Performance of mussel Mytilus galloprovincialis under variable environmental conditions and anthropogenic pressure: A survey of two distinct farming sites in the Adriatic Sea.

Changes in natural conditions and anthropogenic pollutants, alone or in combination, pose a significant challenge to coastal bivalve populations. The susceptibility of economically important bivalves to potential stressors in their farming environment has not been sufficiently investigated, despite the increase in anthropogenic pressure along the coast and the remarkable warming of seawater in recent years. Thus, the aim of this study was to evaluate the performance of mussel (Mytilus galloprovincialis) from two important farming sites in the eastern Adriatic, namely Mali Ston Bay (MSB) and Lim Bay (LB), in relation to variations of seawater parameters, reproductive cycle dynamics and tissue content of potentially harmful pollutants. The complex seasonal and site-specific patterns of chemical pollutants were determined, with tissue levels of metals, As, PAHs and PCBs largely comparable to those previously reported for the Mediterranean region. Concentrations of organochlorinated pesticides were below the level of detection. Significantly higher Cd, As and Hg concentrations were detected in the tissues of the MSB mussels. The reproductive cycle was clearly associated with the bioaccumulation of pollutants. All biochemical response parameters varied to some extent across seasons and/or between farming sites. A very pronounced seasonality was recorded for acetylcholinesterase and glutathione S-transferase activity at both sites. Metallothionein concentration and superoxide dismutase activity were generally steady throughout the study period. The most striking difference between the two sites was recorded for lipid peroxides concentrations which were predominantly significantly higher in the MSB mussels, indicating expressed pro-oxidant conditions at this site. In particular, significant correlations were found between lipid peroxides and the potentially toxic metals (Cd, As, Hg) accumulated in the mussel tissue. Data reported here are valuable as baseline information for further studies related to stress in farmed bivalves caused by oscillations of environmental factors and increasing anthropogenic pressure along the coastline.