Successful establishment of the Ponto-Caspian alien cladoceran Evadne anonyx G.O. Sars 1897 in low-salinity environment in the Baltic Sea

摘要

Our new results confirm that the Ponto-Caspian cladoceran Evadne anonyx was first found in the Gulf of Finland in 1999. In the Gulf of Riga, the first specimens were detected in 2000. The observed distribution pattern, together with the recorded increase in the population density of the species of ca. 10 times during the years 2000–2006 indicate the recent successful establishment of E. anonyx in the low-salinity conditions (<5 psu) of the NE Baltic Sea. Evadne anonyx and the native E. nordmanni are present in mesozooplankton community from May to October. In the seasonal cycle, the maximum abundance of E. anonyx may occur later in the season than that of E. nordmanni. As the fecundity of the alien E. anonyx significantly exceeds that of the native E. nordmanni, we suggest that population abundance of E. anonyx will very likely increase in future and the species may colonize new areas in the recently invaded ecosystem.