Physiological responses of Hizikia fusiformis (Phaeophyta) to mercury exposure

Abstract

Abstract Marine coastal ecosystems are suffering from metal pollution such as mercury. Hizikia fusiformis is a commercially important brown marine macroalga. Entire thalli of H. fusiformis were cultured in media with different mercury concentrations for 7 days to examine the physiological effects of mercury exposure on this species. The relative growth rate of H. fusiformis was significantly reduced at 0.04 mg l-1 mercury. Chlorophyll a and carotenoid contents were not affected by mercury concentrations ≤0.10 mg l-1, but significantly decreased at 0.20 and 0.40 mg l-1. Optimal quantum yield, maximum net photosynthetic rate, and apparent photosynthetic efficiency were reduced with increasing mercury concentrations. Malondialdehyde contents were significantly increased at 0.04–0.40 mg l-1 mercury. Superoxide dismutase activity increased at 0.02–0.10 mg l-1 mercury. Both superoxide dismutase and catalase activity strongly decreased at 0.20 and 0.40 mg l-1. Nitrate reductase activity declined at mercury concentrations ≥0.04 mg l-1. Consequently, the results suggest that H. fusiformis could tolerate mercury stress at very low concentrations but that mercury at high concentrations has toxic effects on H. fusiformis through its negative influence on photosynthesis and related physiology. The results also illuminate the physiological response mechanisms of algae to mercury exposure.