The toxicological interaction between ocean acidity and metals in coastal meiobenthic copepods

Increased atmospheric CO₂ concentrations are causing greater dissolution of CO₂ into seawater, and are ultimately responsible for today’s ongoing ocean acidification. We manipulated seawater acidity by addition of HCl and by increasing CO₂ concentration and observed that two coastal harpacticoid copepods, Amphiascoides atopus and Schizopera knabeni were both more sensitive to increased acidity when generated by CO₂. The present study indicates that copepods living in environments more prone to hypercapnia, such as mudflats where S. knabeni lives, may be less sensitive to future acidification. Ocean acidification is also expected to alter the toxicity of waterborne metals by influencing their speciation in seawater. CO₂ enrichment did not affect the free-ion concentration of Cd but did increase the free-ion concentration of Cu. Antagonistic toxicities were observed between CO₂ with Cd, Cu and Cu free-ion in A. atopus. This interaction could be due to a competition for H⁺ and metals for binding sites.