Round goby Neogobius melanostomus in the Baltic Sea – Invasion Biology in practice

Abstract: Human mediated transfer of non-indigenous species is considered to be a major threat to global biodiversity. The Ponto-Caspian round goby (Neogobius melanostomus), which has established populations in various regions in Eurasia and North-America, was first observed in Gulf of Gda?sk, Baltic Sea, in 1990. In this thesis the round goby is used as case study for assessing the invasion process of an alien species in to the Baltic Sea. Factors governing life history characteristics, traits that have enhanced the invasion, and ecological consequences for the Baltic Sea are assessed. Two diverging life history strategies of the round goby related to habitat were found: one to-wards early maturation and short population turnover time in sheltered areas, the other towards high growth rate and late maturation in exposed areas. Females produced two batches in average during the spawning season. Lengths of spawning season and annual fecundity of round gobies in Gulf of Gda?sk were in the same range as in the donor region. The species was found to compete with juvenile flounder for space and food resources, and probably also other native species are affected in coastal areas. Round goby comprised a main food source for cod and perch, forming a new energetic pathway between mussels and predatory fish. It is predicted that the species must produce more than one batch per season to sustain a viable population. Low temperature in the northern Baltic Sea is expected to hamper the devel-opment of new round goby populations, however, the global climate change might change this situation. In the southern Baltic Sea a shortage of optimal reproduction habitats is suggested to moderate the rate of spread. Although round goby in the Gulf of Gda?sk seems to have passed abundance maximum it is likely that the species will continue to be an important ecosystem component, at least in southern Baltic Sea, in the future.