The influence of salinity and copper exposure on copper accumulation and physiological impairment in the sea anemone, Exaiptasia pallida

Copper is a common pollutant in many aquatic environments, particularly those surrounding densely populated areas with substantial anthropogenic inputs. These same areas may also experience changes in salinity due to freshwater discharge and tidal influence. Biota that inhabit near-shore coastal environments may be susceptible to both stressors. Although copper is a noted concern in marine environments, effects of copper and varying salinity on symbiotic cnidarians are only scarcely studied. The sea anemone, Exaiptasia pallida, was used to investigate effects of copper on physiological impairment (i.e. activities of anti-oxidant enzymes) at two different salinities (20 and 25 ppt). E. pallida was exposed to a control and three elevated copper concentrations for up to 21 d, and copper accumulation and activity of the enzymes: catalase, glutathione reductase, glutathione peroxidase, and carbonic anhydrase were measured in the anemones. Photosynthetic parameters in E. pallida's symbiotic dinoflagellate algae were also quantified. Over the course of the exposure, E. pallida accumulated copper in a concentration-dependent manner. Higher tissue copper concentrations were observed in anemones exposed to the lower salinity water (20 ppt), and physiological impairment was observed as a consequence of both increased copper exposure and decreased salinity; however, changes in salinity caused a greater response than copper exposure, at the levels tested. In general, antioxidant enzyme activity increased as a consequence of decreased salinity and/or increased copper exposure. These results clearly demonstrated the influence of two local stressors, at environmentally realistic concentrations, on a sensitive cnidarian, and highlight the importance of characterizing combined exposure scenarios.