Journal of Chemical Ecology, Vol. 28, No. 6, June 2002 (  C 2002) DOES THE ODOR FROM SPONGES OF THE GENUS Ircinia PROTECT THEM FROM FISH PREDATORS? JOSEPH R. PAWLIK, 1,* GREG MCFALL, 1 and SVEN ZEA 2 1 Biological Sciences and Center for Marine Science Research University of North Carolina at Wilmington Wilmington, North Carolina 28403-3297 2 Universidad Nacional de Colombia (Departamento de Biolog´ ıa) INVEMAR, Cerro Punta de Bet´ ın AA 10-16, Santa Marta, Colombia (Received August 9, 2001; accepted January 31, 2002) Abstract—Caribbean sponges of the genus Ircinia contain high concentrations of linear furanosesterterpene tetronic acids (FTAs) and produce and exude low- molecular-weight volatile compounds (e.g., dimethyl sulfide, methyl isocyanide, methyl isothiocyanate) that give these sponges their characteristic unpleasant garlic odor. It has recently been suggested that FTAs are unlikely to function as antipredatory chemical defenses, and this function may instead be attributed to bioactive volatiles. We tested crude organic extracts and purified fractions isolated from Ircinia campana, I. felix, and I. strobilina at naturally occurring concentrations in laboratory and field feeding assays to determine their palata- bility to generalist fish predators. We also used a qualitative technique to test the crude volatile fraction from I. felix and I. strobilina and dimethylsulfide in labo- ratory feeding assays. Crude organic extracts of all three species deterred feeding of fishes in both aquarium and field experiments. Bioassay-directed fractiona- tion resulted in the isolation of the FTA fraction as the sole active fraction of the nonvolatile crude extract for each species, and further assays of subfractions sug- gested that feeding deterrent activity is shared by the FTAs. FTAs deterred fish feeding in aquarium assays at concentrations as low as 0.5 mg/ml (fraction B, variabilin), while the natural concentrations of combined FTA fractions were >5.0 mg/ml for all three species. In contrast, natural mixtures of volatiles trans- ferred from sponge tissue to food pellets and pure dimethylsulfide incorporated into food pellets were readily eaten by fish in aquarium assays. Although FTAs may play other ecological roles in Ircinia spp., these compounds are effective as defenses against potential predatory fishes. Volatile compounds may serve other defensive functions (e.g., antimicrobial, antifouling) but do not appear to provide a defense against fish predators. * To whom correspondence should be addressed. E-mail: PawlikJ@UNCWil.edu 1103 0098-0331/02/0600-1103/0 C  2002 Plenum Publishing Corporation