In a study published in Ecology, a team led by Prof. XU Jun from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences, and collaborators from Peking University, University of Essex and Huazhong Agricultural University, uncovered a novel mechanism by which climate warming impedes the recovery of submerged plants through intensified herbivory during insect outbreaks.

The researchers conducted a large-scale mesocosm experiment using 48 outdoor ponds (each 2500 L) to simulate shallow lake ecosystems under ambient and warmed conditions (+3.5°C with simulated heatwaves). During the experiment, an unexpected outbreak of the aquatic moth Parapoynx diminutalis provided a unique opportunity to examine how warming interacts with insect outbreaks to affect aquatic plants. 

The results showed that warming advanced plant phenology, leading to an earlier growth peak in spring. However, they showed that the outbreak of moth larvae was much more severe under warmed conditions. The increased larval density, particularly on the dominant plant species Hydrilla verticillata, enhanced grazing pressure and drastically reduced plant biomass and regenerative capacity.

The loss of aquatic plants released nutrients into the water column, promoting phytoplankton blooms and shifting the ecosystem from a clear-water, macrophyte-dominated state to a turbid, algae-dominated state. This transition was more pronounced under warming where higher concentrations of total nitrogen, total phosphorus, and phytoplankton chlorophyll a were recorded.

The study highlights the risk of coupled extreme climate and population outbreak events, and underscores the need to account for climate-mediated biotic interactions in predicting and managing freshwater ecosystem stability. It suggests that preventive measures such as introducing small insectivorous fish should be considered in aquatic plant restoration experiments.