Biotic and abiotic drivers of pathogen transmission in marine system under the influence of climate change

The emergence of pathogens in marine systems affects us all by damaging fisheries and their supporting ecological communities. Indeed, two regional icons, blue crabs and oysters, have seen major declines due to disease. The goal of this study is to understand how climate change and other human impacts alter disease transmission in marine systems.

The transmission of a pathogen, Hematodinium perezi, to the American blue crab, Callinectes sapidus will be examined in relation to filter feeding, cannibalism, fishing pressure, and climate change. Filter feeding is widespread in marine systems and may act to reduce transmission of pathogens. Cannibalism may reduce susceptible juvenile crabs and, thus, lower transmission.

Because fishing pressure removes adults, countering cannibalism, commercial fishing may enhance susceptible juveniles and increase transmission in crab populations. These biotic factors are common to many marine systems; yet, they have received little attention in terms of their effects on disease transmission. Climate change magnifies these dynamics through direct and indirect effects on both the host and pathogen dynamics.

This project builds on its research activities by engaging teachers and students in important concepts in marine biology, disease ecology, and climate change. Science teachers will engage in internships, workshops, and field courses to leverage the project’s research findings for delivery in the classroom. The educational component will build the capabilities of teachers, graduate students, undergraduate summer interns, and undergraduates at William & Mary and VIMS through training in advanced techniques in several disciplines.

An online model will simulate the effects of disease on marine systems, making the research findings even more accessible to scientists, educators, and students. Outreach programs at each institution will further inform thousands of people about the project’s research. Collectively, these activities will enhance the visibility of this research to the broader scientific community, educational community, and general public.

Disease processes can be very different between marine and terrestrial ecosystems. In marine systems, biotic factors such as top-down control of phytoplankton through filter feeding, density-dependent cannibalism in predator populations, and industrialized fishing operate on grand scales that alter the dynamics of host populations; however, their influence on disease ecology has received little attention.

An investigation into the blue crab – Hematodinium perezi system allows insights into the interactions among these factors. Hematodinium perezi is a pathogen of blue crabs that is hyper-endemic in the coastal bays of the eastern USA. The pathogen has a predilection for juvenile crabs.

Cannibalism removes large numbers of juveniles, potentially suppressing outbreaks. In contrast, fishing pressure removes large numbers of adults, potentially enhancing the susceptible juvenile population. In addition, filter feeding by oysters may reduce transmission of H. perezi, and when combined with high abundance such as in oyster reefs, may negatively influence disease transmission to blue crabs.

Overlying these factors is the ecosystem-level disruption caused by climate change, which includes additional enhancements to pathogen transmission through increased proliferation and dispersal. These factors can be modeled to provide insight into their influence over host – pathogen dynamics. This study has five objectives: (I) integrate disease and seasonality into a population model of the blue crab; (II) examine the interactions between filter feeders in the ecosystem and pathogen transmission; (III) explore how natural mortality (predation, cannibalism) and fishing pressure affect transmission and incidence of the pathogen; (IV) examine the influence of climate change on disease transmission and dispersal; and (V) analyze nonlinear mechanisms for broader application to wildlife disease dynamics.

Although this study focuses on the transmission dynamics in the blue crab – Hematodinium perezi system, it is applicable to other marine systems impacted by similar stressors.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.