CUR - The Council on Undergraduate Research

Temporal Variation in Eelgrass Wasting Disease Severity Alters Preferred Food Availability for Herbivores

Naomi Murray, Katherine DuBois, and Dr. Jay Stachowicz, Department of Evolution and Ecology, University of California - Davis, 1 Shields Ave, Davis, CA 95616

Eelgrass wasting disease has been responsible for multiple large die-offs of eelgrass (Zostera marina) over the last century, compromising critical habitat for fishes and invertebrates. Aside from these major outbreaks, little is known about the ecology of the disease, particularly regarding sub-lethal biotic interactions between the pathogen, seagrass, and epifaunal species. In this study, I measured the severity of wasting disease in Bodega Harbor and investigated whether disease alters plant susceptibility to herbivory. I found that disease severity varies seasonally; the necrotic lesions caused by eelgrass wasting disease were virtually absent in early summer but peaked at nearly 20% leaf cover by midsummer. This large fluctuation in the amount of decaying plant tissue may change food availability for herbivores of eelgrass. To determine if herbivores showed a preference for lesioned or green plant tissue, I conducted a series of feeding trials offering isopod Pentidotea resecata a choice between the two tissue types. Lesioned tissue was strongly preferred. Consistent with this preference, lesioned tissue required 45% less force to penetrate than green tissue, whereas plant nutritional quality (C:N ratio) and concentration of potential chemical defenses (phenolic acids) did not differ between the tissue types. Facilitation of herbivore feeding by disease could influence seasonal progression in disease severity, so understanding feedbacks between disease extent and herbivory may enhance our ability to predict the trajectory of eelgrass wasting disease outbreaks.

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