Developing achievable alternate futures for key challenges during the UN Decade of Ocean Science for Sustainable Development.

The oceans face a range of complex challenges for which the impacts on society are highly uncertain but mostly negative. Tackling these challenges is testing society's capacity to mobilise transformative action, engendering a sense of powerlessness. Envisaging positive but realistic visions of the future, and considering how current knowledge, resources, and technology could be used to achieve these futures, may lead to greater action to achieve sustainable transformations. Future Seas (www.FutureSeas2030.org) brought together researchers across career stages, Indigenous Peoples and environmental managers to develop scenarios for 12 challenges facing the oceans, leveraging interdisciplinary knowledge to improve society's capacity to purposefully shape the direction of marine social-ecological systems over the UN Decade of Ocean Science for Sustainable Development (2021-2030). We describe and reflect on Future Seas, providing guidance for co-developing scenarios in interdisciplinary teams tasked with exploring ocean futures. We detail the narrative development for two futures: our current trajectory based on published evidence, and a more sustainable future, consistent with the UN's Sustainable Development Goals, which is technically achievable using existing and emerging knowledge. Presentation of Business-as-usual and More Sustainable futures-together-allows communication of both trajectories, whilst also highlighting achievable, sustainable versions of the future. The advantages of the interdisciplinary approach taken include: (1) integrating different perspectives on solutions, (2) capacity to explore interactions between Life Under Water (Goal 14) and other SDGs, and (3) cross-disciplinary learning. This approach allowed participants to conceptualise shared visions of the future and co-design transformative pathways to achieving those futures. Supplementary Information SI: The online version contains supplementary material available at (10.1007/s11160-020-09629-5) contains supplementary material, which is available to authorized users.