Effects of Climate Change on Eelgrass Wasting Disease

Climate change affects the health of marine organisms. Ocean acidification (OA) and rising water temperature can alter species interactions, extend organisms beyond their physiological optima and thus are predicted to increase infectious disease events. When disease impacts ecosystem engineers, community level change is possible. Eelgrass, Zostera marina, are ecosystem engineers providing ecosystem services including carbon sequestration and local mitigation of OA. Eelgrass wasting disease (WD), caused by infection from the opportunist pathogen, Labyrinthula zosterae, can be associated with rapid population declines of Z. marina. We conducted two experiments to determine the influence of OA and increased water temperature (separately) on the presence and severity of the WD. In the first, we grew Z. marina under three C0₂ conditions, 400, 800, and 1600 ppm, to represent current, 'bad day' and 'future' climate scenarios. After acclimation to these conditions, half the treatments were exposed to L. zosterae. In the high CO₂, low pH water, the proportion of diseased Z. marina leaves decreased when compared to leaves in the low CO₂, high pH water. In a second experiment, Z. marina adults and seedlings were allowed to acclimate to low (11° C), high (18° C) and fluctuating (between 11 and 18° C) water temperatures and then half these individuals were exposed to L. zosterae. Disease occurred more rapidly and with higher severity in seedlings and at high and fluctuating temperatures. Further analyses will allow us to quantify Labyrinthula load, and production of potential host defenses (total phenols and condensed tannins) among these samples. Our results suggest that host-pathogen relationships for this system will be altered in changing climatic conditions and that further research is needed to understand how climate change influences community resilience and ecosystem system services provided by eelgrass meadows.