Preliminary results on the seasonality and life cycle of the parasitic dinoflagellate causing bitter crab disease in Alaskan tanner crabs (Chionoecetes bairdi).

Tanner crabs (Chionoecetes bairdi) from the Sullivan Island area of southeast Alaska were sampled for 1 year to determine the prevalence and intensity of the parasitic dinoflagellate which causes bitter crab disease (BCD). The prevalence and intensity of infection were the greatest in the summer, declined in the fall and winter, and increased again in the spring. A possible relationship between softer, newer shells and higher levels of parasitism was also observed. In vivo transmission studies in the laboratory suggested there are several morphologically different forms of the vegetative cell of the BCD dinoflagellate which occur prior to sporulation of the parasite. In addition, it appears that both the two spore types produced by the parasite are infectious by injection and that there is no ploidy difference between the two spore types and the vegetative cell, suggesting that the two spore types may not represent separate sexes.