Chemical control of epibiosis by Hong Kong sponges: the effect of sponge extracts on micro- and macrofouling communities

The relationship between antifouling metabolite production and epibiosis on the surfaces of the sponges Haliclona cymaeformis, Haliclona sp. and Callyspongia sp. was investigated in this study. Densities of macrofoulers and diatoms were suppressed on the surfaces of all examined sponges, while densities of bacteria on the surfaces of H. cymaeformis and Callyspongia sp. were similar to those on the reference surfaces and were more than double the densities of bacteria on the surfaces of Haliclona sp. compared with a reference surface. Bray-Curtis similarity matrices of the tRFLP (terminal restriction fragment length polymorphism) analysis of PCR-amplified bacterial 16S rRNA genes obtained from the surfaces of the sponges demonstrated that the bacterial communities on the sponge surfaces were different from each other and from those on the reference surfaces. In field experiments, both methanol and dichloromethane extracts from all tested sponges incorporated in a Phytagel matrix inhibited recruitment of diatoms, algae and invertebrates, but extracts of only 2 sponges deterred bacterial film development. The tRFLP analysis revealed that the sponge extracts decreased diversity in the bacterial community. Strong negative effects of the sponge extracts on the Shannon-Wiener diversity values, as well as the species-richness values of the diatom community were found. ANOSIM (analysis of similarity) and SIMPER (similarity percentage) analyses demonstrated that the type and species specificity of the extracts affected the diatom composition. Results suggest that metabolites of sponges can control recruitment of propagules, change the composition of micro- and macrofouling communities and, in this way, regulate epibiosis on sponge surfaces.