Defenses of Caribbean sponges against invertebrate predators. II. Assays with sea stars

Abstract

Sea stars are dominant predators in many marine habitats, and spongivory by sea stars has been documented from polar seas to the tropics. Feeding assays of whole tissue and artificial foods containing organic extracts, spicules, and spiculated skeleton of sponges were performed with the Caribbean sea stars Echinaster echinophorus (from the Bahamas) and Echinaster sentus (from Florida, USA) to determine whether sponge secondary metabolites or skeletal constituents affect feeding by sea stars. Whole tissue assays of 6 species of mangrove sponges yielded similar preference hierarchies for both sea star species: for E. echinophorus, Tedania ignis = Haliclona hogarthi? Ircinia felix = Dysidea etheria > Chondrilla nucula = Chondrosia collectrix; for E. sentus, T. ignis = H. hogarthi > I. felix = D. etheria = C. nucula = C. collectrix. Whole tissue assays of 5 species of reef sponges yielded identical hierarchies for both E. echinophorus and E. sentus: Geodia neptuni > Callyspongia vaginalis > Amphimedon compressa = Ectyoplasia ferox = Agelas clathrodes. Crude organic extracts of the same 6 mangrove sponge species were assayed, and only the crude organic extracts of Dysidea etheria deterred feeding by E. echinophorus. Extracts of I. felix, which consistently deterred both fishes and hermit crabs in previous studies, did not deter E. echinophorus. Extracts of the same reef sponge species were assayed, and only A. clathrodes, E. ferox, and A. compressa deterred feeding by E. echinophorus. In whole tissue assays with E. sentus of chemically non-defended species (sponges that yielded organic extracts palatable to E. echinophorus) from both reef and mangrove habitats, all species were consistently preferred over C. nucula. The preferences of E. sentus for chemically non-defended species did not correlate with sponge nutritional or skeletal content, suggesting that other characteristics of these sponges influence sea star preferences. Spicules from 5 species of reef sponges (G. neptuni, C. vaginalis, A. clathrodes, E. ferox, and A. compressa) and 3 species of mangrove sponges (T. ignis, H. hogarthi, and C. nucula), and whole sponge skeleton from 4 species of mangrove sponges (T. ignis, I. felix, C. nucula, and C. collectrix) did not deter feeding by E. echinophorus. These results, when considered with the data from previous studies employing fishes and hermit crab assays, further illustrate the importance of secondary metabolites as antipredatory defenses for Caribbean sponges.