Understanding the distribution and densities of ghost crabs (Ocypode spp.) to improve management of hawksbill turtle Eretmochelys imbricata nesting sites

Abstract

Predation on sea turtle nests is a natural occurrence at nesting beaches worldwide, with various animals consuming the eggs and hatchlings as part of the ecosystem. Cousine Island in the Seychelles Archipelago is an important nesting site for the Critically Endangered hawksbill turtle Eretmochelys imbricata in the western Indian Ocean; however, certain beach areas may experience losses of eggs and hatchlings of 90–100%. This study aimed to determine whether seasonal beach transformation or changes in the population density of ghost crabs (Ocypode spp.) affect the rate of predation on hawksbill turtle nests along Cousine’s singular beach, and, if so, to what extent. We found that the highly dynamic beach directly affects crab density across the length of the beach, with a significant negative relationship between beach width and crab density. Although the densities and levels of activity and predation of ghost crabs vary along the beach, crab density did not appear to influence the rate of their predation on hawksbill turtle nests on the island. Our results have allowed us to identify sites along Cousine’s beach with lower levels of ghost crab activity and predation on hawksbill turtle nests, which will enable conservationists to relocate nests to safer sites, thereby providing a valuable tool to minimise nest losses and improve sea turtle recruitment.