2 . 2 Shell Disease in Red Crabs 



Shell disease in red crabs from three continental shelf 

 canyons (Table 3) was studied by Young (1988, in press) (Fig. 5), 

 who proposed a rating scale of 1-5 to estimate the severity of 

 the disease. A rating of "1" was given to crabs without visible 

 evidence of shell disease, "2" to those with up to 10 black 

 spots; "3" to those with >10 black spots or <10% of the body 

 showing shell blackening; "4" to those with large areas affected 

 by blackening of 10-50% of the body, and "5" crabs with 

 blackening of >50% of the body, and/or open lesions present, or 

 with one or more missing appendages. Crabs with missing 

 appendages were often blackened at the site of the break(s). 

 Ratings of moderate to severe ("4" or "5") were assigned to 13% 

 (27/202) of the specimens from the Hudson Canyon, 30% (23/77) 

 from Block Canyon, and 19% (21/110) from Atlantic Canyon. The 

 prevalance of shell disease in crabs from the canyons appears to 

 be significant, especially since video films of the sea bottom 

 showed soft to silty sediments and the absence of rocks or crags 

 associated with physical causes of shell damage (National 

 Underwater Research Program, Univ. of Conn.). R. R. Young 

 (unpublished data) also found shell disease in a small collection 

 of red crabs from the Middle Atlantic Bight deposited in the 

 Smithsonian Institution, Washington, DC, over a century ago 

 (1884). Preliminary microbiological studies (Bullis, et al., 

 1988) on eroded shell lesions in red crabs identified several 

 species of bacteria ( Vibrio spp. and Flavobacter spp.) as well as 

 several fungi that deserve further investigation. 



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