The “open ocean” has become a highly contested space as coastal populations and maritime uses soared in abundance and intensity over the last decades. Changing marine utilization patterns represent a considerable challenge to society and governments. Maritime spatial planning has emerged as one tool to manage conflicts between users and achieve societal goals for the use of marine space; however, single-sector management approaches are too often still the norm. The last decades have seen the rise of a new ocean use concept: the joint “multi-use” of ocean space. This paper aims to explain and refine the concept of ocean multi-use of space by reviewing the development and state of the art of multi-use in Europe and presenting a clear definition and a comprehensive typology for existing multi-use combinations. It builds on the connectivity of uses and users in spatial, temporal, provisional, and functional dimensions as the underlying key characteristic of multi-use dimensions. Combinations of these dimensions yield four distinct types of multi-use with little overlap between them. The diversity of types demonstrates that there is no one-size-fits-all management approach, but rather that adaptive management plans are needed, focusing on achieving the highest societal benefit while minimizing conflicts. This work will help to sharpen, refine and advance the public and academic discourse over marine spatial planning by offering a common framework to planners, researchers and users alike, when discussing multi-use and its management implications.

Marine spatial planning (MSP) processes seek to better manage ocean spaces by balancing ecological, social and economic objectives using public and participatory processes. To meet this challenge, MSP approaches and tools have evolved globally, from local to national scales. At two International Marine Conservation Congresses (2016 and 2018), MSP practitioners and researchers from diverse geographic, technical and socio-economic contexts met to share advances in practical approaches and spatial tools to achieve multi-objective MSP. Here we share the lessons learned and commonalities that emerged from studies conducted in Belize, Canada, South Africa, Seychelles, the United Kingdom and the United States on a number of topics related to advancing MSP. We identify seven important themes that we believe are broadly relevant to any multi-objective MSP process: (1) indigenous and local knowledge should inform planning goals and objectives; (2) transparent and evidence-based approaches can reduce user conflict; (3) simple ecosystem service models and scenarios can facilitate multi-objective planning; (4) trade-off analyses can help balance diverse objectives; (5) ecosystem services may assist planning for high value-data poor Blue Economy sectors; (6) game theoretic decision rules can help to deliver fair, equitable and win–win spatial allocation solutions; and (7) strategic mapping products can facilitate decision making amongst stakeholders from different sectors. Some of these themes are evident in MSP processes that have been completed in the previous decade, but the fast-evolving field of MSP is addressing increasingly more complex objectives, and practitioners need to respond with practical approaches and spatial tools that can address this complexity.

Transboundary conservation has an important, yet often undervalued, role in the international conservation regime. When applied to the legally ambiguous and interconnected marine environment this is magnified. The lack of clear guidance for transboundary marine conservation from the international conservation community exacerbates this problem, leaving individual initiatives to develop their own governance arrangements. Yet, well-managed transboundary marine protected areas (MPAs) have the potential to contribute significantly to global conservation aims. Conversely, in a period where there is increasing interest in marine resources and space from all sectors, the designation of MPAs can create or amplify a regional conflict. In some instances, states have used MPAs to extend rights over disputed marine resources, restrict the freedom of others and establish sovereignty over maritime space. Six case studies were taken from Europe, North Africa and the Middle East to illustrate how states have interpreted and utilized different legislative mechanisms to either come together or diverge over the governance of marine resources or maritime space. Each of the case studies illustrates how different actors have used the same legislative tools, but with different interpretations and applications, to justify their claims. It is clear that the role of science combined with a deeper engagement with stakeholders can play a critical role in tempering conflict between states. Where states are willing to cooperate, the absence of clear guidelines at the global level means that often ad hoc measures are put into place, with the international frameworks then playing catch up. Balancing different jurisdictional claims with the conservation of the marine environment, whilst considering the increasing special economic interests will become increasingly difficult. Developing a transboundary conservation tool, such as the simple conservation caveats found in the Barcelona Convention and Antarctic Convention, which allow for the establishment of intergovernmental cooperation without prejudicing any outstanding jurisdictional issue, would provide a framework for the development of individual transboundary MPAs.