Latitudinal variation in seagrass wasting disease from Puget Sound to Alaska

Widely regarded as critical marine habitat, seagrass provides ecologically and economically valuable services in coastal areas worldwide. Eelgrass (Zostera marina) is one of five seagrass species native to the Pacific Northwest and is threatened by outbreaks of the marine protist Labyrinthula zosterae, the causative agent of seagrass wasting disease. Infection from L. zosterae causes necrotic lesions, limiting growth and compromising the health of eelgrass beds. To determine levels of wasting disease in subtidal eelgrass beds across a broad latitudinal gradient, we measured and compared disease prevalence and severity in 5 subtidal eelgrass beds in Puget Sound, 5 in the San Juan Islands, 4 on Calvert Island, British Columbia, and 4 in south eastern Alaska. Disease prevalence, the proportion of diseased blades to health blades, was highest in Puget Sound, and steadily decreased in sites further north. Severity, the proportion of diseased tissue to healthy tissue on infected blades, also varied between sites and geographic regions. To determine potential environmental drivers of disease across broad spatial scales, we also measured site characteristics: density, canopy height, water temperature, and salinity. Understanding broad-scale patterns of disease and environmental drivers of wasting disease outbreaks can inform key decisions regarding eelgrass conservation within and beyond the Salish Sea