Transmission Pathways of Seagrass Wasting Disease in Coastal Meadows

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Warming in the oceans caused by climate change increases the risk of disease outbreaks in valuable marine organisms and habitats. Seagrass meadows in temperate waters are vital habitats, affected globally by Eelgrass Wasting Disease. This is a devastating disease, known to increase with warming, and is already outbreaking locally along the US west coast. The team’s work over the last decade documents significant declines in eelgrass meadows and outbreaks of wasting disease in the Salish Sea, WA. A combined laboratory, field, and modeling program will transform our understanding of how eelgrass wasting disease epidemics are initiated and transmitted in nature. To communicate the combined risk of disease with climate change and the ways disease spreads in the ocean, the team runs hands-on K-12 programs with Padilla Bay National Estuarine Research Reserve, the Friday Harbor Laboratories K-12 program and the Spring Street School Salish Sea School. The team will continue a 5-week graduate course at Friday Harbor Laboratories to train the next generation of disease ecologists and develop a documentary film, Epidemics Rising in the Seagrass.The transmission mode used by a pathogen to move between hosts is poorly understood for most marine diseases. Outbreaks of eelgrass wasting disease, caused by the marine protozoan Labyrinthula zosterae, occurs on Pacific shores from California to Alaska, with intermittent outbreaks. Quantitative estimates of the rates and extent of waterborne and multiple modes of transmission are knowledge gaps limiting understanding of marine disease processes. Experimental studies reveal a circulating portfolio of L. zosterae strains varying in virulence and genetics from non-pathogenic to extremely pathogenic and transmitted by both contact and through the water. Experiments show that disease is transmitted by dual transmission modes of contact and waterborne, as is common, but poorly documented, for many marine pathogens. To understand the transmission pathways that underlie the spread of the disease, the team will first measure the role of factors including warming and pathogen strain in starting new infections. Secondly, the team is investigating how both resident microbiomes and biota such as grazing snails and filtering oysters can affect the rate of new infections. Thirdly, the results from lab experiments are applied to a whole meadow setting to help the team model the way the disease spreads in nature. This study system allows direct, experimentally verified incorporation of species interactions into the disease transmission model, including the role of microbiome, invertebrate vectors and filter feeders.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.