CLIMATE CHANGE AND THE RESPONSE OF SHELL-CRUSHING PREDATORS FROM THE EOCENE OF SEYMOUR ISLAND, ANTARCTICA

Today the nearshore, benthic fauna in Antarctica is dominated by epifaunal suspension feeders and the absence of fast-moving, shell-crushing predators, such as sharks and crabs. This unique food-web structure was established about 41 million years ago during the Eocene as temperatures started to cool and shell-crushing predators were excluded from Antarctic waters (Aronson, 2009). Here we use the trace-fossil record of predation preserved on gastropod shells from the Eocene La Meseta Formation on Seymour Island off the Antarctic Peninsula to assess the effect of climatic cooling on shell-crushing predator-prey interactions. We predicted that the frequency of shell repair—the percentage of shells with at least one repaired injury—would decrease as the climate cooled and shell-crushing predators were reduced in abundance and ultimately excluded from the benthic community. Analysis of more than 1,250 gastropod specimens showed a significant decrease in average repair scar frequency, from 22% to 2%, across the cooling event. The range of variation of repair frequencies for individual taxa before and after the cooling event also showed a significant degree of non-overlap. These findings support the hypothesized decline in importance of shell-crushing predation in structuring benthic communities after the cooling event due to exclusion of these predators.