The distribution and abundance of the invasive ctenophore Mnemiopsis leidyi in the Bornholm Basin, an important spawning ground of several fish stocks, and in adjacent areas in the central Baltic Sea was studied in November 2007. The study showed that M. leidyi were relatively small (body length 18.6 ± 7.6 mm) and they were patchily distributed over a large part of the investigated area. Specimens were found on 68 and 59% of stations sampled with a Bongo net (n=39) and an Isaac-Kidd midwater trawl (n=51), respectively. Vertically, the highest densities of M. leidyi occurred at 40 to 60 m around the halocline. Horizontally, the highest abundances were found north and west of Bornholm, but relatively high densities were also observed in the Slupsk Furrow. The mean abundance was 1.58 ± 2.12 ind. m -2 , the peak abundance was 8.92 ind. m -2 , and the average and peak population density were 0.03 ± 0.05 and 0.28 ind. m -3 , respectively. The abundances are low compared to densities recently observed in other areas of the Baltic region (e. g. Limfjorden, Åland Sea) and the estimated predation impact on zooplankton by M. leidyi was negligible in November 2007. However, because of the ctenophore's wide distribution in the central Baltic Sea, its ability for rapid population growth, and its potential influence on fish stocks by competing for food and by preying on fish eggs and newly hatched larvae, close monitoring of the future development of M. leidyi in the Baltic Sea is strongly recommended.

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The invasive ctenophore, Mnemiopsis leidyi, which had its first mass occurrence in Limfjorden (Denmark) . During that period, copepods and other mesozooplankton organisms were virtually absent while ciliates were a substantial part of the zooplankton biomass. In "pre-Mnemiopsis years", there seems to have been large variability in the grazing impact on zooplankton depending on the seasonal abundance of A. aurita. With the addition of the second carnivore M. leidyi, however, additional predation pressure caused the zooplankton stocks to be severely depressed throughout 2008 and 2009 when copepods and cladocerans no longer showed the high seasonal peaks in abundance typical of previous years.

Resumen Una especie nueva del género Streblospio Webster, 1879 (Annelida, Spionidae) ha sido identificada en el sureste del golfo de Vizcaya. La nueva especie, Streblospio eunateae sp. nov., ha sido recolectada entre los años 2013 y 2018 en sedimentos fangosos intermareales y submareales de las provincias de Gipuzkoa y Bizkaia (NE de la península Ibérica). Se realiza una descripción, ilustración y discusión de la misma, aportándose también información sobre su ecología y distribución. Complementariamente, se aporta una clave de identificación de todas las especies conocidas de Streblospio. Abstract A new species of the genus Streblospio Webster, 1879 (Annelida, Spionidae) has been identified from SE Bay of Biscay. The new species, Streblospio eunateae sp. nov., has been collected between 2013 and 2018 in intertidal and sub-littoral muddy sediments from Gipuzkoa and Bizkaia (NE Iberian Peninsula). The species is described, illustrated and discussed. Some notes on its ecology and distribution in the area is also included. In addition, an identification key is provided for all known Streblospio species.

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