Dynamics of shell disease in the edible crab Cancer pagurus: a comparative study between two sites on the Gower Peninsula, South Wales, UK

Abstract

Shell disease syndrome is a degradative condition of the crustacean exoskeleton which results in the formation of black-spot lesions. Field surveys on the edible crab Cancer pagurus (L.) population at 2 sites in the Gower Peninsula of South Wales, UK, namely Langland Bay and Rhossili causeway, revealed similarities in the prevalence of shell disease but differences in the severity. Male crabs from Langland Bay displayed significantly greater severities of the disease on the dorsal carapace and ventral surfaces than those in Rhossili. The greatest severities of the disease in Langland were attributable to sand abrasion injuries during back-burrowing behaviour and prolonged exposure to high numbers of chitinolytic bacteria. Lower severities of shell disease in males from Rhossili were a reflection of the inability to back-burrow due to the nature of the onshore sediment, and hence the crabs were only exposed to low levels of chitinolytic bacteria in the water column. On areas of the causeway that permitted back-burrowing, the chitinase enzyme activities in sediments were significantly lower than those in Langland Bay. It is concluded that the potential for crustacean shell degradation is higher at Langland than Rhossili, but whether the differences in chitinolytic abilities of the sediments at the 2 sites are a result of differences in pollution levels or simply of different substratum types, remains to be determined.

Effect of the copepod parasite Nicothoë astaci on haemolymph chemistry of the European lobster Homarus gammarus

“…However, since ammonia is excreted from gills (Taylor & Taylor 1992), significant damage to this tissue may be expected to result in ammonium and other cellular metabolites becoming accumulated and therefore elevated in the haemolymph. Thus either the gill damage caused by N. astaci was not sufficient to impair ammonia excretion, or there is a switch in nitrogenous wastes to products such as urate or urea (Dykens 1991, Chen et al 1994, Vogan & Rowley 2002 which were not examined. Another explanation may be that since ammonia is a minor component of haemolymph, and as all lobsters examined were parasitized by N. astaci to some extent, any increase in levels was not able to be resolved as easily as other constituents assayed for.…”

Shell disease syndromes of decapod crustaceans

“…The studies of shell disease in edible crabs ( C . pagurus ) in Langland Bay (Gower, UK) by Vogan and colleagues (Vogan et al, 1999 , 2001 , 2002 ; Vogan & Rowley, 2002 ) were from intertidal zones affected by the input of raw sewage waste. While it was not thought that the coliforms in such sewage were directly contributing to shell disease, the accompanying large amount of organic matter could stimulate more microbial growth in sediments.…”