MEPS 189:149-158 (1999)  -  doi:10.3354/meps189149

ABSTRACT: Most studies involving UVB radiation effects in the marine environment have focused mainly on planktonic communities. Despite the importance of shallow-water sediments as nursery and feeding areas for various taxa, investigations of the impact of UVB radiation on meiobenthic communities are still scarce. A microcosm experiment was conducted over a 42 d period with a microbenthic community in a tidal mudflat of the Lower St. Lawrence Estuary, Canada, in order to assess the influence of ambient UVB radiation on the abundance of ontogenic stages of harpacticoid copepods, on nematodes, and on chlorophyll a and pheopigment concentrations. The microbenthic community within non-perturbed sediment cores was exposed to 2 different light regimes: natural irradiance (natural UVB) and reduced UVB. Sampling of the sediment cores was carried out on a weekly basis. There was a significant decrease in chlorophyll a concentrations in reduced UVB microcosms on Days 7 and 14, and no significant difference thereafter. A negative impact of UVB was observed upon meiobenthic copepod nauplii and copepodites. Adult harpacticoid copepods were significantly less abundant in the reduced UVB treatment on Day 7. There was no significant difference in the abundance of adult harpacticoid copepods between treatments at subsequent sampling dates and no effect on nematode abundance for the whole experiment. Our results suggest that natural UVB radiation may have a deleterious effect on the naupliar stages of harpacticoid copepods, a key group of the meiobenthic compartment. Thus, a change in UVB radiation may greatly influence the dynamics of intertidal populations of copepods by affecting their recruitment. Since meiofauna plays a key role in energy fluxes throughout the benthic food web, structural changes of harpacticoid populations induced by UVB radiation may significantly reduce nutrient transport at the water-sediment interface and the availability of food in the upper trophic levels.

KEY WORDS: Ultraviolet radiation · Intertidal mudflat · Harpacticoid copepods · Nematodes · Microphytobenthos · Microcosms