Ecological interactions amplify cumulative effects in marine ecosystems.

Biodiversity encompasses not only species diversity but also the complex interactions that drive ecological dynamics and ecosystem functioning. Still, these critical interactions remain overwhelmingly overlooked in environmental management. In this study, we introduce an ecosystem-based approach that assesses the cumulative effects of climate change and human activities on species in the St. Lawrence marine ecosystem, eastern Canada, by explicitly accounting for the effects arising from species interactions within a multiple stressors framework. Our findings reveal previously unrecognized threats to exploited and endangered fishes and marine mammals, exposing noteworthy gaps in existing management and recovery strategies. By integrating the less obvious yet no less substantial effects arising from species interactions into cumulative effects assessments, our approach provides a robust tool to guide more comprehensive and effective management and conservation efforts for marine species.