Ref ID : 6657
Goran Milbrink; Distribution and dispersal capacity of the Ponto-Caspian tubificid oligochaete Potamothrix heuscheri (Bretscher, 1900) in Scandinavia. Hydrobiologia 406:133-142, 1999
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The species composition of the Scandinavian freshwater oligochaete fauna is strongly influenced by its post-glacial history (Timm, 1980). Few species are likely to have survived in the core areas of glaciation and the present composition of species has thus been highly dependent upon the immigration rate of 'new' species (Milbrink, 1980). Active immigration into new localities has proven to be a very slow process, whereas passive transportation in running water and by rafting is much faster. Exchange of ballast water in harbours is likely to be the single most effective action by man, causing large-scale passive dispersal of the aquatic fauna and flora. Bottom water with stirred-up sediment containing oligochaetes could thereby be sucked into the tanks of ships and later exchanged in nearby and distant ports. Ponto-Caspian species among the Tubificidae, originating in the Black Sea-Caspian Sea region, are continuously dispersing to the west over Central Europe and to be north-west towards the Baltic Sea area (Timm 1970, 1980; Milbrink 1980) adding to the species list of the Tubificidae. Five such species of the genus Potamothrix have quite recently reached eastern Sweden (Milbrink, 1980). The dispersal front presently goes obliquely across Scandinavia from the north-east to the south-west. Comparisons with results from previous bottom-sampling series in Lake Malaren from 1915 to 1916 revealed ongoing colonization, especially in those basins of the lake which were in recent contact with the Baltic Sea and thus had brackish bottom water. One of those species, Potamothrix heuscheri, which is particularly tolerant to anoxic conditions and high salinity and is likely to have reached Scandinavia in ballast water possibly via indirect sources from the Mediterranean Sea. Its uneven distribution in Scandinavia is well correlated with historic water-ways for heavy transport, for instance via cargoes of wood pulp from Lake Munksjon to the south of Lake Vattern and to and from other cellulose industries on the Baltic coast. It is speculated that distant occurrences of P. heuscheri in Africa and South America may have been reached through passive transport in the plumage of migrating wading-birds.