Networks in Aquatic Communities Collapse Upon Neonicotinoid-Induced Stress

Freshwater ecosystems worldwide are under pressure from neonicotinoid insecticides. While it is recognised that communities of species are responsible for ecosystem functioning, it remains unknown if neonicotinoid-induced community transformations negatively affect ecosystem functioning. Therefore, we employed an experimental approach with 36 naturally established freshwater ecosystems exposed to increasing field-realistic concentrations of the neonicotinoid thiacloprid. Upon exposure, we found severe degradation of ecosystem functioning in the form of loss of organic matter consumption and dramatic shifts in primary productivity. This functional decline coincides with strongly eroded species co-occurrence networks to the point that these are indistinguishable from randomised assemblages of species. Together, these findings show how current environmental concentrations of a neonicotinoid can strongly disrupt freshwater ecosystem functioning via degradation of the invertebrate food web. Since this dramatic ecosystem degradation occurs below nearly all identified ecotoxicological risks, we call here for the reconsideration of the use of these insecticides.