Exudation of biologically-active metabolites in the sponge Aplysina fistularis

Substances exuded by the intertidal sponge Aplysina fistularis (Pallas, 1776) from San Diego, California, USA, were collected with open (flowing) and closed seawater systems. The exudates were tested in bioassays for: (1) behavior modifications of invertebrate adults, including a hydroid, an ectoproct, a limpet and a sea star, (2) toxicity to dorid nudibranchs (three species), (3) inhibition of sexual reproduction in a brown alga, and (4) inhibition of settlement and/or metamorphosis of late larvae or juveniles, including an ectoproct, a polychaete and a gastropod. Exudates inhibited metamorphosis of gastropod veliger larvae and caused behavior modifications in all invertebrate adults, but were not toxic to dorid nudibranchs. It is proposed that exudates help protect A. fistularis from surface overgrowth by fouling organisms and from tissue damage by mobile animals.