Trophic ecology of ghost crabs with diverse tastes: Unwilling vegetarians
Centre for Marine Ecosystems Research / School of Science
Food webs on ocean-exposed sandy beaches are almost entirely underpinned by trophic subsidies from the sea. Ghost crabs (Ocypode spp.), which are highly mobile invertebrate consumers that display a diversity of feeding modes, form an important consumer on numerous beaches around the world. However, little is known of their trophic structure and the role they play as vectors for spatial subsidies through movement of marine derived nutrients inland. The aim of this study was to determine the trophic ecology of the Golden ghost crab (Ocypode convexa) and understand what its role is in terms of marine connectivity along the mid-west coastline of Australia. Based on stomach content (percentage frequency (%F) and percentage volume (%V)) and stable isotope analyses (mixing models using ẟ13C and ẟ15N), the dietary composition of O. convexa was typically dominated by brown algae, and complemented by marine and terrestrial vascular plants and arthropods (various insects and amphipods). However, feeding assays revealed that the species had a clear preference for fish and invertebrate carcasses when the choice was offered, indicating a proclivity for the more nutritionally valuable animal flesh when available. Thus, ghost crabs are likely to be unenthusiastic consumers of vegetables, and are likely to feed on algae and macrophyte matter only when animal carrion or live animal prey is sparse. Consistent intake and assimilation of marine matter by ghost crabs, and their likely predation by higher level consumers, such as foxes (e.g. Vulpes vulpes) and birds (e.g. Corvus coronoides), support the concept that they form a vector for cross-boundary fluxes of marine carbon to inland ecosystems, although it needs to be recognized that ghost crabs also derive part of their nutritional requirements from terrestrial sources.