Stability of Late Pleistocene Reef Mollusks from San Salvador Island, Bahamas

Stability of Cenozoic reefs has been documented previously by assessing stability of coral assemblages; however, the stability of other components of reef communities, such as mollusks, is unknown. To investigate whether reef mollusksform stable associations of species, mollusks from a reef decimated by brief sea-level fall within the Sangamon interglacial were compared to those of the reef that reassembled when sea level returned (after 1100-1500 years) at Cockburn Town, San Salvador Island, Bahamas. Additionally,
to investigate whether mollusks within reefs were unique to that environment, assemblages from fossil reefs were compared to the assemblage of the adjacent subtidal carbonate-sand facies. A total of 54 species and 4832 individuals were observed within twenty-one quadrats of both reefs and the subtidal sand. Taphonomic alteration was documented to determine if taphonomic histories were similar. Taxonomic composition of assemblages was compared with Detrended Correspondence Analysis. To test whether reef mollusk assemblages were distinctive and recurring, MANOVA tests were performed on transformed data with rare taxa excluded. Two null hypotheses were evaluated: (1) H0: there is no difference in mollusks from different reef building episodes, suggesting stability; and, to test if assemblages from reefs are unique, (2) H0: there is no difference in mollusks from reefs and subtidal sands. Reef mollusk assemblages from different periods of reef building were not significantly different. Additionally, reef mollusks formed unique assemblages that were distinct from those of adjacent subtidal sand areas. Taphonomic differences between deposits were minor. Reef mollusks followed the same pattern of stability that has been documented for coral assemblages over longer time intervals. Therefore, despite community reassembly during the late Pleistocene, mollusks associated with the reef communities show evidence of stability.