuals. Although preliminary, the results suggest that, though richness declined between the Duplin and lower Waccamaw samples, most measures of trophic structure did not change significantly (suggesting the decline in richness was not related to nutrient levels). Future work will examine samples from additional localities to test the robustness of the pattern.