Epidemiology and dynamics of shell disease in the edible crab Cancer pagurus:a preliminary study of Langland Bay, Swansea, UK

Abstract

The prevalence and severity of shell disease in the edible crab Cancer pagurus (L.) was investigated in animals collected from Langland Bay, Gower, South Wales, UK, at monthly intervals from 1997 to 1998. Shell disease is the progressive degradation of exoskeletal chitin accompanied by melanisation of the affected region. Over 50% of the crabs sampled had 1 or more black-spot lesions. The proportion of exoskeleton affected increased with the size of the crab. Male crabs showed significantly higher levels of the disease than females, a higher prevalence of black-spot lesions (63% in males, 40% in females) and a higher mean percentage of body covered by lesions (1 % in males, 0.2% in females). This difference between the sexes corresponded to an increase in ventral surface and chela infection in males. For both sexes, the dorsal carapace was the area most affected by the disease. Dorsal carapace regional breakdown revealed the areas most commonly affected were located to the posterior of the crab. Lesion location patterns suggested that sand abrasion injuries during back-burrowing behaviour of C. pagurus lead to the formation of shell disease lesions. Seasonal trends in shell disease were seen to be dependent on the onshore migration patterns of the different size classes and sexes over the sampling period.

Shell disease syndrome in the edible crab, Cancer pagurus – isolation, characterization and pathogenicity of chitinolytic bacteria

“…1a). Such lesions have previously been shown to occur on all regions of the exoskeleton (Vogan et al, 1999). SEM examination of these lesions revealed the extensive nature of the cuticular erosion into the chitinous procuticle ( Fig.…”

“…Smolowitz et al, 1992) or (ii) as a result of septicaemic infections by pathogenic bacteria originating by entry through the lesion sites (Baross & Tester, 1978 ;Vogan et al, 2001). Previous studies have found high prevalences of shell disease in the commercially fished edible crab, Cancer pagurus, from the Swansea Bay region of South Wales (Vogan et al, 1999). The current study investigates the pathogenic effects of a number of exoskeletal chitinolytic isolates both in terms of their abilities to degrade cuticular chitin (i.e.…”

“…The disease commences with the removal of the nonchitin-containing outer layer of the exoskeleton, called the epicuticle, and may occur by proteolytic and lipolytic microbial activities (Cipriani et al, 1980), predatory or cannibalistic attacks (Dyrynda, 1998), chemical attack (Schlotfeldt, 1972) or the abrasive action of sediment and\or articulated body parts (Young, 1991 ;Vogan et al, 1999). Once the underlying chitin-containing procuticle is exposed, shell degradation is largely attributed to the chitinolytic members of the lesion microbial community (for reviews see Getchell, 1989 ;Stewart, 1993).…”

Disease, parasite, and commensal prevalences for blue crab Callinectes sapidus at shedding facilities in Louisiana, USA

“…Also, high incidence of shell disease can be important in shedding systems because the causative pathogens are contagious (Sandifer & Eldridge 1974, Sindermann 1989. Fortunately for shedding facilities, if a crab successfully molts, it will shed any shell disease and will have a clean, soft shell that is appetizing and marketable (Vogan et al 1999). …”

Unchanged prevalence of shell disease in the edible crab Cancer pagurus four years after decommissioning of a sewage outfall at Langland Bay, UK

“…Ultimately the crab may die either from septicaemia (if the damaged cuticle is breached and these or other bacteria gain entry to the open haemocoele: Vogan et al 2001) or from an inability of such individuals to withdraw from the shell at ecdysis (Fisher et al 1978). Vogan et al (1999) showed an unusually high prevalence (ca. 55%) of shell disease in Cancer pagurus populations in Langland Bay near Swansea sampled in 1997-98.…”