From plants to populations: Unravelling effects of global change on disease in a vegetated coastal ecosystem

Human-induced global change seems to amplify the disease risk for terrestrial and marine biota. In the oceans, recent mass mortalities due to disease have affected many ecologically important species including corals, marine mammals and oysters. Higher marine plants, that form the foundation of many coastal ecosystems, thus supporting millions of people, are now also declining on a global scale. However, the role of diseases in these declines is yet unknown, especially if global change-promoted physiological stress enhances susceptibility to disease. Preliminary evidence suggests that changing environmental conditions may simultaneously increase pathogen development and survival. I therefore hypothesize that global change now amplifies the impact of diseases on marine plants, with large potential ecosystem consequences. Building on my previous work on a marine plant host-pathogen model that includes a member of a deadly group of plant diseases (Phytophthora spp.) and a widespread seagrass species (Zostera marina), I will assess: 1) how human-induced global change – specifically warming and nutrient enrichment (eutrophication) – affects the Zostera marina-Phytophthora gemini host-pathogen model system from plant to population level, and 2) how Phytophthora species infect Zostera spp. on a global scale. I will use a combination of field surveys, laboratory experiments, field monitoring and full life-cycle population modeling to investigate these objectives. The unique combination of proposed methods will allow me to develop a causal predictive model for the dynamics on the Zostera-Phytophthora host-pathogen system under global change. This will lay a foundation for the novel field of marine plant disease ecology, by addressing a number of key, now-emerging paradoxes on this topic. Unravelling mechanisms that support marine plant disease prevention and mitigation will strongly contribute to the conservation and restoration of vegetated coastal ecosystems worldwide.