Climatic changes and anthropogenic impact have resulted in numerous cases of introduction and range expansion of hydrobionts. In the late 20th century and in the early 21st century some species, previously not observed in the Vistula and Curonian lagoons (brackish waterbodies with well-developed port infrastructure and active navigation) were recorded more than once in the study area. The aim of this study was to characterize cases of alien polychaete introductions in the Russian part of the South-Eastern Baltic Sea, including shallow lagoons. Samples of zoobenthos, collected in the Russian exclusive economic zone in the South-Eastern Baltic Sea (139 sampling sites, 2001–2016), the North-Eastern Vistula Lagoon (45 s. s., 1997–2016) and the Southern Curonian Lagoon (24 s. s., 2001–2016), were studied. The material is stored in the IO RAS zoological collection. The south-western (Polish) part of the Vistula Lagoon and the northern (Lithuanian) part of the Curonian Lagoon were characterized using previously published data. In the Vistula Lagoon since the 1880s for over a century polychaetes were represented by the only species – Hediste diversicolor. Since the end of the 20th century, new species for the region have been registered: Marenzelleria neglecta (since 1988); Streblospio benedicti, Manayunkia aestuarina, Alkmaria romijni (since middle 1990s); Boccardiella ligerica (since 2008 in the Polish waters and since 2013 in the Russian waters); Laonome cf. calida (since 2014). In the Curonian Lagoon polychaetes (the only species, M. neglecta) occur in the northern (Lithuanian) part only. In the Russian part of the South-Eastern Baltic polychaetes of Marenzelleria genus have been registered since 1988, while M. arctia – since 2001, S. benedicti and B. ligerica have been recorded since the beginning of the 21st century. Thus, in the marine waters of the South-Eastern Baltic, three alien polychaete species have been recorded, while in the Vistula Lagoon – five, and in the Curonian Lagoon – one species. These introduced species belong to a group of estuarine, brackishwater infaunal organisms, whose native areals are in the Western or Eastern Atlantic and the south-western part of the Pacific Ocean. Salinity conditions have been shown to be the most favorable for aliens in the marine part of the study area, while trophic conditions – in the lagoons. The optimal combination of environmental factors for the aliens has been found to be in the shallow Vistula Lagoon due to an existence of the aria with bottom salinity not lower then 3.7–5.9 ‰, predominance of soft silty sediments, abundance of organic matter, and insignificant competition for food resources. Information on distribution, occurrence, abundance and status of alien populations is given.
Remote Sensing of Coastal Upwelling in the South-Eastern Baltic Sea: Statistical Properties and Implications for the Coastal Environment