The meltdown of biogeographical peculiarities of the Baltic Sea: the interaction of natural and man-made processes.

The biogeographical peculiarities of the Baltic Sea have developed since the last glacial period. The characteristic mixture of marine, brackish water, and freshwater species, and relicts from previous periods in the Baltic, is threatened by ongoing environmental changes. This review focuses on the recent impacts of nonindigenous species, eutrophication, and a temporary oxygen deficit in the deep basins, on the biogeographical integrity of the Baltic on different spatial and time scales. Today the biota of brackish waterbodies are exposed to each other because of the breakdown in geographical barriers due to shipping traffic, leading to an exchange of species and further homogenization of aquatic animal and plant life worldwide.