139 



Abstract.— On the eastern seaboard of 

 the United States, populations of the 

 blue crab, Callinectes aapidus, experi- 

 ence recurring outbreaks of a parasitic 

 dinoflagellate, Hematodinium perezi. 

 Epizootics fulminate in summer and 

 autumn causing mortalities in high- 

 salinity embayments and estuaries. In 

 laboratory studies, we experimentally 

 investigated host mortality due to the 

 disease, assessed differential hemato- 

 logical changes in infected crabs, and 

 examined proliferation of the parasite. 

 Mature, overwintering, nonovigerous 

 female crabs were injected with lO'^ or 

 10^ cells of//, perezi. Mortalities began 

 14 d after infection, with a median 

 time to death of 30.3 ±1.5 d (SE). Sub- 

 sequent mortality rates were greater 

 than SG'/r in infected crabs. A relative 

 risk model indicated that infected crabs 

 were seven to eight times more likely to 

 die than controls and that decreases in 

 total hemocvte densities covaried signif- 

 icantly with mortality. Hemocyte densi- 

 ties declined precipitously (mean=48'^ ) 

 within 3 d of infection and exhibited 

 differential changes in subpopulations 

 of gi-anulocytes and hyalinoc)d;es that 

 lasted throughout the course of the 

 infection. Crabs that did not present 

 infections after injection (i.e. "immune" 

 hosts) did not show hemocytopenia and 

 exhibited significant long-term (21-27 d) 

 granulocvtemia. Detection of the para- 

 site in the hemolymph of infected crabs 

 increased from approximately 30'^i after 

 14 d to 60'7< after 21 d to 100% after 

 35 d. Plasmodial stages were, however, 

 detectable in histological preparations 

 of the heart within 3 days of infection 

 and increased in number over 5 and 

 7 days. Sporulation of the parasite 

 occurred over a short time (at least 4 

 d, after 43 d of infection I and did not 

 culminate in the immediate death of 

 the host. Hematodinium perezi repre- 

 sents a significant threat to the blue 

 crab fisheries in high-salinity estuar- 

 ies. Although the parasite infects male 

 and female crabs, it may have a greater 

 impact on mature females as they move 

 to higher salinities to breed. 



Mortality and hematology of blue crabs, 

 Callinectes sapidus, experimentally infected 

 with the parasitic dinoflagellate 

 Hematodinium perezi* 



Jeffrey D. Shields 

 Christopher M. Squyars 



Department of Environmental Sciences 



Virginia Institute of Marine Science 



The College of William and Mary 



P.O. Box 1346, Gloucester Point, VA 23602 



E-mail address (for J D Shields): |eff(givims edu 



Manuscript accepted 23 August 1999. 

 Fish. Bull. 98:139-152 (2000). 



Hematodinium perezi is a parasitic 

 dinoflagellate that proliferates in 

 the hemolymph of several crab spe- 

 cies. In the blue crab, Callinectes 

 sapidus, H. perezi is highly patho- 

 genic and usually kills the host. 

 The main symptom of the infection 

 is lethargy. Heavy infections are 

 characterized by discolored (brown, 

 yellow, milky or chalky ) hemolymph 

 that does not clot. The disease oc- 

 curs in blue crabs in high-salinity 

 i>\Yi() waters from Delaware to 

 Florida, and in the Gulf of Mexico 

 (Newman and Johnson, 1975; Mes- 

 sickandSinderman, 1992). In 1975, 

 Newman and Johnson (1975) re- 

 ported a prevalence of 309r in blue 

 crabs from Florida; the effect of this 

 disease on the blue crab population 

 was thought to be high. 



In 1991 and 1992, prevalences of 

 infection up to IQO'^/r were found in 

 blue crabs (mean prevalence=43'^, 

 several locations from 709f to 100*^, 

 /7=971) from coastal bays in Mary- 

 land and Virginia (Messick, 1994). 

 Commercial watermen reported re- 

 duced catches, lethargic and mor- 

 ibund crabs in pots and shedding 

 facilities, and crabs that died soon 

 after capture (Rux, Oesterling'). In 

 1996 and 1997, IQ'A to 40% of adult 

 crabs from the eastern portions of 

 Chesapeake Bay in Virginia were 

 infected.- The disease has a low 

 prevalence or does not occur in the 



larger, riverine ("bayside") fishery; 

 it appears most detrimental to the 

 coastal ("seaside") crab fisheries. 



Outbreaks of infestation by Hema- 

 todinium spp. have caused concerns 

 to several major crustacean fisher- 

 ies. Significant population declines 

 and economic losses have been 

 reported for the Tanner iChion- 

 oecetes bairdi) and snow (C. opilio) 

 crab fisheries of Alaska and New- 

 foundland (Meyers et al.. 1987, 

 1990; Taylor and Khan, 1995),'^ the 

 Norway lobster (Nephrops norveg- 

 icus) fishery of western Scotland 

 (Field et al., 1992), and the velvet 

 crab iNecora puber) fishery of west- 

 ern France (Wilhelm and Miahle, 

 1996). The parasite causes a condi- 



Contribution 2241 from the Virginia Insti- 

 tute of Marine Science, The College of 

 William and Marv, Gloucester Point, VA 

 23602. 



Rux, S. 1993. Red Bank Seafood Co., 

 Box 37 Marionville, VA 23408. Personal 

 common. ; Oesteriing, M. 1993. VASG, 

 Virginia Inst. Marine Science, Gloucester 

 Point. VA 23062. Personal commun. 

  Shields. J. D. 1997. An investigation into 

 the epizootiology of Hematodinium perezi, 

 a parasitic dinoflagellate in the blue crab, 

 Callinectes sapidus. Saltonstall-Kennedy 

 Progi'am, National Marine Fisheries Ser- 

 vice, NOAA. Final Report. 

 Prevalences in Newfoundland are now at 

 1-15"^; in the northern bays. Taylor, D. 

 1998. DFO. CP 5567, White Hills, St. 

 Johns, Newfoundland, Canada, AlC 5X1. 

 Personal commun. 



