Ultraviolet-B Radiation Effects on Natural Phytoplankton Assemblages of Central San Francisco Bay

Since the discovery of a depletion of the stratospheric ozone layer over Antarctica in 1979, scientific attention has been directed towards the effects of increased doses of ultraviolet radiation on phytoplankton in other ecosystems. Little is known about the effects of ultraviolet-B (280-320 nm) radiation (UVBR) on temperate estuarine phytoplankton. Freshly collected phytoplankton samples from Central San Francisco Bay were exposed to ambient UVBR in quartz bottles and monitored for biomass and nutrient uptake rates for comparison with phytoplankton dispensed into bottles made of polycarbonate that effectively filtered out the UVBR to evaluate response to natural UVBR exposure. Short-term (10-12 h) exposure experiments were carried out monthly from October 1998 to October 1999. No significant effect of UVBR on chlorophyll a concentrations was found but a clear deleterious effect of UVBR on nutrient uptake was observed.