77), whereas males showed an isometric increase in weight with increasing CW (b = 3.02) ( Figure 5). The CW: WW ratio for all specimens was determined by the function CW = 0.0005 WW2.90 (R2 = 0.96, p < 0.05). The condition factor K of all R. harrisii taken together varied from 0.02 to 0.08 (mean 0.05 ± 0.01; n = 601). In females (n = 276) it ranged from 0.03 to 0.08 (mean 0.06 ± 0.08), whereas in males (n = 325) it was significantly lower (p < 0.05),

from 0.02 to 0.07 (mean 0.04 ± 0.06). The water content in the mud crabs varied from Tanespimycin cost 57.9 to 91.5% of the total body weight (mean 73.6 ± 7.5%; n = 248), but this differed between juveniles and adults and between the sexes (juveniles: 65.1–87.5%, mean 74.1 ± 5.5%, n = 87; females: 57.9–91.3%, mean 74.9 ± 8.7%, n = 79; males: 58.6–91.5%, mean 71.8 ± 7.9%, n = 82). The water content was not significantly related (p > 0.05) to carapace width (CW), although there were statistically significant differences (p < 0.05) in water content between both sexes and between males and juveniles. Invasive species, for many reasons such as their broad environmental tolerances, can reduce native biological diversity and even become dominant organisms in non-native regions by replacing or coexisting with indigenous species (Ba et al. 2010). Although Rhithropanopeus harrisii has been present in the Gulf of Gdańsk for at least a decade, its negative influence on native

species has been not reported 17-DMAG (Alvespimycin) HCl ( Hegele-Drywa & Normant 2014). Between 2006 and 2010, over 200 specimens of R. harrisii were collected each year, except for 2006 and 2009. In 2006, sampling started later than usual, and in 2009, Ku-0059436 ic50 in order to obtain information on seasonal variations in crab abundance, the material was collected from only two depth profiles (see Hegele-Drywa & Normant 2014). Sexually mature specimens dominated the samples, and the sex ratio

was skewed slightly towards more males: this has been observed in other populations inhabiting Polish waters (i.e. the Dead Vistula River, the Vistula Lagoon and the Odra Estuary) (Turoboyski 1973, Rychter 1999, Normant et al. 2004, Czerniejewski & Rybczyk 2008, Czerniejewski 2009), Chesapeake Bay (Ryan 1956) and the Panama Canal (Roche & Torchin 2007). The dominance of males over females occurs frequently in crab populations, including other species from the Xanthidae family (De Goes & Fransozo 2000, Warburg et al. 2012). According to Morgan et al. (1988) this is normal in natural environments, but for high spawning rates it is more advantageous when there is a higher proportion of females. Laboratory studies showed that R. harrisii spawning was greater when males were less abundant than females, perhaps because a few males can mate with many females ( de Rivera et al. 2003). Additionally, females would be less vulnerable to attack by more aggressive males while moulting (Morgan et al. 1988). In 2009–2010 juveniles (< 4.