The Ponto-Caspian invader Evadne anonyx Sars (Crustacea, Cladocera) in the pelagic zone of the Southeastern Baltic

The Ponto-Caspian cladoceran Evadne anonyx (G.O. Sars, 1897) was recorded in the summer zooplankton of the Southeastern Baltic (SEB) in 2010–2011. The quantitative parameters of the species were low. The share of the introduced species in the total abundance and biomass of zooplankton was not significant. The population of E. anonyx was represented predominantly by parthenogenetic females with 1–22 eggs. Among individuals, males were found and that allowed the suggestion of the presence of sexual reproduction and formation of gamogenetic eggs in the populations of E. anonyx in the SEB. Morphometric parameters of populations of E. anonyx and fertility of parthenogenetic females in the SEB were comparable with those of Caspian forms. It is possible that, with the emergence of the new species E. anonyx, structural and functional changes may take place in zooplankton community of half-closed Curonian and Vistula lagoons of the Baltic Sea.

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