Variation in eelgrass wasting disease severity affects consumption patterns and preferred food availability for an eelgrass herbivore

Link To Share This Poster: https://cdmcd.co/Rrm9Qq
Live Discussion Link: https://cdmcd.co/PJ9xXj

Naomi Murray, University of California, Davis, Katie DuBois, Bodega Marine Lab, UC Davis, Bodega Bay, CA and John J. Stachowicz, Department of Evolution and Ecology, University of California, Davis, Davis, CA

Background/Question/Methods
Eelgrass wasting disease has been responsible for multiple die-offs of eelgrass (Zostera marina) over the last century, compromising critical habitat for fishes and invertebrates. Despite major outbreaks, little is known about the ecology of the disease, particularly regarding sub-lethal interactions between the pathogen, seagrass, and epifaunal species. In this study, I measured the severity of eelgrass wasting disease in Bodega Harbor and investigated whether disease alters plant susceptibility to herbivory. To assess disease severity in the field, I recorded the extent of necrotic wasting disease lesions on plants along a single transect throughout the summer. To determine if herbivores showed a preference for lesioned or green plant tissue, I conducted feeding trials offering isopod Pentidotea resecata a choice between the two tissue types. I also collected data on lesioned and green tissue traits, like chemical defense levels (phenolic acid content), to consider potential drivers of observed consumption patterns.
Results/Conclusions
I found that disease severity varies seasonally; 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. The feeding trial showed that lesioned tissue was strongly preferred over green tissue; on average, lesioned tissue accounted for nearly 70% of an herbivore’s total consumption. I used structural equation modeling to further relate plant trait data to observed feeding preferences. As plant lesion cover increased, the phenolic acid content of lesion tissue decreased. Phenolic acids are a potential chemical deterrent of herbivores, and the loss of phenolics was associated with increasing herbivore consumption. This facilitation of herbivore feeding by disease may influence seasonal progression in disease severity. Understanding feedbacks between disease extent and herbivory may improve our ability to predict the trajectory of eelgrass wasting disease outbreaks.