Effects of UV-B radiation on carbon and nutrient dynamics in marine plankton communities

Four indoor model ecosystems with natural plankton communities have been run. Two of the systems are exposed to artificial photosynthetic active radiation (PAR, 20 W m(-2) for 16 h per day) and UV-B radiation (approximate to 0.64 W m(-2) for 6 h per day), while the other two are exposed to PAR only. Photosynthesis, nitrogen uptake, nutrient concentrations and contents of chlorophyll, particulate carbon, nitrogen and phosphorus are followed for six days. Photosynthesis and chlorophyll content are significantly reduced by the UV-B radiation, whilst uptakes of nitrate and ammonia are less affected. The contents of particulate carbon, nitrogen and phosphorus are always as high, or higher, in the UV-B-exposed communities as in the controls, while the content of chlorophyll a is reduced. Together with an increased cell number of bacterial predators, this indicates that the biomass of heterotrophs is enhanced in the UV-B-exposed communities. (C) 1998 Elsevier Science S.A. All rights reserved.