The round goby (Neogobius melanostomus) in the Gulf of Gdansk -: a species introduction into the Baltic Sea

In recent years, information concerning the awareness of organisms accidentally introduced into the Baltic Sea has substantially improved. Non-indigenous Estuarine and Marine Organisms (NEMO's) are hazardous for the Baltic ecosystem. Currently, about one hundred species are identified as accidentally or intentionally introduced into the Baltic Sea. Ballast waters and escape from aquaculture are the most important invasion vectors. During the last decade, an invasion of the round goby (Neogobius rnelanostomus) - a Ponto-Caspian fish species has been observed in the Gulf of Gdansk. The first record of this fish in the Baltic Sea is from 1990. Early detection of the invader enabled the study of population growth and changes in the area. The first years of invasion were characterized by low numbers of individuals and a limited distribution. Later, the round goby gradually colonized all shallow waters in the western part of the Gulf of Gdansk. Initially the fish inhabited stony and rocky habitats, but later it also occupied sandy bottoms. The round goby is now the dominating fish species in most of the shallow waters of the Gulf of Gdansk. Two main factors account for the successful invasion of this fish in the region: the state of ecosystem at the time of the invasion and the biological features of N. melanostomus. In the late 1980s, the shallow waters of the Gulf of Gdansk were almost devoid of piscivorous fishes. Concurrently, bivalves (a preferred prey of the round goby) have increased. Important is also parental care of laid eggs and reproductive strategy. Population growth potential enables the colonization of nearby regions. The first round gobies in the Vistula Lagoon were collected in 1999 and colonization of other Baltic Sea areas is anticipated.