also noted (Sawyer, 1982), i.e., "Specimens with gills judged to 

 be 100% black often had external blackening and shell erosion. 

 Black gills were often melanized extensively with necrosis of 

 gill cuticle or entire gill filaments." 



Mortalities attributed to effects of shell disease have been 

 observed and reported, occasionally at high levels, in impounded 

 populations of crustaceans. In lobsters, death has been 

 associated with progressive erosion and destruction of gill 

 membranes, with resultant reduced oxygen uptake, especially in 

 hypoxic situations. Estrella (personal communication) observed 

 one episode of natural mortality from undetermined causes among 

 small lobsters at Racing Beach, Falmouth, Massachusetts in 1983, 

 where the numbers of dead lobsters went from 0% in May and June 

 to 3.78% in July, 2.3% in August, and then declined to <1% in the 

 autumn. In shrimp, failure to complete molting because of shell 

 adhesions has been identified as a cause of mortality. Death may 

 also result from secondary systemic infections after the 

 exoskeletal barrier has been breached, especially in the presence 

 of high populations of facultative pathogens. Additionally, it 

 is quite likely that severely affected animals would be more 

 vulnerable to predation. 



Some limited information exists about possible association 

 of shell disease, environmental degradation and mortalities of 

 crustaceans. Pearce (1971) reported field observations of high 

 mortality of crabs and lobsters in and around sewage sludge and 

 contaminated dredge material disposal areas of the New York 

 Bight, and attributed the deaths to observed "fouling and 

 necrosis of gill tissue, which decrease respiratory surface area, 

 together with the low oxygen concentrations in the bottom water 

 of the waste disposal areas." 



In addition to direct mortality, it is reasonable to expect 

 that damaged or crippled crustaceans would be more subject to 

 predation or cannibalism than healthy ones -- and there is some 

 limited information to support this. In a study of caridean 

 shrimp ( Crangon septemspinosa ) from the New York Bight, Gopalan 

 and Young (1973) observed in aquarium studies that individuals 

 with advanced shell disease were attacked and eaten by the 

 healthy cannibalistic survivors. 



Reductions in crustacean populations may be brought about by 

 many factors, including predation, disease, and overfishing. 

 Some of the best estimates of mortality have been obtained by 

 studying the feeding habits and gut contents of predatory 

 species. For example, juvenile and adult rock crabs are known to 

 make up a large portion of the diet of predatory fish such as 

 cod, skate, smooth dogfish, and striped bass, while juveniles are 

 known to be fed upon extensively by lobsters (Bigford, 1979). 

 Reilly (1975) estimated that 75-85% of second-year class rock 

 crabs, and 68-80% of the third-year class are consumed by 

 predators in coastal waters. There are no comparable estimates 

 for similar losses in offshore or continental shelf habitats. 



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