Invasive species as threat multipliers in freshwater ecosystems: biodiversity loss, interacting stressors, and management responses in the Anthropocene
Freshwater ecosystems occupy a small proportion of the Earth’s surface yetsupport exceptionally high biodiversity and essential ecosystem services. In theAnthropocene, these systems are increasingly threatened by interacting pressures, including hydrological alteration, land-use change, pollution, climatewarming, and biological invasions. This review examines invasive species as amajor driver of freshwater biodiversity loss between 2015 and 2026, whilesituating invasions within the broader multi-stressor context emphasized inrecent freshwater studies. Importantly, this review advances the concept ofinvasive species as “threat multipliers”, defined here as ecological agents thatnot only exert direct impacts but also amplify, reinforce, and prolong the effects ofco-occurring stressors such as climate change, eutrophication, and hydrologicaldisruption. This framing extends beyond traditional invasion ecology by explicitlylinking invasion processes to multi-stressor interaction theory. Evidence showsthat invasive fishes, macrophytes, decapods, and other ecosystem engineersreduce native biodiversity through competition, predation, habitat modification,food-web disruption, pathogen transfer, and biotic homogenization. Their impacts are often intensified by warming, nutrient enrichment, altered flow regimes,and other disturbances that facilitate establishment, spread, and ecologicaldominance. Where available, quantitative evidence demonstrates substantialecological and socio-economic consequences, including reductions in biodiversity indices, declines in ecosystem functioning, and measurable economic lossesassociated with degraded ecosystem services. In addition, invasions impairecosystem functioning and weaken ecosystem services by altering water clarity,nutrient cycling, habitat structure, fisheries productivity, and biomonitoring reliability. The review also highlights emerging responses, including eDNA-basedearly detection, prioritization frameworks, integrated control strategies, and the concept of functional eradication where complete removal is unrealistic.Major knowledge gaps remain in understanding multi-invader interactions,seasonal detectability, cross-ecosystem spillovers, long-term ecologicalchange, and climate-ready management, especially in underrepresentedregions such as Africa. This review provides both generalizable insights andregion-specific implications for biodiversity conservation and management inthe Anthropocene.