Antilarval and antimicrobial activity of waterborne metabolites of the sponge Callyspongia (Euplacella) pulvinata: Evidence of allelopathy

Antilarval, antidiatom and antibacterial activity of sponge metabolites has been well documented in previous laboratory experiments. In this investigation we attempted to link the results of our earlier laboratory experiments of antifouling activity of the sponge Callyspongia (Euplacella) pulvinata (Porifera: Demospongiae, Haliclonidae) to those measured in the field. Our laboratory experiments showed that conditioned seawater (CSW) of the sponge strongly inhibited the growth of the benthic diatom Nitzschia paleaceae and the settlement of the tubeworm Hydroides elegans, but had no effect on the growth of 9 bacterial strains isolated from natural biofilms. When diluted 5 times, the CSW still exhibited antilarval and antidiatom activities. In field experiments, sponge specimens were placed within 13 and 50 cm of Petri dishes that were serving as attachment substrates for micro-and macrofouling organisms. Synthetic sponge-like material was used to mimic sponges for the controls. The results showed that after 7 d, diatom attachment on dishes placed in close vicinity to the sponge was inhibited. Bacterial densities on the experimental dishes did not differ significantly (p > 0.05) from those in the control dishes. Microfouling communities, which developed on both experimental and control dishes in the field, had similar effects on the settlement of H. elegans under laboratory conditions. After 28 d, an early community had been established, consisting of 5 species of green algae, 2 species of brown algae, 2 species of red algae and 5 species of invertebrates. We found strong negative effects of the presence of sponges and the position of the plate on the total percentage of cover, Shannon-Wiener diversity, as well as on the species richness of macrofouling communities. In the experimental dishes, the percentage of coverage of both macroalgae (Ulva sp., Ectocarpus sp., Enteromorpha sp., unidentified brown algae) and invertebrates (Obelia sp., H. elegans) decreased. ANOSIM (analysis of similarity) and a SIMPER (similarity percentage) analysis demonstrated that the composition of macrofoulers on the dishes were positively affected both by the presence of a sponge and with decreasing distance from it. Our results suggest that waterborne compounds of C. pulvinata inhibit settlement of micro- and macrofoulers not only on its own surface but also on non-living surfaces nearby.