Effects of the parasitic dinoflagellate Hematodinium perezi on blue crab (Callinectes sapidus) behavior and predation

Blue crabs (Callinectes sapidus) living in high salinity regions along the Atlantic and Gulf coasts of the United States are subject to infection by the parasitic dinoflagellate Hematodinium perezi with a prevalence that can exceed 50%. Infections are usually lethal, thus H. perezi infection represents a significant cause of mortality in many crab populations. Most studies of this host-parasite interaction have focused on epidemiology, host-pathogen dynamics, and pathogen transmission; little is known about the impact of the parasite on host behavior and population dynamics. We examined the effects of H. perezi on blue crab mortality from predation, activity patterns, and habitat use. Infected crabs suffered significantly higher predation than uninfected crabs when tethered in the field. Similarly, infected juvenile crabs were preyed upon significantly more often than uninfected conspecifics when exposed to a predatory adult crab in laboratory experiments. Laboratory experiments also revealed that the behavior of infected and uninfected crabs differed in ways that affected their risk of predation. Compared to infected crabs, uninfected juvenile crabs buried more frequently, moved less, and used oyster shell substrate more often when a predator was present. These differences do not appear to be driven by olfactory cues because chemosensory assays show that H. perezi infections do not affect detection of juvenile crabs by adult crabs, nor infected juvenile crab chemosensory responses to adult crabs. Our results indicate that H. perezi infection alters crab behavior in ways that enhance predatory culling of infected crabs, and this in turn may limit the spread of the parasite.