Marine midge Telmatogeton japonicus Tokunaga (Diptera: Chironomidae) exploiting brackish water in Finland

Pupal exuviae of marine intertidal midge Telmatogeton japonicus Tokunaga (Diptera: Chironomidae) were found in September 2008 from the Gulf of Finland, Baltic Sea. Previous records of the species in the Baltic Sea were from Sweden, Denmark, Germany and Poland. Telmatogeton japonicus is an alien species introduced to Europe from the Pacific Ocean. It probably uses shipping as the vector, since in north-western Europe it has first been detected near large seaports. This was also the case in the Gulf of Finland. Our findings suggests that the species' distribution extends further northeast in the Baltic Sea than understood before, and that the species is able to establish viable populations into fresh-brackish (salinity < 4 ‰) coastal habitats.