Abstract
The use of temperate species to assess the risk of chemical toxicity to Arctic species may be difficult, because different temperatures and differences in organism lipid content affect uptake/depuration kinetics and the subsequent toxic responses. There have so far only been a few attempts to determine whether temperate effect levels are in fact applicable to polar biota. In order to address these issues we conducted a comparative study using two closely related calanoid copepod species; Calanus finmarchicus and Calanus glacialis. C. finmarchicus is considered an Atlantic copepod, whereas the C. glacialis is considered an Arctic copepod, and the experiments on C. finmarchicus and C. glacialis were conducted at relevant temperatures for the two species; 8°C and 2°C, respectively. Copepods were exposed to either inorganic (ionic mercury) or organic (water-soluble fraction of a weathered crude oil) contaminants in three differently designed acute experiments. Firstly, LC50 levels for both contaminants were determined for both species. Secondly, experiments were conducted applying sub-lethal exposures at three different concentrations to both species followed by sampling after 12, 24 and 48 hrs. Sampled copepods were analyzed for expression of stress genes (e.g. glutathione S-transferase). Finally, we conducted experiments to determine uptake of mercury during acute exposure, and experiments revealing the relationship between lipid content and acute toxicity to WSF exposure. Clear differences were shown in terms of acute toxicity between the two different stressors, and mercury was vastly more toxic than WSF in terms of LC50. In addition, mercury was equally toxic to both species, whereas WSF was more toxic to the Atlantic copepod. This may be attributed to differences in temperature optimum and lipid content of the two species. Investigations of metal uptake reveal a similar uptake rate in line with the results from the LC50 tests. For WSF, a suspected lipid content-de