Defenses of Caribbean sponges against invertebrate predators. I. Assays with hermit crabs

Hermit crabs (Decapoda: Anomura) are typically omnivorous and are common on Caribbean coral reefs. Sponges are sessile, fleshy, and high in protein an d energy content, yet hermit crabs do not appear to prey on them. Assays we re performed with the Caribbean reef hermit crab Paguristes punticeps to de termine whether secondary metabolites or skeletal elements of Caribbean spo nges that were incorporated into artificial foods affected feeding. Of 30 s ponge species assayed, 26 (87%) yielded organic extracts that deterred feed ing by P. punticeps. There was substantial interspecific and intraspecific variability in patterns of chemical deterrence. Sponges of the families Axi nellidae, Agelasidae, Aplysinidae, Aplysinellidae, and Thorectidae typicall y yielded deterrent extracts. Three common sponge species, Mycale laevis, C allyspongia vaginalis, and Niphates erecta, were consistently non-deterrent , while other species, including Spheciospongia othella, Chondrilla nucula, Callyspongia plicifera, Niphates digitalis, and Xestospongia muta, were va riably deterrent. These results are in general agreement with those of a pr evious survey of Caribbean sponge chemical defenses using the common reef f ish Thalassoma bifasciatum. However, some results differed: Geodia neptuni and Iotrochota birotulata were consistently palatable to T. bifasciatum, bu t were deterrent to P. punticeps. Several species that were consistently de terrent to T. bifasciatum were variably deterrent to P, punticeps, includin g Aplysina cauliformis, Aplysina fulva, Ircinia strobilina, Amphimedon comp ressa, and Mycale laxissima. Neither spicules (from Agelas clathrodes, Ecty oplasia ferox, and Xestospongia muta) nor spiculated spongin skeleton (from A. clathrodes and X. mute) deterred feeding by P. punticeps. Spicules and spiculated spongin were similarly non-deterrent to the fish T. bifasciatum in a previous survey. The results of this study further suggest that chemic al defenses are important in the ecology of Caribbean sponges, while skelet al components do not serve an antipredatory function.