Wildfire effects on aquatic host-parasite interactions

AbstractIncreases in the intensity and frequency of wildfires highlight the need to understand how fire disturbance affects ecological interactions. Though the effects of wildfire on free-living aquatic communities are relatively well-studied, how host-parasite interactions respond to fire disturbance is largely unexplored. Our study investigated the effects of wildfire on trematode parasites and their intermediate snail hosts using a Before-After-Control-Impact design. We surveyed 10 stream sites (5 burned and 5 unburned) in the Willamette River Basin, Oregon and quantified host infection status and trematode community structure one year before and two years after historic wildfires. Despite the severity of the wildfires, snail host populations appeared resilient, without significant shifts in population characteristics. We detected nine taxa of trematode parasites and overall prevalence of infection remained consistent over the three-year study period. However, at the taxon-specific level, we found evidence that infection probability by one trematode decreased and one increased after fire. In a larger dataset focusing on the first year after fire (9 burned, 8 unburned sites), we found evidence for subtle differences in trematode community structure, including higher Shannon diversity and evenness at the burned sites. Taken together, our results suggest that host-parasite interactions were remarkably stable for most taxa; for trematodes that did show responses, changes in abundance or behavior of definitive hosts that input infectious stages to the aquatic environment may underlie observed patterns. These results provide a useful first step in evaluating the broader utility of parasites as bioindicators of ecosystem changes following wildfire disturbance.