RELATIONSHIPS BETWEEN BODY SIZE AND TAPHONOMIC SIGNAL IN THE PREDATOR-PREY INTERACTIONS OF LAND CRABS AND SNAILS ON SAN SALVADOR ISLAND, THE BAHAMAS

This study seeks to understand the predator-prey interactions between Bahamian land crabs and their prey snails, with a focus on predator and prey body size and its effect on the fossil record of biotic interactions. A total of 22 land crabs (17 Geracinus lateralis, 3 G. ruricola, and 2 Coenobita clypeatus) of varying sizes were collected at San Salvador Island (The Bahamas) and kept in separate enclosures at the Gerace Research Centre. Each crab was provided with a selection of live land snails (Cerion spp. and Hemitrochus varians). In addition, some crabs were provided with plant matter (two leaves of the sea grape, Coccoloba uvifera). All attacks and plant matter feeding events were recorded and the resulting shell material was analyzed for breakage patterns. This fresh shell material was then compared with the fossil remains of Upper Pleistocene land snails from Sand Salvador Island.

Results indicate a statistically significant preference for H. varians, which has a thinner and more fragile shell compared with the more robust skeleton of Cerion spp. Larger land crabs preferentially attacked Cerion spp., consumed snails more frequently, and destroyed shell material more thoroughly in their attacks. Shells were most frequently destroyed through crushing. Comparison of fresh shell material to fossil shell material revealed similar frequencies of peeling and piercing. However, crushing attacks were difficult to identify in the fossil record. This difficulty may represent an important source of bias, which would lead paleobiologists to underestimate the extent of land crab predation. In addition, by preferentially preying on H. varians and other lightly shelled land snails, Bahamian land crabs may be contributing to the dominance of Cerion spp. in the island’s fossil record.

To successfully interpret the fossil record of terrestrial mollusks on San Salvador Island, it is essential to consider the influence of land crab predation, and in particular, the way that body size may control predatory behavior.