Disease Analysis in San Juan Archipelago

The role of disease in San Juan Archipelago eelgrass (Zostera marina) decline: An untested but potentially serious problem.

Funded by the WWW Foundation

Co-PI’s: J. K. Gaydos (University of California at Davis), S. Wyllie-Echeverria (FHL, UW), A. Boettcher and Dan Martin (University of South Alabama)

In 2003 and 2004, relatively rapid decline of Z. marina meadows was observed at several sites in the San Juan Archipelago, a prominent feature of the Salish Sea sub-region of the Pacific Northwest. Cause for these declines is still the subject of investigation, however, even though the pathogen known to bring about a disease epidemic exists in the San Juan Archipelago, the possibility that acute loss was the result of a disease event has not been thoroughly tested.

Microogranisms of the genus Labyrinthula are the most notable disease agents. Once infected a leaf can spread the disease to other leaves, lethally infecting a large area. Past studies suggest two or three species are present on leaves but only one “pathogenic” form (L. zosterae) has been described. The description of this form was based on cell size, shape and re-infection assays. In contrast, investigation using a molecular barcoding approach suggests at least five strains/species of Labyrinthula are present on Z. marina leaves, several of which may lead to an infectious disease outbreak. Paralleling, at least one of these phylotypes is pathogenic, with the four other phylotypes has yet to be assayed for pathogenicity.

Overall estimates of maximum diversity for Labyrinthula have not yet been attempted. Documenting Labyrinthula diversity and associating particular strains with Z. marina declines requires intensive sampling followed by virulence testing of the isolated strains. Therefore, we designed a project to investigate in detail two geographically adjacent sites with varying Z. marina genetic diversity and population stability, followed by four additional sites sampled less intensively, providing much-needed information on the diversity and distribution of this opportunistic pathogen. We will transfer results of our investigation and a program designed to determine sites at risk from a disease outbreak to federal, state and county agencies responsible for natural resource management.