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Diseases of Aquatic Organisms

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DAO 68:83-87 (2005)  -  doi:10.3354/dao068083

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

Adam Powell, Andrew F. Rowley*

Department of Biological Sciences & Institute of Environmental Sustainability, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK
*Corresponding author. Email:

ABSTRACT: Shell disease is a bacteria-associated degradative disease of the crustacean exoskeleton that leads to formation of extensive lesions in the cuticle with ultimate involvement of haemocoelic septicaemia. Field surveys of edible crabs Cancer pagurus from Langland Bay, Gower, UK, from February 1997 to March 1998 had revealed unusually high prevalence (ca. 55%) of this disease amongst the population, and it was suggested that one of the predisposing factors might have been the presence of raw sewage in this area. Since February 1999, a local raw sewage outfall affecting this area has been decommissioned, raising the possibility that the prevalence and severity of this disease could have become reduced as a result of the cessation of sewage exposure. Therefore, the aim of this study was to compare the prevalence and severity of shell disease in edible crabs from Langland Bay pre- and post-sewage discharge. The overall prevalence of shell disease from February 2003 to March 2004 was 59.2%, and in only 1 size class (80–99 mm carapace width, males) was the prevalence higher in 2003–04 than in 1997–98. In terms of severity, only smaller crabs (60–199 mm width) showed a significant reduction in 2003–04 compared with 1997–98. No changes were found in the severity of the disease in different regions of the exoskeleton of infected crabs between the 1997–98 survey and the present work. Overall, it is concluded that no significant changes in the occurrence of shell disease have resulted from the improvement in water quality (in terms of faecal pollution) at this site, suggesting that sewage pollution is probably not a major contributory factor to this disease.

KEY WORDS: Shell disease · Cancer pagurus · Crustacea · Pollution

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