Responses of the sea anemone, Exaiptasia pallida, to ocean acidification conditions and copper exposure

Ocean acidification (OA) is a growing concern due to its deleterious effects on aquatic organisms. Additionally, the combined effects of OA and other local stressors like metal pollution are largely unknown. In this study, we examined physiological effects in the sea anemone, Exaiptasia pallida after exposure to the global stressor carbon dioxide (CO2), as well as the local stressor copper (Cu) over 7 days. Cu accumulated in the tissues of E. pallida in a concentration-dependent manner. At some time points, sea anemones exposed to 1000 ppm CO2 had higher tissue Cu concentrations than those exposed to 400 ppm CO2 at the same Cu exposure concentrations. In general, the activities of all anti-oxidant enzymes measured (catalase, CAT; glutathione peroxidase, GPx, glutathione reductase, GR) increased with exposure to increasing Cu concentrations. Significant differences in GR, CAT and to some degree GPx activity, were observed due to increasing CO2 exposure in control treatments. Sea anemones exposed to Cu in combination with higher CO2 generally had higher anti-oxidant enzyme activities than those exposed to the same concentration of Cu and lower CO2. Activity of the enzyme, carbonic anhydrase (CA), involved in acid-base balance, was significantly decreased with increasing Cu exposure. At the two lowest Cu concentrations, the extent of CA inhibition was lessened with increasing CO2 concentration. These results provide insight into toxic mechanisms of both Cu and CO2 exposure to the sensitive cnidarian E. pallida and have implications for environmental exposure of multiple contaminants.