|The Baltic Sea, including Bothnian Sea and Bothnian Bay|
Kautsky, L.; Kautsky, N. (2000). The Baltic Sea, including Bothnian Sea and Bothnian Bay, in: Sheppard, C.R.C. (Ed.) Seas at the millennium: an environmental evaluation: 1. Regional chapters: Europe, The Americas and West Africa. pp. 121-133
In: Sheppard, C.R.C. (Ed.) (2000). Seas at the millennium: an environmental evaluation: 1. Regional chapters: Europe, The Americas and West Africa. Pergamon: Amsterdam. ISBN 0-08-043207-7. XXI, 934 pp., more
|Authors|| || Top |
The Baltic Sea region is one of the largest brackish water areas in the world with a salinity declining from about 10 PSU in the south in the Baltic Proper, declining through the Bothnian Sea to 2 PSU in the northern Bothnian Bay. It is surrounded by 14 densely populated and industrialised countries, where 90 million people live within the drainage area. The narrow and shallow Danish straits limit the water exchange and result in a residence time of the water of 25-30 years. The north-south salinity gradient restricts the northward penetration of marine organisms, and the few which do occur in the north often show dwarfism. A permanent halocline at about 60-80 m depth prevents vertical circulation, and oxygenation of the deep water is limited to a few events of salt-water inflow. About one third of the bottom area of the Baltic Proper is devoid of higher life due to low oxygen. The Baltic Sea has no tides. The hard bottoms are dominated by communities of Fucus vesiculosus and Mytilus edulis, and some further 30 species. Soft-bottom communities are dominated by the bivalve Macoma balthica and three more species in the Baltic Proper, but both biomass and number of species decrease rapidly to the north. Production of pelagic fish like herring and sprat is high, but benthic species like cod and flounder are declining due to eutrophication. There is also a significant fishery of freshwater fish such as pike and perch in the coastal areas. The pollution load is high, affecting e.g. reproduction of top carnivores, although species such as seals and white-tailed sea eagle, which were threatened by DDT and PCB levels until recently, are now recovering. The main problem is eutrophication, favouring growth of nuisance algae, and a lowering of oxygen in the benthos. Since most organisms of this region are already living under severe physiological stress, they are sensitive to pollution, and the low number of species increases the risk that whole functional groups can be lost.