Ontogenetic trophic variation in ghost crab Ocypode quadrata

Abstract

Changes in food resource use over an organism's lifespan play a pivotal role in structuring trophic webs. Although substantial evidence suggests that many benthic invertebrate species undergo ontogenetic dietary shifts, this process remains scarcely studied in sandy beach species. Ocypode quadrata is the unique ghost crab species in the Western Atlantic and exhibits generalist feeding habits, playing a key role in energy transfer across trophic levels and connecting coastal ecosystems. We analyzed stomach contents and δ¹⁵N and δ¹³C stable isotopes from juveniles and adults of O. quadrata to test the hypothesis of size-dependent niche shifts. Sediment and unidentified organic matter were the most commonly detected items in stomach contents. Adults consumed the mole crab Emerita brasilienis more frequently (63 %), a prey absent in juvenile stomachs, whereas insects were more prevalent in juveniles (78 %). Microplastics were detected in over one-third of juveniles, indicating their exposure to marine litter contamination. Similar δ¹⁵N values suggest that adults and juveniles occupy similar trophic levels, sharing a large portion of their diet, though assimilation frequencies or magnitudes may differ. Our results support the hypothesis that adults have a broader trophic niche than juveniles, likely reflecting greater ability in exploiting a wider range of food resources. The broader isotopic niche in adults aligns with their higher consumption of E. brasilienis. The assimilation of both marine and terrestrial resources reinforces the meta-ecosystem framework, highlighting the ecological importance of allochthonous inputs to sandy beach ecosystems and underscoring the need for landscape-scale conservation strategies.