Interaction between climate change scenarios and biological invasion reveals complex cascading effects in freshwater ecosystems

Climate change often facilitates biological invasions, leading to
potential interactive impacts of these global drivers on freshwater
ecosystems. Although climatic mitigation efforts may reduce the magnitude
of these interactive impacts, we are still missing experimental evidence
for such effects under multiple climate change scenarios within a
multi-trophic framework. To address this knowledge gap, we experimentally
compared the independent and interactive effects of two climate change
scenarios (mitigation and business-as-usual) and biological invasion on
the biomass of major freshwater trophic groups (phytoplankton,
zooplankton, periphyton, macroinvertebrates, and a native macrophyte) and
the decomposition rate of allochthonous material. Among the independent
effects, we found that the business-as-usual climate treatment resulted in
lower native macrophyte biomass and higher periphyton biomass compared to
the climatic baseline and mitigation treatments. This indicates the
potential of climate change to alter the relative dominance of different
freshwater producers and demonstrates that climate mitigation efforts can
counteract these effects. Biological invasion alone increased the biomass
of chironomids, a dominant macroinvertebrate group in tropical freshwater
ecosystems, demonstrating a compensatory effect on climate change. Climate
change and biological invasion interactively reduced the decomposition
rate of allochthonous detritus, likely mediated by the feeding preference
of abundant chironomids for periphytic algae associated with the presence
of non-native macrophytes. We concluded that (i) climatic mitigation can
maintain climate baseline conditions in freshwater ecosystems, and (ii)
the interactive effects between future climate scenarios and biological
invasion are related to complex cascading interactions among trophic
groups on ecosystem processes.