2013) and Estonia ( Kotta & Ojaveer 2012). In the last decade the sudden appearance of R. harrisii has been observed in many coastal sites of the Baltic Sea, for example, the Curonian Lagoon ( Selleckchem PF-2341066 Bacevičius & Gasiūnaitė 2008), the Odra River estuary ( Czerniejewski & Rybczyk 2008, Czerniejewski 2009), the north-eastern Gulf of Riga ( Kotta & Ojaveer 2012) and Finnish coastal waters ( Fowler et al. 2013). In the Gulf of Gdańsk it was first noted in the 1960s, but since the early 2000s a reproducing population with abundances exceeding 19 indiv./100 m2 has become established there ( Hegele-Drywa & Normant 2014).

Successful colonisation of new regions by R. harrisii was possibly due to this species’ broad tolerance to abiotic factors, especially temperature and salinity, a broad omnivorous

diet, a high rate of reproduction, and the presence of a pelagic larval stage that allows for long-distance transport in ballast waters ( Turoboyski 1973, Gollasch & Leppäkoski 1999, Normant & Gibowicz 2008, Forward 2009, Hegele-Drywa GDC-0941 research buy & Normant 2009). Apart from one paper on its distribution and abundance (Hegele-Drywa & Normant 2014), no data has been published concerning the population structure of R. harrisii in the Gulf of Gdańsk. This information could be useful for the assessment and management of non-indigenous species according to the European Commission Marine Strategy Framework Directive ( Ojaveer et al. 2014). It should also be emphasised that many

species colonise environments that are different from their native regions, which can result in the adaptation of a species’ physiology or morphology, e.g. against predators, parasites, disease agents or competitors ( Cox 2004, Paavola et al. 2005). Moreover, such adaptations have been recorded in populations separated by geographical barriers; they are exhibited by European populations of R. harrisii, which show patchy distribution patterns and genetic heterogeneity ( Projecto-Garcia et al. 2010). In crustaceans, adaptations frequently encompass changes in morphology, e.g. in the size and shape of the carapace or chelipeds or in individual mafosfamide condition ( Seed & Hughes 1995, Silva et al. 2010, Zimmermann et al. 2011, Hepp et al. 2012). Therefore, morphometric analyses are important for identification purposes, for assessing population health, fecundity and invasion potential, and for comparing crustacean populations ( Gorce et al. 2006, Duarte et al. 2008, Sangun et al. 2009). The present study describes the population structure and individual condition of the introduced population of R. harrisii in the Gulf of Gdańsk, Poland, based on animals collected between 2006 and 2010.