First attempts at evaluating combined effects of pH, temperature and salinity on haemocyte responses of the mussel Mytilus galloprovincialis

The increment of atmospheric concentration of CO2 is responsible for both global warming and acidification of oceans. Although ocean acidification may negatively affect all organisms, modifying their development, growth, physiological activities and metabolic rates, calcifying ones are recognized as the most vulnerable, due to possible reduction occurring in calcification rate. In the frame of the Circle-Med Project aimed at evaluating impacts of marine acidification, temperature and precipitation changes on physiological responses and shell structure of bivalves, alterations in immune functions of the mussel Mytilus galloprovincialis have been investigated. Adult mussels were exposed for 7 days in a through-flow system to three pH values (8.1, 7.7 and 7.4), each at two temperatures (22 and 28°C). Experiments were carried out at 28, 34 and 40 PSU salinity, respectively. Combined effects of the above parameters (8.1 pH, 22°C and 34 PSU as reference values) were evaluated on total haemocyte count (THC), haemocyte endocytotic activity and haemolymph lysozyme-like activity. Although increasing THC values with increasing temperature were generally observed, significant reduction was found at lowest pH values and the highest salinity. For all salinities tested, the highest endocytotic activity was found at 8.1 pH, the lowest at 7.4 pH. Lysozyme activity increases at 8.1 and 7.4 pH values combined with higher temperature, except for 7.4 pH at 40 PSU. Overall, immune responses of M. galloprovincialis showed to be mostly affected by the combination of low pH and high salinity values, suggesting increased stress conditions and impaired immune defense against pathogens. Acknowledgement - This work was funded by IMELS in the frame of the European CIRCLE-MED Project, ACIDBIV