He reported large numbers of crabs in the shallow bays of the Dead Vistula during the summer. The optimum for egg laying and embryonic development lies at temperatures above 20 °C ( Kujawa, 1957, Christiansen and Costlow, 1975, Gonçalves et al., 1995 and Forward, 2009). In an ecosystem context, it is crucial to know
where non-native species occur and how they are distributed. It can be inferred from the results of this study that R. harrisii is now a quite widely, though patchily, distributed and well-established component of the benthic communities in the Gulf of Gdańsk. On the one hand this situation could be due to larval retention mechanisms, but on the other it may be determined to a significant extent by tolerance of environmental factors and the community in which the species lives. The R. harrisii population inhabiting the
Gulf of Gdańsk has a strong reproductive click here potential, which has been demonstrated by the increasing numbers of juvenile individuals. In addition, the stable salinity lowers the metabolic costs associated with osmoregulation with respect to those in oligohaline waters ( Normant & Gibowicz 2008). Therefore, more energy is available for growth and reproduction. The depth-related thermal conditions, the stable salinity as well as the permanent availability of food in the Gulf of Gdańsk lead to the conclusion that this basin offers favourable conditions for the life and development of R. harrisii. Although at present R. harrisii does not pose a threat to the local aquatic community, its rate of spreading and population dynamics patterns have to be monitored. It should be kept in mind that despite its small size,
R. harrisii TSA HDAC is a non-native, omnivorous organism, with a high reproductive potential. Therefore, its possible effects on the aquatic habitat and community of the Gulf of Gdańsk have to be assessed; this is the aim of further research on R. harrisii inhabiting the Gulf of Gdańsk (Hegele-Drywa et al. in prep.). We would like to thank Barbara Szwarc, Anna Radoń and Agnieszka Kąkol for their cooperation in collecting the material for this study and their contributions to this research. The help of Halina Kendzierska from the home department in producing the maps is also acknowledged. “
“The introduction of alien Sclareol species intensified during the second half of the 20th century. As a consequence, biological invasions on a global scale are currently one of the greatest threats to terrestrial and aquatic ecosystems. These phenomena are dynamic in both time and space (Drake 2009). Introductions of allochthonous species into the Baltic Sea have been observed for many years (Krylov et al., 1999, Laine et al., 2006, Orlova et al., 2006, Rodionova and Panov, 2006, Antsulevich, 2007, Bielecka and Mudrak, 2010, Jaspers et al., 2011 and Zaiko et al., 2011). Within the zooplankton, three new invasive species of Cladocera and one ctenophoran have been recorded in the last 25 years (Bielecka et al.