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 and energy content, yet hermit crabs do not appear to prey on them. Assays were performed with the Caribbean reef hermit crab Paguristes punticeps to determine whether secondary metabolites or skeletal elements of Caribbean sponges that were incorporated into artificial foods affected feeding. Of 30 sponge species assayed, 26 (87%) yielded organic extracts that deterred feeding by P. punticeps. There was substantial interspecific and intraspecific variability in patterns of chemical deterrence. Sponges of the families Axinellidae, Agelasidae, Aplysinidae, Aplysinellidae, and Thorectidae typically yielded deterrent extracts. Three common sponge species, Mycale laevis, Callyspongia vaginalis, and Niphates erecta, were consistently non-deterrent, while other species, including Spheciospongia othella, Chondrilla nucula, Callyspongia plicifera, Niphates digitalis, and Xestospongia muta, were variably deterrent. These results are in general agreement with those of a previous survey of Caribbean sponge chemical defenses using the common reef fish Thalassoma bifasciatum. However, some results differed: Geodia neptuni and Iotrochota birotulata were consistently palatable to T. bifasciatum, but were deterrent to P. punticeps. Several species that were consistently deterrent to T. bifasciatum were variably deterrent to P, punticeps, including Aplysina cauliformis, Aplysina fulva, Ircinia strobilina, Amphimedon compressa, and Mycale laxissima. Neither spicules (from Agelas clathrodes, Ectyoplasia 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 chemical defenses are important in the ecology of Caribbean sponges, while skeletal components do not serve an antipredatory function.