Status of Biodiversity in the Baltic Sea

The brackish Baltic Sea hosts species of various origins and environmental tolerances. These immigrated to the sea 10,000 to 15,000 years ago or have been introduced to the area over the relatively recent history of the system. The Baltic Sea has only one known endemic species. While information on some abiotic parameters extends back as long as five centuries and first quantitative snapshot data on biota (on exploited fish populations) originate generally from the same time, international coordination of research began in the early twentieth century. Continuous, annual Baltic Sea-wide long-term datasets on several organism groups (plankton, benthos, fish) are generally available since the mid-1950s. Based on a variety of available data sources (published papers, reports, grey literature, unpublished data), the Baltic Sea, incl. Kattegat, hosts altogether at least 6,065 species, including at least 1,700 phytoplankton, 442 phytobenthos, at least 1,199 zooplankton, at least 569 meiozoobenthos, 1,476 macrozoobenthos, at least 380 vertebrate parasites, about 200 fish, 3 seal, and 83 bird species. In general, but not in all organism groups, high sub-regional total species richness is associated with elevated salinity. Although in comparison with fully marine areas the Baltic Sea supports fewer species, several facets of the system's diversity remain underexplored to this day, such as micro-organisms, foraminiferans, meiobenthos and parasites. In the future, climate change and its interactions with multiple anthropogenic forcings are likely to have major impacts on the Baltic biodiversity

Unintended “biological cargo” of ships entering the River Odra estuary: assemblages of organisms in ballast tanks

Water and sediment in ships’ ballast tanks provide habitats for various organisms, and thus facilitate alien species introductions. Ballast tank water and sediment of 19 ships docked in the GRYFIA Szczecin Ship Repair Yard (Szczecin, Poland) located in an area connected with the River Odra estuary (Southern Baltic), were sampled in 2009–2011 to find out if the ships could be vectors of species introductions to the estuary, already known for the presence of non-indigenous taxa. This study showed the ballast water of the ships examined to house rotifers, copepods, cladocerans, and bivalve and cirriped larvae – common constituents of zooplankton assemblages in coastal waters. The ballast tank sediment supported meiobenthic foraminiferans, nematodes, harpacticoid copepods, turbellarians, bivalves, polychaetes, and chironomid and cirriped larvae. It is not possible at this stage to judge what meiofaunal taxa constitute an alien component in the estuary biota. Macrobenthos in the ships’ ballast tank sediment examined was represented mainly by nereid polychaetes. Although the unintended “biological cargo” examined proved quite diverse and abundant, it contained few identified alien taxa. It does not seem likely than any of them could pose a threat of a biological invasion in the River Odra estuary. However, numerous species remained unidentified, and therefore assessment of the risk of alien species introduction and invasion contains a large measure of uncertainty. On the other hand, the risk as such remains, since the density of ballast water-borne organisms in all ships exceeded the allowed limits