Role of lipids and fatty acids (FA) in littorial and sublittorial White Sea mussels Mytilus edulis L. was studied at various stages of reproductive in the phenotypic adaptation (acclimation) to changes of the sea water salinity. The obtained data indicate differences in the mussel lipid and fatty acid spectra, which are connected both with their location (littoral and sublittoral) and with the spawning period stage (3b--release of gametes and 3c--resorption of residual sex products). Lipids and FA of both mussel groups respond to the salinity changes to the greater degree at the 3b than at the 3c stage. In the littorial mussels at the stages 3b and 3c there were revealed differently directed changes in the content of membrane lipid--cholesterol--and in the cholesterol : phospholipids ratio. In the sublittorial mussels that are less adapted to extreme action of abiotic factors, more significant changes were found in the lipid and FA compositions.