Sea Turtle Eggs and Hatchlings are a Seasonally Important Food Source for the Generalist Feeding Golden Ghost Crab (Ocypode convexa)

• Published in: Estuaries and coasts 2024-05, Vol.47 (3), p.821-838
• Main Authors: Avenant, Casper, Fossette, Sabrina, Whiting, Scott, Hopkins, Anna J. M., Hyndes, Glenn A.
• Format: Article
• Language: English
• Subjects: Algae; Aquaria; Aquarium fishes; Aquariums; Aquatic reptiles; Beaches; Caretta caretta; Carnivorous animals; Carrion; Coastal Sciences; Content analysis; Crustaceans; Deoxyribonucleic acid; Diet; DNA; Earth and Environmental Science; Ecology; Eggs; Environment; Environmental Management; Feeding experiments; Feeding trials; Fish; Food chains; Food sources; Food webs; Freshwater & Marine Ecology; Juveniles; Marine crustaceans; Nesting; Nutrient cycles; Nutrients; Ocypode convexa; Ocypodidae; Phaeophyceae; Reptiles & amphibians; Rookeries; Sea turtles; Stable isotopes; Survival; Turtles; Water and Health; World Heritage Areas
• ISSN: 1559-2723; 1559-2731
• DOI: 10.1007/s12237-023-01309-4

Ghost crabs can be abundant at beaches where sea turtles nest, but the food web dynamics are poorly understood. Using multiple dietary methods, our research aimed to characterise the diet of the golden ghost crab Ocypode convexa at rookeries of the loggerhead turtle Caretta caretta on the west coast of Australia, with a focus on determining the importance of sea turtle eggs and hatchlings to its diet. We achieved this through combining complementary methods: gut content analysis (GCA); DNA analysis of gut contents; stable isotope analysis (SIA); and controlled feeding experiments. GCA showed that O. convexa is a facultative scavenger with an omnivorous diet comprising high contributions (> 55%) of abundant beach-cast leafy brown algae. However, DNA analysis identified C. caretta in ≥ 20% of crab guts, and stable isotope mixing models suggested that sea turtle contributed 40–62% of assimilated C and N for male and 21–40% for female ghost crabs during the nesting season, while other animal and algal sources were also likely to be consumed when sea turtle eggs and hatchlings were absent or present. Aquarium-based feeding assays showed that ghost crabs prefer sea turtle and fish carrion over leafy brown algae (0.81 vs 0.10 vs 0.03 g/h consumed). Sea turtles provide large amounts of nutrients to consumers in the form of eggs and hatchlings, and golden ghost crabs benefit substantially from this pulsed resource along the Ningaloo coast, a World Heritage Area. Through the combined use of SIA, GCA, DNA, and feeding trials, this study highlights the important roles of both sea turtles and ghost crabs in energy fluxes and nutrient cycling at generally nutrient-poor sandy beach ecosystems. However, high consumption rates in the region can possibly put the long-term survival of the C. caretta population at risk.