A new predatory cladoceran Cercopagis (Cercopagis) pengoi (Ostroumov 1891) in the Gulf of Gdańsk

Cercopagis pengoi, a species native to the Ponto-Caspian area, was recorded for the first time in the Baltic Sea in the Gulf of Riga and in the open Gulf of Finland in 1992. Sampling in the shallow coastal area of the western part of the Gulf of Gdańsk at weekly intervals between April 1999 and April 2000 revealed the presence of C. pengoi in the zooplankton community. The species was recorded twice, at densities of 1369 indiv. m−3 on 30 July 1999 and 421 indiv. m−3 on 5 August 1999, when the water temperature was at its maximum, in excess of 21.7◦C and 23.9◦C respectively. C. pengoi had never been recorded in the Gulf of Gdańsk prior to 1999.