Abstract
Secondary metabolites protect many marine sponges ( P hylum: P orifera) from settlement by fouling organisms. Previous studies on the subtidal demosponge A xinella verrucosa collected in the W estern M editerranean led to the isolation of compounds that inhibited the settlement of cyprids larvae of the intertidal barnacle B alanus amphitrite , and the enzyme chitinase, which plays a key role in the molting cycle of crustaceans. However, in a field survey conducted at three locations in I srael, E astern M editerranean S ea, we observed that A . verrucosa is fouled by the subtidal barnacle B alanus trigonus , a previously unknown association. Settlement inhibition assays using B . amphitrite with chemical extracts from I sraeli A . verrucosa and A xinella polypoides , a sympatric, congeneric sponge that seems not to be fouled by B . trigonus , showed that cyprid larvae of B . amphitrite were inhibited by the extracts of both sponges from settlement at concentrations several magnitudes lower than natural volumetric extract concentration in the sponges. These results indicate that, unlike the intertidal barnacle B . amphitrite , the subtidal B . trigonus is unaffected by the compounds from A . verrucosa , stressing and underlining the importance of using suitable target organisms ( i.e . from the same habitat) to test for ecologically relevant antifouling activities.