Native oyster species were historically dominant ecosystem engineers that provided critical ecosystem services such as biofiltration and economic value through fisheries. Their populations were decimated over the last century through overfishing and habitat degradation, often to less than 1% of historical abundance. Extensive efforts are underway worldwide to restore populations of native oyster species, including in the Chesapeake Bay, but these have largely been ineffectual, partly due to the lack of understanding of oyster-reef-sediment dynamics in complex nonlinear systems. A realistic mathematical model that can account for the dynamics at various spatial scales will enable us to study the underlying processes of these systems. With an understanding of nonlinear dynamics, such as multiple stable states due to feedbacks between oysters and the physical environment, and the effects of different spatial scales on population viability, effective restoration strategies can be devised. In this project, oyster-reef-sediment dynamics will be modeled at three scales: local, whole reef, and metapopulation. Local models will address reef geometry and how it affects feedback interactions. At the reef scale, a reaction-diffusion-advection model for oysters and sediment will be used to explain the spatial pattern of the reef and determine optimal reef geometries for restoration. Metapopulation models, including ones with connectivity between reefs based on realistic hydrodynamic modeling under various dynamic conditions, will be used to locate potential restoration sites and to estimate the risk of extinction due to environmental perturbations. This project will lead to advances in several branches of mathematics, including spatiotemporal pattern formation, metapopulation model analysis and simulation, and stochastic coupled systems.
Results of the project will guide ongoing eastern oyster restoration efforts by federal, state and nonprofit agencies in the Chesapeake Bay and other locations along the Atlantic and Gulf of Mexico coasts, as well as for other native oyster species globally. In doing so, the project will contribute significantly to achievement of Executive Order 13508, signed in 2009, which has the goal of restoring oyster populations in 20 tributaries of Chesapeake Bay by 2025. The project is complementary to and will be integrated with an active field research program to parameterize the models and ultimately inform the relevant agencies on optimal restoration strategies. The project will also lead to training of undergraduate and graduate students in mathematical biology. This type of training is timely due to the scarcity of scientists capable of modeling in marine conservation biology and fisheries stock assessment.
