Patterns in the natural transmission of the parasitic dinoflagellate Hematodinium perezi in American blue crabs, Callinectes sapidus from a highly endemic area

Abstract

The dinoflagellate Hematodinium perezi is a highly pathogenic endoparasite that infects blue crabs Callinectes sapidus and other decapods. Annual outbreaks of the parasite along the eastern seaboard of the USA indicate that transmission occurs at high rates; however, the timing and incidence of new infections are unknown. The aim of this study was to investigate the patterns and factors associated with the natural transmission of Hematodinium in juvenile crabs from a highly endemic site. A novel field experiment, using naive crabs as sentinels, was implemented to measure transmission. Over 965 juvenile crabs (instars C3–C10) collected from a non-endemic site were deployed for set periods of 3, 7, 10, and 14 days at a highly endemic site. Prevalence was 5.1% after a 3-day deployment and 88% after a 10-day deployment. This corresponded to a daily incidence of new infections of 1.7 and 8.8%, in the population, respectively. New infections progressed very quickly; 50% of infected crabs developed heavy infections after only 14 days. The influence of host molting on the transmission of the parasite was investigated by tagging 467 crabs using cyanoacrylate glue and small plastic tags. After 7-, 10-, and 14-day deployments, sentinel crabs were assessed and infections were found not to be associated with host molting. Lastly, two storm events, with high rainfall, strong winds, and lower temperatures, disrupted the natural transmission of H. perezi to sentinel crabs, essentially halting transmission in the coastal system. These sentinel studies indicate that transmission can occur rapidly and at very high levels in endemic sites and that it can be quickly modulated by changes in environmental conditions following storm events. Infections by Hematodinium may increase host mortality and thus may be a threat to blue crab populations in endemic areas.