Ultraviolet-B radiation enhancement does not affect marine trophic levels during a winter-spring bloom

Abstract

:Elevated UV-B radiation levels (~100% above ambient) generally failed to produce significantly different effects at different trophic levels in well-mixed mesocosms during the winter spring bloom period. Although not significantly different, several consistent trends were noted. Phytoplankton abundance, measured as total cell counts, and biomass, measured as in vivo fluorescence, tended to be reduced in UV-B enhanced treatments. Effects were significantly different for fluorescence (p < 0.05) during the bloom event but not abundance (p = 0.29) and not over the entire experiment. There was a tendency for the ratio of nanoplankton to microplankton biomass to be lower in UV-B enhanced systems (p = 0.16). Total copepod abundance (adults, copepodites and nauplii) and abundance of the dominant species, Acartia hudsonica (Giesbrecht), also tended to be lower in the treatment mesocosms. Significant differences (p < 0.05) in copepod abundance between controls and treatments were observed in the adult stage prior to and during the bloom event. Survival of winter flounder (Pleuronectes americanus [Walbaum]) eggs incubated at 0.1 and 0.5 m depths was significantly lower in UV-B elevated mesocosms (p < 0.05) while no significant differences were observed at greater depths (p = 0.55). Survival and growth of winter flounder larvae added to the mesocosms during the final three weeks of the experiment did not vary significantly between controls and treatment mesocosms.