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The present paper reports the occurrence of the Chinese mitten crab Eriocheir sinensis H.M ilne Edwards, 1854 in the coastal waters of the Gulf of Gdańsk, and attempts an initial characterization of the crabs occurring in this area.
A newcomer to the Baltic Sea, the Chinese mitten crab is especially abundant in the Szczecin Lagoon (NW Poland), where it was first reported in 1927. Body weight, and carapace width and length, were studied in 647 individuals collected with fyke nets in the Szczecin Lagoon from 30 March – 18 April2001 and from 5–21 November 2001. 51.01% of the 543 autumn specimens were males, but only 30.97% of the 113 spring specimens were males. Body weight varied from 45.1 to 306.5 g, carapace length from 41.07 to 81.02 mm and carapace width from 46.68 to 88.85 mm. The autumn crabs were significantly heavier than the spring specimens.
Selected biological and morphometric characters of two populations of the nonindigenous Chinese mitten crab,one from the Szczecin Lagoon (SL) and the other from San Francisco Bay (SFB),b oth sampled in autumn, were analysed. The SL crabs showed a significantly higher individual weight,l ength and carapace width. Males accounted for 55% (87 individuals) of the 179 SL crabs,an d 62.9% (90 individuals) of the SFB crabs. Statistical analysis of metric characters,expr essed as a percentage of carapace width (X2),en abled four diagnostic characters to be identified: abdomen width (X11),carapace height (X3),left claw length (X7) and carapace length (X1). These jointly explain 71.75% of the differences between the SL and SFB crabs and are indicative of the distinctness of the populations.
Eriocheir sinensis H. Milne-Edwards, 1853 is a non-native species found in European waters. Analyses of mitten crabs caught in brackish waters (Gulf of Gdańsk, Poland) and in freshwater (Havel River, Germany) have indicated that numerous epibionts (possibly temporary) inhabit the dense setal mats that cover the chelipeds. Of the 950 associates found on 22 crabs collected from brackish water, the most abundant were Nematoda (82.3%), followed by Bivalvia (10.3%), Crustacea (5.6%), Oligochaeta (1.2%) and Gastropoda (0.6%). In comparison, 1280 specimens (Chironomidae – 67.6% and Halacaridae – 32.4%), were identified from 13 crabs collected in freshwater. As this crab can migrate long distances, it is capable of transporting native and non-native species via its mittened claws to new habitats.
The Chinese mitten crab Eriocheir sinensis Milne-Edwards, 1854 is a newcomer to the Baltic Sea. Previous studies have shown that since the 1940s single large specimens of this species have been caught annually in Polish waters. The invasion of the Chinese mitten crab has been reported from many European countries, including Poland, where it is especially abundant in the Odra Estuary. Of 186 specimens captured in Lake Dąbie in August 1998, 45% were females and 55% males. The carapace width of these crabs varied between 53 and 88 mm and the average wet weight was 169±45.3 g.
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