• Energy Research

151 pages ; Supplemental file(s) description: Graham Supplemental Material. ; In nature, interactions between a pathogen, susceptible host, and a suite of environmental conditions can influence disease transmission and spread. Here, I examine the impacts of the environment and microbial and herbivore communities on disease dynamics in Pacific Northwest eelgrass (Zostera marina). This is an especially tractable and important system for exploring these questions, given that the causative agent of seagrass wasting disease, Labyrinthula zosterae, is temperature-sensitive and culturable and given the value of eelgrass meadows and the ecosystem services they provide.In Chapter 1, I used a combination of field and lab approaches to explore the impact of wasting disease on eelgrass growth and belowground sugar reserves in natural eelgrass meadows. In Chapter 2, I examine the role of the eelgrass microbiome—bacteria and Archaea living on the surface of eelgrass leaves—in defense against disease. In Chapter 3, I conducted field surveys to determine how disease varies with depth and different environmental conditions. In Chapter 4, I used a range of experimental approaches to understand the role of eelgrass herbivores in disease transmission. Collectively, this work provides a deeper understanding of factors that influence disease dynamics in eelgrass meadows. As eelgrass are marine sentinels, indicative of the health of our oceans, understanding which factors influence disease spread and levels in nature can better inform the conservation and management of these valuable marine foundation species.

151 pages ; Supplemental file(s) description: Graham Supplemental Material. ; In nature, interactions between a pathogen, susceptible host, and a suite of environmental conditions can influence disease transmission and spread. Here, I examine the impacts of the environment and microbial and herbivore communities on disease dynamics in Pacific Northwest eelgrass (Zostera marina). This is an especially tractable and important system for exploring these questions, given that the causative agent of seagrass wasting disease, Labyrinthula zosterae, is temperature-sensitive and culturable and given the value of eelgrass meadows and the ecosystem services they provide.In Chapter 1, I used a combination of field and lab approaches to explore the impact of wasting disease on eelgrass growth and belowground sugar reserves in natural eelgrass meadows. In Chapter 2, I examine the role of the eelgrass microbiome—bacteria and Archaea living on the surface of eelgrass leaves—in defense against disease. In Chapter 3, I conducted field surveys to determine how disease varies with depth and different environmental conditions. In Chapter 4, I used a range of experimental approaches to understand the role of eelgrass herbivores in disease transmission. Collectively, this work provides a deeper understanding of factors that influence disease dynamics in eelgrass meadows. As eelgrass are marine sentinels, indicative of the health of our oceans, understanding which factors influence disease spread and levels in nature can better inform the conservation and management of these valuable marine foundation species.

Seagrass meadows provide valuable ecosystem benefits but are at risk from disease. Eelgrass (Zostera marina) is a temperate species threatened by seagrass wasting disease (SWD), caused by the protist Labyrinthula zosterae. The pathogen is sensitive to warming ocean temperatures, prompting a need for greater understanding of the impacts on host health under climate change. Previous work demonstrates pathogen cultures grow faster under warmer laboratory conditions and documents positive correlations between warmer ocean temperatures and disease levels in nature. However, the consequences of disease outbreaks on eelgrass growth remain poorly understood. Here, we examined the effect of disease on eelgrass productivity in the field. We coupled in situ shoot marking with high-resolution imagery of eelgrass blades and used an artificial intelligence application to determine disease prevalence and severity from digital images. Comparisons of eelgrass growth and disease metrics showed that SWD impaired eelgrass growth and accumulation of non-structural carbon in the field. Blades with more severe disease had reduced growth rates, indicating that disease severity can limit plant growth. Disease severity and rhizome sugar content were also inversely related, suggesting that disease reduced belowground carbon accumulation. Finally, repeated measurements of diseased blades indicated that lesions can grow faster than healthy tissue in situ. This is the first study to demonstrate the negative impact of wasting disease on eelgrass health in a natural meadow. These results emphasize the importance of considering disease alongside other stressors to better predict the health and functioning of seagrass meadows in the Anthropocene.

Seagrass meadows provide valuable ecosystem benefits but are at risk from disease. Eelgrass (Zostera marina) is a temperate species threatened by seagrass wasting disease (SWD), caused by the protist Labyrinthula zosterae. The pathogen is sensitive to warming ocean temperatures, prompting a need for greater understanding of the impacts on host health under climate change. Previous work demonstrates pathogen cultures grow faster under warmer laboratory conditions and documents positive correlations between warmer ocean temperatures and disease levels in nature. However, the consequences of disease outbreaks on eelgrass growth remain poorly understood. Here, we examined the effect of disease on eelgrass productivity in the field. We coupled in situ shoot marking with high-resolution imagery of eelgrass blades and used an artificial intelligence application to determine disease prevalence and severity from digital images. Comparisons of eelgrass growth and disease metrics showed that SWD impaired eelgrass growth and accumulation of non-structural carbon in the field. Blades with more severe disease had reduced growth rates, indicating that disease severity can limit plant growth. Disease severity and rhizome sugar content were also inversely related, suggesting that disease reduced belowground carbon accumulation. Finally, repeated measurements of diseased blades indicated that lesions can grow faster than healthy tissue in situ. This is the first study to demonstrate the negative impact of wasting disease on eelgrass health in a natural meadow. These results emphasize the importance of considering disease alongside other stressors to better predict the health and functioning of seagrass meadows in the Anthropocene.

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’.

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’.

Significance Consumption transfers energy and materials through food chains and fundamentally influences ecosystem productivity. Therefore, mapping the distribution of consumer feeding intensity is key to understanding how environmental changes influence biodiversity, with consequent effects on trophic transfer and top–down impacts through food webs. Our global comparison of standardized bait consumption in shallow coastal habitats finds a peak in feeding intensity away from the equator that is better explained by the presence of particular consumer families than by latitude or temperature. This study complements recent demonstrations that changes in biodiversity can have similar or larger impacts on ecological processes than those of climate.