Compositional characteristics of green crab (Carcinus maenas)
Introduction
The European green crab, Carcinus maenas, has proven to be a very successful invader outside of its natural habitat in the coasts of Eastern Europe (Jamieson, Grosholz, Armstrong, & Elner, 1998), invading South Africa (Le Roux, Branch, & Joska, 1990), Australia (Jamieson et al., 1998), and both the west (Cohen, Carlton, & Fountain, 1995) and east (Glude, 1955) coasts of North America. Attributes that contribute to their success as an invasive species include a very high reproductive output, a planktonic larval phase, tolerance of a wide range of salinity and temperature, and the ability to thrive in densities of several individuals per square meter (Crothers, 1968; Young, Komarow, Deegan, & Garritt, 1999).
Green crab was introduced to the Atlantic coast of North America during the mid-1800s in the Cape Cod area (Glude, 1955). This initial population then expanded northwards and reached Nova Scotia in the early 1950s (Elner, 1981; Glude, 1955; MacPhail, Lord, & Dickie, 1955). Expansion then continued during the next 30 years, both into the Bay of Fundy and in a north-eastern direction along the southern coast of Nova Scotia, in the latter case possibly slowed somewhat by the relatively small number of estuaries and cool summer water temperatures along that shore. It appears that, by the early 1990s, green crabs were established in the southern Gulf of St. Lawrence, where warm summer temperatures and numerous estuaries and bays could be considered optimum habitats for them. It is likely that the green crab will build up to very high numbers in the southern Gulf of St. Lawrence. An example of this can be seen in Antigonish Harbour, where green crabs have achieved densities exceeding 1 crab/1 m2 in less than 10 years after their arrival (Campbell, 2001).
Many studies have examined the ecological impact of invasive green crab populations on pre-invasion flora and fauna (Cohen et al., 1995). Green crabs are very aggressive omnivores (Le Calvez, 1987), and gut content studies have found representatives of many groups, including bivalves (Cohen et al., 1995), snails (Hadlock, 1980), annelids (Gee, Warwick, Davey, & George, 1985), crustaceans (Ropes, 1968), and even algae (Elner, 1981). In particular, though, green crabs tend to have the greatest impact on bivalves (Elner, 1981) and have been associated with collapses of softshell clam (Mya arenaria) in New England (Glude, 1955) and severe reductions of the clams Nutricola tantilla and confusa on the west coast of North America (Grosholz, Ruiz, Dean, Shirley, Maron, & Connors, 2000). Despite their relatively small size (maximum carapace width approximately 95 mm) (Grosholz et al., 2000), green crabs use their chelae very effectively to open and consume bivalves and can even open bivalves with relatively thick shells, such as quahaugs (Mercenaria mercenaria) and oysters (Crassostrea virginica). Given their penchant for shellfish, and their ability to thrive at high densities, the invasive green crabs pose a considerable threat to both wild and aquacultured shellfish in the southern Gulf of St. Lawrence. In addition to shellfish, there is a considerable potential for green crabs to act as competitors or predators for various life history stages of two species of commercially important crustaceans, the rock crab (Cancer irroratus) and the American lobster (Homarus americanus) (Gillis, MacPherson, & Rattray, 2000). Given the likelihood that green crab may become established in most of the Atlantic provinces, and the potential for considerable impact on aquaculture and crustacean resources, some regional harvest may be implemented in order to control numbers in selected areas of concern. Cost recovery of such an operation would be facilitated by developing uses for components of green crab. The present study represents the first step in exploring the economic potential of the green crab and reports on its proximate, amino acid and fatty acid compositions.
Section snippets
Materials and methods
Green crabs (C. maenas) were collected from four sites, Antigonish harbour, Pomquet harbour, Merigomish Bay, and the Little Dover-Canso region (Table 1) using cylindrical traps which were 60 cm in length, 35 cm in width, constructed of a coated 1 × 1 cm wire mesh. Traps were baited with mackerel and deployed at depths of 1.5–2 m. Soak time was 3 h, after which the traps were hauled and the crabs were placed on crushed ice until euthanized by freezing.
Meat from the body and claw portions was
Results and discussion
Antigonish, Pomquet, and Merigomish Harbours are relatively small estuaries situated in the southern Gulf of St. Lawrence. Although the freshwater input into these estuaries is modest, they still experience somewhat reduced salinities (ranging from 20 to 30 ppt depending on precipitation) and temperatures a few degrees above outer coastal areas. The sites sampled in these estuaries were characterized by soft bottoms and seagrass (Zostera marina) beds. The Little Dover-Canso sites were situated
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