Effect of solar ultraviolet radiation on the formation of shallow, early successional biofouling communities in Hong Kong

The effect of ambient solar ultraviolet radiation (UVR) on a shallow-water (4 cm) tropical fouling community was assessed during the succession of macrobenthic species on artificial substrates at the Wong Shek fish farm, Hong Kong. The early successional communities developing under 3 radiation treatments (PAR + UV-A + UV-B = 280 to 700 nm; PAR + UV-A = 320 to 700 nm, and PAR = 400 to 700 nm) were monitored for 14 wk. A total of 8 species of algae and 8 species of invertebrates colonised the experimental tiles. During the first 8 wk of the experiments, there were no differences among treatments in diversity, percentage of cover of species and the biomass of the colonisers. During the following 6 wk, the communities exposed to UVR had lower species richness than the communities exposed to only PAR had. The species diversity (after 79 and 98 d) of the 3 treatments varied, but the total percentage of species cover and the entire community biomass were not significantly different across the experiment. Juveniles of the polychaete Hydroides elegans and the barnacle Balanus amphitrite, juveniles of the clams Perna viridis and Modiolus comptus, and the algae Enteromorpha sp., Ectocarpus sp. and Cladophora sp. were responsible for the dissimilarity between communities developed under different UVR treatments. The algae constituted a higher percentage of the cover under the full sunlight spectrum, whereas the polychaete, the barnacle and the clams were dominant in the no-UVR treatment. Our outdoor experiment revealed that UVR inhibited the settlement and decreased post-settlement survival of H. elegans. We concluded that UVR affects the composition of early successional, shallow water biofouling communities in tropical waters as well as the settlement and mortality of single species.