Stakowian_2025_Comp.Biochem.Physiol.A.Mol.Integr.Physiol__111954

Environmental salinity is one of the main factors causing osmotic stress in coastal bivalves, influencing their physiological performance and distribution. The Mediterranean mussel Mytilus galloprovincialis is one of the most euryhaline marine invertebrates, tolerating large salinity fluctuations throughout its wide geographical distribution. This study investigated how different tissues respond to different salinities, identifying potential biochemical markers of tolerance and plasticity. Mussels were exposed for 14 and 28 days to the salinities 20, 25, 30, 35, and 40, and biomarkers related to metabolism, antioxidant and biotransformation systems, cellular damage, and neurotoxicity were analyzed in the digestive gland, gills, mantle, and muscle. The digestive gland showed significant modulation of succinate dehydrogenase, glycogen, superoxide dismutase, antioxidant capacity, and carboxylesterase activity, demonstrating its metabolic and antioxidant role. The gills showed changes in glutathione S-transferase, acetylcholinesterase, and lipid peroxidation levels, particularly under hyposaline (20) and hypersaline (40) conditions. Mantle and muscle showed lower responsiveness to the tested salinities. Biochemical responses at salinities between 25 and 35 indicated the activation of allostatic mechanisms assuring survival and damage prevention. The results corroborate the concept of salinity-induced allostasis as a mechanism of resistance in osmoconforming euryhaline bivalves. Furthermore, they highlight the importance of functional compartmentalization among tissues in responding to osmotic challenges. The results also support the use of organ-level biomarkers to assess physiological resistance to salinity gradients in coastal environments.