Abstract
In this study, we link laboratory results with field evidence of microbial settlement responses to crude extracts of several sponge species from Hong Kong waters, including Cally- spongia sp. 1, Callyspongia sp. 2, C. pulvinata, Mycale adhaerens, Haliclona cymaeformis var. 1, H. cymaeformis var. 2 and Halichondria sp. (Porifera: Demospongiae). Laboratory experiments showed that 6 out of 7 sponge extracts inhibited growth and caused mortality of the pennate diatom Nitzschia paleacea at tissue-level concentration. In disk-diffusion bioassays, extracts of the sponge Halichon- dria sp. inhibited the growth of 4 bacterial strains out of 11 isolated from inanimate substrata; other sponge extracts inhibited growth of only 1 or 2 bacterial strains. For field experiments, sponge metabolites were immobilized in a Phytagel ® matrix and exposed to natural microbial communities. After 2 d of exposure, bacterial densities on the gels with sponge extracts were lower than on control gels. Terminal restriction fragment length polymorphism (TRFLP) analysis of PCR-amplified bacter- ial community 16S rRNA genes obtained from these gels demonstrated that the communities were different between the sponge extracts and control gels. After 7 d of exposure, 6 (86%) extracts suppressed the recruitment of pennate diatoms and 3 (43%) sponge extracts suppressed the recruit- ment of bacteria. These results suggest that sponge extracts can modify the structure of bacterial communities and decrease the density of bacteria and diatoms in microfouling communities.
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