Science and policy lessons learned from a decade of adaptation to the emergent risk of sargassum proliferation across the tropical Atlantic

Climatic and anthropogenic changes appear to be driving the emergence of new ecosystem and human health risks. As new risks emerge, and the severity or frequency of known risks change, we ask: what evidence is there of past adaptations to emergent risks? What scientific and policy processes lead to adaptive solutions that minimise the impacts of these events, and draw out opportunities? We identify science and policy lessons learned from coping with, and responding to, the sudden arrival of brown macroalgae (pelagic sargassum) that has proliferated across the tropical Atlantic since 2011. Drawing on an evidence base developed from a systematic search of literature relating to sargassum seaweed, and using event timelines and word clouds, we provide an analysis of lessons learned from a case study of adaptive responses across three continents to an emergent risk over the course of a decade. We reflect on successes and failures as well as opportunities taken in building adaptive capacity to address the risk in four key domains: policy, knowledge and evidence, monitoring and early warning, and technology and valorisation. Failures include: lack of environmental risk registries; missed opportunities to share monitoring data; and lack of a shared approach to manage the risk. Successes include: development of national management strategies; open-access knowledge hubs, networks and webinars sharing information and best practice; semi-operational early advisory systems using open access remote sensing data; numerous innovations customising clean-up and harvesting equipment, and research and development of new uses and value-added products.