Challenging the paradigms of deep-sea ecology

•Deep-sea ecosystems represent Earth's major ecological research frontier.•New discoveries challenge past ecological hypotheses and paradigms.•These new findings provide new views of deep-sea ecology.•Deep-sea exploration has entered a new golden age. Deep-sea ecosystems represent Earth's major ecological research frontier. Focusing on seafloor ecosystems, we demonstrate how new technologies underpin discoveries that challenge major ecological hypotheses and paradigms, illuminating new deep-sea geosphere–biosphere interactions. We now recognize greater habitat complexity, new ecological interactions and the importance of ‘dark energy’, and chemosynthetic production in fuelling biodiversity. We also acknowledge functional hotspots that contradict a food-poor, metabolically inactive, and minor component of global carbon cycles. Symbioses appear widespread, revealing novel adaptations. Populations show complex spatial structure and evolutionary histories. These new findings redefine deep-sea ecology and the role of Earth's largest biome in global biosphere functioning. Indeed, deep-sea exploration can open new perspectives in ecological research to help mitigate exploitation impacts.