DIVERSITY AND ECOLOGICAL STRUCTURE OF THE CANEPATCH FORMATION, UPPER PLEISTOCENE, HORRY COUNTY, SOUTH CAROLINA
The samples in aggregate included 1559 bivalve specimens (26 genera) and 239 gastropods (12 genera). Canepatch 1 was significantly less rich than the other two samples based on rarefaction to 420 specimens (15.6 vs 18 and 19.7 bivalve genera). The gastropods of Canepatch 1 were also less diverse, though 95% confidence intervals overlap among all samples. All samples have very similar ecological structure. Dominance values ranged from 0.28 – 0.33 for bivalves and 0.22 - 0.32 for gastropods; equitability was 0.60 – 0.63 for bivalves and 0.70-0.79 for gastropods. Chione and Crepidula dominated the bivalve and gastropod faunas respectively, and rank order abundances were highly correlated among all samples (p<0.0002) for bivalves and between Canepatch 2 and 4 for gastropods (p < 0.001). Life modes were very similar among bivalve samples, especially Canepatch 1 and 2 (94-95% suspension feeders, 85% infaunal siphonate/semi-infaunal specimens; Canepatch 4 had 91% suspension feeders and infaunal siphonate/semi-infaunal specimens). Gastropod assemblages were all dominated by predatory carnivores (51-57%); Canepatch 1 and 2 had 43% suspension feeding individuals (Crepidula) whereas Canepatch 4 had 36% Crepidula, with some carnivorous browsers and herbivores. Drilling predation accounted for 12 – 19% of bivalve mortality, with Chione consistently drilled (9 – 22%). Mulinia, found only in Canepatch 4, had a 32% drilling frequency. Tellina was also drilled frequently (24% for 37 total specimens). Only one gastropod specimen in Canepatch 1 and 2 was drilled, but 13% of gastropod specimens in Canepatch 4 were drilled.