Immunomodulating effects of environmentally realistic copper concentrations in Mytilus edulis adapted to naturally low salinities.

The possibility to assess organisms’ health condition and biological effects of chemicals is a fundamental requirement for the achievement of the Good Environmental Status (GES) as defined in the Marine Strategy Framework Directive (EU). In this respect, the role of natural environmental stressors, possibly acting as confounding factors, should be carefully considered, especially at low doses of exposure. Organisms from the Baltic Sea have adapted to the ambient salinity regime, however energetically costly osmoregulating processes may have an impact on the capability to respond to additional stress such as contamination. In the present study, immune responses of Mytilus spp, adapted to salinities of 12 ‰ (LS) and 20 ‰ (MS) were compared after short-term exposure (1, 7 and 13 days) to low copper concentrations (5, 9 and 16 µg/L Cu). In brief, LS mussels accumulated markedly more copper than MS mussels, and exhibited a strong correlation between bacterial clearance and phagocytic activity. The greatest separating factor of LS and MS was the proportion of granulocytes and hyalinocytes while functional parameters (phagocytic activity and bacterial clearance) were merely affected by salinity, but rather by copper exposure. The overall results demonstrated that immune responses may be suitable biomarkers for the assessment of ecosystem health in brackish waters (10 to 20 ‰ S), and that the impact of salinity on physiological processes should be accounted for

Effects of various pollutant mixtures on immune responses of the blue mussel (Mytilus edulis) collected at a salinity gradient in Danish coastal waters

The Baltic Sea is a semi-enclosed sea with a steady salinity gradient (3‰–30‰). Organisms have adapted to such low salinities, but are suspected to be more susceptible to stress. Within the frame of the integrated environmental monitoring BONUS + project “BEAST” the applicability of immune responses of the blue mussel was investigated in Danish coastal waters. The sampling sites were characterised by a salinity range (11–19‰) and different mixtures of contaminants (metals, PAHs and POPs), according to chemical analysis of mussel tissues. Variation partitioning (redundancy analysis) was applied to decompose salinity and contamination effects. The results indicated that cellular immune responses (total and differential haemocyte count, phagocytic activity and apoptosis) were mainly influenced by contaminants, whereas humoral factors (haemolytic activity) were mainly impacted by salinity. Hence, cellular immune functions may be suitable as biomarkers in monitoring programmes for the Baltic Sea and other geographic regions with salinity variances of the studied range