Abstract
The invasive ctenophore Mnemiopsis leidyi is expanding its range in the Baltic Sea. It was observed in the Landsort Deep in March 2007 and in the western part of the Gulf of Finland, Aland and Bothnian Seas in August 2007. In September the abundances were several times higher in the Gulf of Finland and the Aland Sea than in August, maximum abundances being 694 ind m -2 , and densities 24 ind m -3 . In December M. leidyi was observed also in the eastern Gulf of Finland at low abundances. Eggs and newly hatched larvae as well as juvenile stages were observed during autumn, indicating efficient reproduction and establishment of the species in the northern Baltic Sea.
Highlights
Aquatic invasive species (AIS) have been identified globally as one of the major threats to marine ecosystems, causing biodiversity loss and adverse environmental, economic and social impacts (Leppäkoski et al 2002b)
M. leidyi has been unintentionally introduced with ballast water to the Black Sea in 1982 (Vinogradov et al 1989) and later, in 1999, to the Caspian Sea (Ivanov et al 2000)
The samples were taken by vertical hauls using a WP-2 net from the bottom to the halocline and from the halocline to the surface, according to the temperature and salinity profiles measured by CTD casts at each sampling site
Summary
Aquatic invasive species (AIS) have been identified globally as one of the major threats to marine ecosystems, causing biodiversity loss and adverse environmental, economic and social impacts (Leppäkoski et al 2002b). M. leidyi was able to overwinter in low abundances (1-4 ind m-3) in the southern Baltic at temperatures below 10 oC (Kube et al 2007). We report on the further spread of M. leidyi from the central to the northern Baltic Sea during spring, summer and autumn 2007.
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