Behaviour patterns as natural antifouling mechanisms of tropical marine crabs

The investigations focused on defence (antifouling) adaptations of seven brachyuran species from the Gulf of Thailand against epibionts (bacteria, diatoms, protozoans, macroorganisms). The species were Calappa philargius (Calappidae), Scylla serrata, Charybdis anisodon, Podophthalmus vigil (Portunidae), Hexapus anfractatus (Goneplacidae), Etisus c.f. laevimanus (Xanthidae) and Metapograpsus quadridentatus (Grapsidae). Carapaces of free living crabs were less densely colonized by organisms than other submerged living and inanimate hard substrata in the same region. The significance of potential mechanical (moulting or sloughing, grooming), physical (surface tension), chemical (surface pH, bioactive compounds), behavioural (hiding, burying, night activity) and ecological (grazing by gastropods) mechanisms was assessed. No evidence was found for an antifouling role of surface pH, toxins, surface tension or carapace grazing by gastropods. Intermoult duration was too long to explain low infestation rates although moulting eventually interrupted the colonization process. The present results indicate that behaviour patterns of the crabs are most effective mechanisms for restricting epibiont colonization. These behaviour patterns include burying in the sediment, hiding in rock crevices or below stones, night-time activity and exposure to air (intertidal species). Burying impedes epibiont access to the body surface and may cause mechanical abrasion. Nocturnal activity, as well as preference for shaded habitats reduces algal growth. Intertidal crabs are protected against the settling stages when foraging above the water line. During emersion, epibionts are also subjected to desiccation stress.