Ecological Determinants of Hematodinium Epidemics in the American Blue Crab

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0723587Fishing pressure and habitat degradation are severe and pervasive threats to coastal marine ecosystems. Both are known to impact the dynamics of host movement, aggregation, nutrition, and mortality, and therefore the transmission of disease. The role of fishing pressure in facilitating the emergence and spread of diseases in marine systems is poorly understood, although circumstantial evidence suggests that overexploitation has contributed to the emergence of disease in several marine fisheries. In this research, scientists from Virginia Institute of Marine Sciences and from Old Dominion University will investigate how fishing pressure and declining water quality combine with the hydrography of small coastal estuaries on the Delmarva peninsula to promote outbreaks of a pathogenic parasite, Hematodinium, in blue crabs. Overlying seasonal outbreaks of the disease is an intensive fishery for the blue crab, which alters the population structure of the host by removing the more disease-resistant adults. Thus, the fishery increases the relative number of susceptible individuals both directly, by removing adults, and indirectly by releasing juveniles from density-dependent cannibalism. Potentially counter-balancing these anthropogenically-induced effects are the rapid growth rate of the blue crab, a seasonal nadir in infection dynamics, and an ontogenetic shift in host susceptibility to infection that may constrain transmission of the disease. Over five years of work, the research will; assess the prevalence and spatial distribution of Hematodinium infections in juvenile and adult blue crabs in relation to the topology of coastal bays on the Delmarva Peninsula; determine the effect of the blue crab fishery on the population structure of healthy and diseased blue crabs; determine how environmental factors affect infections in blue crabs and how they affect the life history and spread of the pathogen; clarify the modes of transmission in the life history of the parasite and their efficiencies in relation to host factors; model the underlying mechanisms that control the spread of disease and predict outbreaks in relation to changes in fishing pressure and environmental stressors.In terms of broader impacts, the disease causes significant annual losses to national and international crustacean fisheries. This study will produce an epidemiological model capable of integrating local environmental change and fishing pressure with disease dynamics with broad application to several finfish and shellfish populations. The PIs will continue their strong involvement with mentoring of undergraduates, graduate students, and postdoctoral fellows in this project, including participation in NSF REU programs at VIMS and ODU. Three outreach programs will include an annual meeting with fishermen, resource managers and environmental stewards, an outreach program in local high schools, and development of a website on Hematodinium.