ESA Ecology article of the week: The potential of zooplankton in constraining chytrid epidemics in phytoplankton hosts

Hi everyone, this is the third Ecology journal article of the week! As always, I’ve pulled up an open access article from the Ecology journal. I thought they had more frequent featured articles, but apparently not, so using that isn’t going to work every week. This was the first open access article from the current issue that I came across. I decided to do this rather than picking someone that I personally found interesting, just so we can have as wide of a range of ecology articles as possible.

You can find the open access link here: https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecy.2900?campaign=wolearlyview

Please feel free to discuss this article in the comments below if you like. Questions, comments, or anything remotely relevant is fair game!



Abstract:

Fungal diseases threaten natural and man‐made ecosystems. Chytridiomycota (chytrids) infect a wide host range, including phytoplankton species that form the basis of aquatic food webs and produce roughly half of Earth’s oxygen. However, blooms of large or toxic phytoplankton form trophic bottlenecks, as they are inedible to zooplankton. Chytrids infecting inedible phytoplankton provide a trophic link to zooplankton by producing edible zoospores of high nutritional quality. By grazing chytrid zoospores, zooplankton may induce a trophic cascade, as a decreased zoospore density will reduce new infections. Conversely, fewer infections will not produce enough zoospores to sustain long‐term zooplankton growth and reproduction. This intricate balance between zoospore density necessary for zooplankton energetic demands (growth/survival), and the loss in new infections (and thus new zoospores) because of grazing was tested empirically. To this end, we exposed a cyanobacterial host (Planktothrix rubescens) infected by a chytrid (Rizophydium megarrhizum) to a grazer density gradient (the rotifer Keratella cf. cochlearis). Rotifers survived and reproduced on a zoospore diet, but the Keratella population growth was limited by the amount of zoospores provided by chytrid infections, resulting in a situation where zooplankton survived but were restricted in their ability to control disease in the cyanobacterial host. We subsequently developed and parameterized a dynamical food‐chain model using an allometric relationship for clearance rate to assess theoretically the potential of different‐sized zooplankton groups to restrict disease in phytoplankton hosts. Our model suggests that smaller‐sized zooplankton may have a high potential to reduce chytrid infections on inedible phytoplankton. Together, our results point out the complexity of three‐way interactions between hosts, parasites, and grazers and highlight that trophic cascades are not always sustainable and may depend on the grazer’s energetic demand.