Community responses to UV radiation. I. Enhanced UVB effects on biomass and community structure of filamentous algal assemblages growing in a coral reef mesocosm

Abstract

Four treatments (PAR; PAR+UVA; PAR + UVA+UVB enhanced by 20% from ambient levels; ambient levels of UVB) were performed using a combination of metal halide lights, UV lamps and cutoff filters over developing assemblages of filamentous algae in a coral reef mesocosm. Exposure to enhanced UVB initially reduced the standing crop by 67% as compared to the productivity of the assemblages grown under PAR and PAR+UVA. Treatment reversal from PAR to enhanced UVB restricted temporarily the growth of the brown alga Ectocarpus rhodochondroides. While the spores of this species are inhibited by UVB, the sporophytes seem to be capable of adapting to UVB exposure. The effects of ambient UVB levels on biomass production and community composition were less pronounced, while exposure to UVA did not affect productivity or community composition. All effects due to UVB exposure gradually diminished as succession progressed. Community composition and biomass production were fully restored 1 to 2 weeks after the cessation of exposure to enhanced UVB.