Deeper habitats and cooler temperatures moderate a climate-driven seagrass disease

Eelgrass creates critical coastal habitats worldwide and fulfills essential ecosystem functions as a foundation seagrass. Climate warming and disease threaten eelgrass, causing mass mortalities and cascading ecological impacts. Subtidal meadows are deeper than intertidal and may also provide refuge from the temperature-sensitive seagrass wasting disease. From cross-boundary surveys of 5761 eelgrass leaves from Alaska to Washington and assisted with a machine-language algorithm, we measured outbreak conditions. Across summers 2017 and 2018, disease prevalence was 16% lower for subtidal than intertidal leaves; in both tidal zones, disease risk was lower for plants in cooler conditions. Even in subtidal meadows, which are more environmentally stable and sheltered from temperature and other stressors common for intertidal eelgrass, we observed high disease levels, with half of the sites exceeding 50% prevalence. Models predicted reduced disease prevalence and severity under cooler conditions, confirming a strong interaction between disease and temperature. At both tidal zones, prevalence was lower in more dense eelgrass meadows, suggesting disease is suppressed in healthy, higher density meadows. These results underscore the value of subtidal eelgrass and meadows in cooler locations as refugia, indicate that cooling can suppress disease, and have implications for eelgrass conservation and management under future climate change scenarios.This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Automated summary

Eelgrass is a vital seagrass that plays a crucial role in creating important coastal habitats and fulfilling essential ecosystem functions worldwide. The warming climate and diseases pose a threat to eelgrass, causing mass mortalities and ecological impacts. Subtidal meadows, which are deeper than intertidal areas, may provide refuge from temperature-sensitive diseases. A study involving cross-boundary surveys and a machine-language algorithm found that disease prevalence was 16% lower in subtidal leaves compared to intertidal leaves. Cooler conditions were associated with lower disease risk in both tidal zones. Despite being more environmentally stable, subtidal meadows still exhibited high disease levels, highlighting the interaction between disease and temperature. The study also revealed that dense eelgrass meadows had lower disease prevalence, implying the importance of maintaining healthy and dense meadows for disease suppression. These findings emphasize the value of subtidal eelgrass and cooler locations as refuges, demonstrate the potential of cooling to suppress disease, and have implications for eelgrass conservation and management in the face of future climate change scenarios.