The sesterterpene variabilin as a fish-predation deterrent in the western Atlantic sponge Ircinia strobilina

The furanosesterterpene variabilin was identified in an unpalatable crude e xtract and proved to be a feeding deterrent when offered at 0.23% of artifi cial diet dry weight to reef fishes in field assays. The icthyodeterrent pr operty of variabilin was expressed when food pellets for the palatability a ssays were made with calcium alginate, but not carrageenan. Variabilin prob ably failed to show deterrent activity in the carageenan matrix because of decomposition during the necessary heat treatment.