Award: OCE-1652320

Overview: Disease outbreaks in the ocean are increasing, causing losses of ecologically important marine species, but the factors contributing to these outbreaks are not well understood. This project examined the relationships among genetic diversity, disease prevalence and intensity, and restoration success in two marine foundation species the seagrass Zostera marina and the Eastern oyster Crassostrea virginica. The project paired large-scale, experimental restorations and smaller-scale experiments to document both patterns and mechanisms. The experiments were co-designed with restoration practitioners and resource managers and guided by the knowledge and input of other key stakeholder groups (e.g. oyster growers, environmental organizations) in an iterative process. Graduate and undergraduate students were involved in all phases of the project, from experimental design to sample processing with state-of-the-art molecular techniques to surveys and workshops with project partners to the development of educational games to share our results. Intellectual Merit: The relationship between host genetic diversity and disease dynamics is complex. In some cases, known as a dilution effect, diversity reduces disease transmission and risk. However, the opposite relationship, known as the amplification effect, can also occur when diversity increases the risk of infection. This project provided some of the first tests of these diversity-disease relationships in marine organisms. In seagrasses, a controlled experiment revealed evidence for a dilution effect, with reduced disease intensity with greater plant genetic diversity. This benefit only occurred at elevated temperatures, suggesting the benefits of diversity may increase with climate change. A cross-ocean survey confirmed the importance of both temperature and seagrass traits for disease prevalence. In addition, a negative relationship between seagrass genetic diversity and disease prevalence in the Atlantic Ocean provided additional evidence for a dilution effect. In contrast, a large-scale experimental seagrass restoration generated some evidence for amplification: areas restored with plants from multiple source sites had greater cover, and they also had slightly higher disease prevalence. Overall, this work confirmed the key role of seagrass genetic diversity for both plant productivity and disease dynamics. With oysters, three experimental oyster reef restoration projects created for this project have expanded understanding of linkages among oyster genetic identity and diversity, parasite community prevalence and intensity, and restoration success. For example, genetic identity of the oysters used to seed experimental reefs was a strong and consistent determinant of parasite community structure on those reefs for four years post restoration. Oyster survival through time also varied by genetic identity, likely due to variation in disease and predator susceptibility, demonstrating the importance of evolutionary processes such as selection on ecological time scales. These projects highlight the importance of source selection for oyster restoration success, and suggest that using a diverse suite of sources may increase the chances of success. Broader Impacts: Working with partners to co-develop experimental restorations in two marine foundation species, as well as in additional complementary species during the project period, promoted information exchange and relationship building among scientists, practitioners, and managers, helping to identify, to characterize, and to close the science-practice gap in coastal habitat restoration. Further, these relationships informed a synthesis paper of best practices for climate adaptive restoration efforts across systems. The project also used a tiered-mentoring program to train undergraduate, Masters, PhD students, and postdoctoral researchers in field experimentation, molecular analyses, and social science approaches. Research findings were also incorporated into undergraduate courses in Conservation Biology and Foundations in Ecology and Evolution. Last Modified: 04/04/2024 Submitted by: RandallHughes