How are the zebra mussels doing in the Gulf of Finland?

The zebra mussel (Dreissena polymorpha) was first found in the Gulf of Finland only in 1990. Its distribution, abundance, ecology, and growth rate were studied in this area using SCUBA diving. The growth rate of juveniles and adults was studied by direct observations in the nature on artificial substrates and by reconstructing the linear growth from annual rings. Growth rate analysis was performed for five local populations dispersed widely in both the Finnish and Russian parts of the Gulf of Finland. It was found that the dispersal of zebra mussels to the west of the gulf is limited by the average salinity level of 5 PSU. During the last decade, the abundance of the mussels increased from one to two orders of magnitude. The growth rate of the zebra mussels in the Gulf of Finland is probably the lowest worldwide.