Changes of the lipid composition (mainly of membrane lipids) in gills in response to various seawater salinities were studied in two groups of mussels Mytilus edulis L. from the White Sea, living under different environmental conditions (intertidal zone and artificial substrates used in aquaculture). Modifications in the lipid composition involved the basic indices characteristic of the physical state of biological membranes, and minor components of the lipid bilayer, which perform regulatory functions, indicating that the lipid metabolism of the bivalves has undergone acclimation transformations in response to salinity. It is demonstrated that the response to critical salinity (5 ppt) in membrane lipids was similar in the two investigated groups of mussels, whereas with salinities of 15, 35, and 45 ppt the pattern of fluctuations in the lipid composition depended on the initial habitat (intertidal zone or aquaculture).

Alterations of membrane lipid composition (cholesterol, phospholipids and their fatty acids) in response to various temperature changes were studied in blue mussels Mytilus edulis L. from the White Sea. Lipid composition changes after acute temperature stress, especially a temperature drop, included a significant reduction of the membrane phospholipid content directly (1 h) after return to the initial temperature, which was presumably a consequence of a non-specific stress reaction in the mussels. A longer recovery period (24 h) as well as long-term temperature acclimation (14 days) induced changes in gill fatty acid composition (for instance, a rise in phospholipid unsaturated fatty acids under low temperature impact), indicating ‘homeoviscous adaptation’ to maintain the membranes in response to temperature fluctuations. Moreover, the gill cholesterol level in mussels varied especially at long-term temperature exposure.