DAO 38:143-150 (1999)  -  doi:10.3354/dao038143

Molt related mortalities of the Dungeness crab Cancer magister caused by a marine facultative ciliate Mesanophrys pugettensis

J. Frank Morado1,*, Ray H. Giesecke2, Stephen E. Syrjala1

1National Oceanic & Atmospheric Administration, National Marine Fisheries Service, Alaska Fisheries Science Center, Resource Assessment & Conservation Engineering Division, 7600 Sand Point Way NE, Seattle, Washington 98115-0070, USA
2353 Cove Road, Bellingham, Washington 98226, USA

ABSTRACT: In May of 1990, a number of Dungeness crabs Cancer magister were found dead or dying on a private beach in Samish Bay, Washington, USA. The hemolymph of a small number of randomly collected crabs was examined by bright field microscopy and found to be infected by a recently described ciliate Mesanophrys pugettensis. The same ciliate was found in subsequent 1990 collections of Dungeness, rock C. productus and kelp Pugettia producta crabs collected at the private beach and Clayton Beach, Samish Bay, Washington. M. pugettensis was again encountered in Dungeness and rock crabs collected from the same survey sites in 1991 and 1992, but not in limited beach collections in 1993. During the 1990-1992 survey period, a total of 654 Dungeness crabs were collected from the 2 study sites. Logistic regression analysis indicated that shell condition and size (i.e. carapace width) are significant predictors of ciliate infection (p < 0.0001, p < 0.005, respectively); the probability of infection is highly correlated with increase in carapace width. This is the first report implicating a ciliate as a cause of remarkable, wild crab mortalities and the first to clearly associate non-apostome ciliate infections with molting. The similarities of Dungeness crab ciliate disease to other protistan diseases of wild crustaceans is discussed, suggesting that a number of other protistan pathogens likely enter their host during or shortly after molting.

KEY WORDS: Dungeness crab · Cancer magister · Crustacean · Molt · Mesanophrys

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