Blue mussels M. edulis(Me) and M. trossulus(Mt) form mixedpopulations and hybrid zones in the North Atlantics. Dynamic of these systems are poorly understood. Mussels exhibit two discrete morphs: T-morphotype (Tm, underdevelopment nacreous layer under the ligament nympha) and E-morphotype (Em, nacreous layer iswell developed). We investigated the association between morphotype and species genotype in the White Sea and revealed that mussels with Tm are mostly Mt whereas mussels with Em -Me. We further analyzed current (2013-2018) distribution of morphotypes along the Gulf of Kandalaksha and inspected old collections from the area, in particular annual samples from four monitoring sites in Kandalaksha harbor area obtained through 2002-2018.Populations with high concentration of Tm were from areas associated withactive or abandoned sea ports. Mussels with Tm were rare in collections sampled before 2000. Rapid rise in Tm frequencies in populations of Kandalaksha harbor area happened between 2002 and 2014. However, Tm frequencies experienced some decreasing thereinlast years.High concentration of Tm in areas associated with sea ports is in a good agreement with the hypothesis of introduction of Mt into the White Sea by oceanic transport. Rapid expansion of Tm around Kandalaksha harbor in the very beginning of the century we relate to the massive freshwater discharge from local hydroelectric power plant in 2000, which was catastrophic for marine intertidal communities. After the extinction of intertidal mussel populations, the areas were colonized by more opportunistic Mt. Recent decline in Tm frequencies we relate to competitive exclusion of Mt by Me in more stable hydrological situation in the area in last years.The research was supported by RSF (project No. 19-74-20024)