Finland’s environmental administration asks people to inform the authorities about their observations on alien species. In the Baltic Sea, that is.
With more information on the species the authorities can plan the steps needed to be taken, if there are any. To make it as easy as possible, there is even a form on the net one can fill in in case of an alien observation. As far as I could find out, the form was only in Finnish. There are quite a few Swedish speaking citizens living on the coast, with a large knowlegde of the sea and it’s life. I hope they find their way to the form too.
Further information about the alien species in the Baltic Sea one can find on the Baltic Sea Alien Species Database