comm.). Individuals have also been recorded during diving surveys at 1 m depth (Anna Dziubińska, pers. comm.), as well as during dredging from a research vessel at greater depths. There have been similar situations in other parts of the world, where this species lives mostly in shallow estuaries and lagoons ( Diamond et al. 1989, Gonçalves 1995, Roche et al. 2009). Our analyses also confirmed the patchy distribution of R. harrisii in the Gulf of Gdańsk, which may be the result of larval retention mechanisms ( Cronin, 1982 and Cronin and Forward, 1986, Projecto-Gracia

et al. 2010). The population’s low mobility and its variable occurrence have also been recorded in the Iberian Peninsula: R. harrisii was found only in the Mondego Estuary (central Portugal) and in the River Guadalquivir on the Atlantic south Z-VAD-FMK ic50 coast of Spain ( Gonçalves et al. 1995). However, not only larval retention mechanisms affect

the occurrence and distribution of this species. Food availability, bottom structure and physico-chemical conditions determine the occurrence range of non-native species ( Colautti and MacIsaac, 2004 and Galil et al., BYL719 molecular weight 2009). This is the case in the Gulf of Gdańsk, where the sampling points differ with regards to bottom composition, and various benthic community compositions, which can also determine the probable occurrence and density of R. harrisii. Unfortunately,

there are very scanty data in the extant literature on the abundance of R. harrisii, which makes comparison of our data difficult. The only available information relates to the shallow brackish-water limans (coastal lagoons) of the Sea of Azov ( Zaitsev & Öztürk 2001). Compared to these habitats, the density of the mud crab estimated in Puck Bay was significantly lower. It also has to be pointed out that the application of different sampling methods makes comparison hard. In the majority of studies baited traps Atezolizumab mw were used (e.g. Rychter, 1999 and Roche and Torchin, 2007, Czerniejewski et al. 2009, Roche et al. 2009). The large variety of benthic species occurring in Puck Bay that constitute established food items of the Harris mud crab’s diet, especially gammarids (Czerniejewski & Rybczyk 2009, Hegele-Drywa & Normant 2009), may partly explain the highest density recorded in this region. The lowest density of mud crabs was reported near Gdynia and Sopot, on a bottom covered by mussels and barnacles, where gammarids are frequent. This is somewhat surprising, because both mussels and barnacles can offer the mud crab perfect concealment and, together with the gammarids, suitable food resources (Czerniejewski & Rybczyk 2009, Hegele-Drywa & Normant 2009). R. harrisii was not recorded only in the vicinity of Gdańsk, where the most common organisms were C. crangon and C. glaucum.