Ecological interactions amplify cumulative effects in marine ecosystems

Abstract The Convention on Biological Diversity is setting ambitious goals for preserving biodiversity, the first of which states that the integrity of ecosystems must be enhanced. This recognizes that biodiversity is not a mere collection of species; it also includes the diversity of interactions driving ecological dynamics and ecosystem functioning. Yet management still overwhelmingly operates in silos, focusing on single stressor and species. Here, we assess the cumulative effects of climate change and human activities on species of the St. Lawrence marine ecosystem in eastern Canada using a novel approach that explicitly considers the web of interactions structuring communities. We uncover cumulative effects that would otherwise be overlooked if species interactions were ignored, particularly for fishes and marine mammals, many of which are exploited or endangered. This suggests that management plans and recovery strategies may be ignoring significant threats by overlooking species interactions. Our approach is, to our knowledge, the first ecosystem-based approach relevant to the management of exploited and endangered species which can evaluate the less obvious yet no less significant effects arising from species interactions in a multiple stressors framework.