Influence of salinity and organic matter on the toxicity of Cu to a brackish water and marine clone of the red macroalga Ceramium tenuicorne.

Cu is a major active component in anti-fouling paints, which may reach toxic levels in areas with intense boat traffic and therefore is a metal of environmental concern. The bioavailability of metals is influenced by factors such as salinity and organic matter measured as total organic carbon (TOC). The influence of these two factors was studied, with a focus on brackish water conditions, by exposing a marine and a brackish water clone of the red macroalga Ceramium tenuicorne to Cu in different combinations of artificial seawater (salinity 5-15‰) and TOC (0-4 mg/L) in the form of fulvic acid (FA). In addition, the toxicity of Cu to both clones was compared in salinity 10‰ and 15‰. The results show that by increasing TOC from 0 to 2 and 4 mg/L, Cu was in general less toxic to both algal clones at all salinities tested (p<0.05). The effect of salinity on Cu toxicity was not as apparent, both a positive and negative effect was observed. The brackish water clone showed generally to be more sensitive to Cu in salinity 10‰ and 15‰ than the marine counterpart. In conclusion, FA reduced the Cu toxicity overall. The Cu tolerance of both strains at different salinities may reflect their origin and their adaptations to marine and brackish water.