The Emergence of Bitter Crab Disease as an International Crustacean Health Issue J.F. Morado, E.G. Dawe and R.J. Cawthorn Bitter Crab Disease (BCD) is a fatal disease of marine crustaceans caused by parasitic dinoflagellates, species of Hematodinium. Common names include Bitter Crab Syndrome (BCS) and Pink Crab Disease (PCD). The type species H. perezi was described in swimming (Liocarcinus depurator) and green crabs (Carcinus maenus) in Europe (Chatton and Poisson 1931). The parasite was first reported in North America in 1975 from blue crabs (Callinectes sapidus) in the Western Atlantic Ocean (Newman and Johnson 1975). Subsequently Meyers et al. (1987) described BCD in Tanner crabs (Chionoecetes bairdi) in the North Pacific Ocean. Since 1985 this group of parasites has globally occurred in at least 30 crustacean species, including several which are commercially important and are major players in oceanic ecosystems (Fig 1). Hematodinium-like diseases do cause significant mortalities in various crustacean populations, which impact both local economies and ecosystems. The parasites affect a broad size range of hosts, at low to high prevalences, with small decapods apparently highly susceptible to infection and mortality (see review by Stentiford and Shields 2005). Additional to mortality and abundance effects, BCD can cause bitter, aspirin-like flavor in most affected crustacean hosts. This can cause significant economic loss because the crabs are unmarketable (see Meyers et al. 1987 and Meyers et al. 1990). The cause of the adverse flavor is unknown. Surprisingly, there are many unanswered questions regarding Hematodinium- associated diseases. These include details of life cycle both within and outside the host, determination of species with the genus Hematodinium and impact of BCD on crustacean populations. A model disease system does not yet exist because of variations among the host-pathogen-environment models. There are probably several species/clades/variants in the genus Hematodinium and BCD occurs in a wide variety of oceanic environments. Perhaps Hematodinium-like infections should be considered a disease complex. Globally the geographical scale and spatial distribution of BCD/BCS/PCD is not well documented. There are several challenges associated with the many monitoring tools presently utilized, including accuracy, ease-of-use, timing and duration of monitoring programs, method of capture and overall logistics, and age (stage) determination of hosts. Ecologically, there may be ‘hot spots’ of infection and disease, determined by geography (including depth, bottom type), salinity, temperature, season and regional circulation (current) patterns. Generally, prevalence and severity of BCD/BCS/PCD peak in spring and summer. Parasites of the genus Hematodinium continue to spread geographically and to other hosts. 1 Many aspects of the life cycle of Hematodinium dinoflagellates are unknown, especially those stages which occur outside the host. Apparently dinospores are infectious to naïve crabs; whether these function as gametes is unclear (see Stickney 1978, Meyers et al. 1987). Are there alternate hosts or other parasite stages in the marine environment? Apparently amphipods may be important in transmission of the parasites (Johnson 1986, Small et al. 1986). Most susceptible crustaceans are infected during the molting cycle, with significant impact on small hosts which molt frequently. However duration of life cycles is highly variable and not well documented; shorter life cycles occur in warmer waters. Are warming oceanic temperatures increasing prevalence and severity of BCD/BCS/PCD, especially in colder regions such as southeast Alaska and Newfoundland? How will contraction of snow crab (C. opilio) habitat in the Gulf of Saint Lawrence and the Bering Sea affect distribution of the parasite? Ocean currents could regulate distribution of snow crab larvae and settlement sites, and that of the parasitic dinoflagellates. Determinants of the susceptibility of a specific crustacean host to infection with Hematodinium spp. are unknown. Molecular tools are useful for parasite identification, evaluation of pathophysiology, monitoring disease prevalence and study of parasite ecology. Apparently several species of Hematodinium exist with variable specificity and virulence. These tools can provide accurate monitoring of the parasite, identification of free-living stages of the parasite and determination of the relationship between development of disease and environmental and seasonal factors. The general pattern of Hematodinium infection and disease in crustaceans includes: parasite entry; parasite proliferation with little change in host cells or tissues; detection of parasite in host circulation with little change in host cells or tissues; continued parasite proliferation and removal of hemocytes; replacement of connective tissues, vacuolization of host epithelial tissues and infiltration (engorgement) of vascular spaces by dinoflagellate (Figs. 2, 3); reduction of host tissues; and complete cell and tissue disruption with release of dinospores. Time to death depends on host species. Hemocyte reduction leads to prolonged clotting times, i.e. infected hosts, if injured, could bleed to death. The mechanism of hemocyte removal is unknown. Overall, Hematodinium-like diseases are increasingly important to increasing numbers of marine crustacean hosts. However, there are numerous questions regarding many aspects of the host-parasite-environment relationships which require field- and laboratory-based studies. 2 References Chatton, E., and R. Poisson. 1931. Sur l’existence dans le sang des crabs. De Péridiniens parasites: Hematodinium perezi n.g., n.sp. (Syndinidae). Comptes rendus des séances de la Société de biologie et des ses filiales 105: 553-557. Meyers, T.R., T.M. Koeneman, C. Botelho, and S. Short. 1987. Bitter crab disease: a fatal dinoflagellate infection and marketing problem for Alaskan Tanner crabs, Chionoecetes bairdi. Diseases of Aquatic Organisms 3:195-216. Meyers, T.R., C. Botelho, T.M. Koeneman, S. Short, and K. Imamura. 1990. Distribution of biter crab dinoflagellate syndrome in southeast Alaska Tanner crabs, Chionoecetes bairdi. Diseases of Aquatic organisms 9:195-216. Newman, M.W., and C.A. Johnson. 1975. A disease of blue crabs (Callinectes sapidus) caused by the parasitic dinoflagellate, Hematodinium sp. Journal of Parasitology 63:554-557. Small, H.J., J.D. Shields, D.M. Neil, A.C. Taylor, and G.H. Coombs. 2006. Differences in enzyme activities between two species of Hematodinium, parasitic dinoflagellates of crustaceans. Journal of Invertebrate Pathology 94:175-183. Johnson, P.T. 1986. Parasites of benthic amphipods: dinoflagellates (Duboscquodinida: Syndinidae). Fisheries Bulletin 84:605-614. Stentiford, G.D., and J.D. Shields. 2005. A review of the parasitic dinoflagellates Hematodinium and Hematodinium-like infections in marine crustaceans. Diseases of Aquatic Organisms 66:47-70. Stickney, A.P. 1978. A previously unreported peridinian parasite in the eggs of the northern shrimp, Pandalus borealis. Journal of Invertebrate Pathology 32:212-215. Figure Legends Figure 1. World-wide reports of Hematodinium spp. and Hematodinium-like pathogens, current to 2007. Figure 2. Hematodinium in the gills of an infected Tanner crab. Figure 3. Hematodinium in the eyestalk of an infected Tanner crab. 3 4 5 .