Effects of ultraviolet-B radiation and nutrient enrichment on the productivity of benthic microalgae in shallow coastal lagoons of the North Central Gulf of Mexico

Benthic microalgae (BMA) play important roles in shallow coastal systems. Few studies have addressed the combined effects of ultraviolet-B radiation (UVB) and nutrient enrichment on the productivity of BMA. Here we use field and microcosms experiments to explore the single and combined effects of ambient and increased UVB and sediment nutrient enrichment on the productivity of BMA in two shallow coastal lagoons of the North Central Gulf of Mexico. We found few negative effects of ambient and increased UVB levels, even though increased UVB levels were higher than liberal predictions of anthropogenic increase for the studied area. In contrast, we found several positive effects of sediment fertilization, although all positive effects were restricted to one of the lagoons. These results point to strong protective responses of BMA to UVB in the lagoons studied. Such protective responses do not appear to be limited by ambient nutrient availability. This study indicates that sediment nutrient enrichment is a more important driver for BMA, and by default for the ecological functioning of the lagoons studied, than current and predicted UVB levels. These conclusions, however, may not apply to other coastal systems, where the interactive effects of fertilization and UVB on BMA deserve further investigation.