HIGH PREDATION RATES ON A CARBONATE TIDAL FLAT, CAT ISLAND, BAHAMAS

Initial analysis of shells collected on a tidal flat on Cat Island, Bahamas, in January, 2009, suggests that predator-prey interactions in tidal flat environments are different, and perhaps more intense, than those in nearby open ocean shallow subtidal settings. After initial collection on the tidal flat, a subsample of 1700 shells was analyzed. These shells were collected in a mangrove tidal flat at the low tide zone. This assemblage is dominated by small gastropods with only 29 total disarticulated bivalve shells preserved in our subsample. Of the 1700 examined shells, 44% of the gastropods are bored while 21% of the bivalve shells were bored. The most abundant species in this assemblage include Batillaria minima, Cerithidea coasata, Cerithiopsis carpenteri, and Codakia cosata. Other Cerithium and Batillaria sp. are present but are too taphonomically altered to make a species-level identification. The shells are all small in size and range from 1.66mm to 16.52mm, which is consistent with a tidally-influenced environment. The suspected predator, based on the abundance of beveled holes in prey shells and presence in our assemblage, is Polinices sp.

In many important ways, this assemblage differs from nearby shallow subtidal settings. The number of gastropods compared to bivalves collected from the tidal flat is much greater than what has been observed in nearby subtidal environments on Cat Island. Subtidal settings contain diverse bivalve assemblages that represent a wide range of ecologies; the tidal flat assemblage is lower in diversity and dominated by small, stress-tolerant gastropods. Interestingly, in the tidal flat assemblages, 44% of gastropod shells are drilled whereas the highest rates of predation observed in subtidal settings in other areas of the Bahamas is ~20%. Tidal flat predator-prey interactions are not well understood and appear to be quite different than normal marine beach environments. Future work will focus on determining the environmental and ecological conditions that account for the high rates of predation on gastropods and if high rates of predation in these types of settings can provide paleoenvironmental indicators in the geological record.