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With the continuous growth of global demand for marine spatial resources, three-dimensional layered utilization of sea areas is important to understand in order to resolve conflicts in marine development and support the growth of the blue economy. However, current research on this topic has primarily focused on theoretical and policy discussions, and there is no systematic method for assessing the vertical compatibility of sea use activities. To address this issue, we adopt a research approach that combines theoretical construction and expert evaluation. First, the theoretical foundation of three-dimensional marine development is analyzed across three dimensions – spatial, elemental (functional elements such as ships and marine infrastructure), and temporal. This is done to clarify the spatial usage characteristics of sea use activities and their mechanisms of interaction across different dimensions. Then, we construct an analytical framework to assess the vertical compatibility of marine activities. Using expert scoring results, this framework follows a stepwise process that sequentially evaluates spatial dependency, the nature of functional components, and temporal conflicts. We also incorporate environmental factors for supplementary adjustments, which enable the derivation of a vertical compatibility matrix for marine activities. The results indicate: (1) Regarding the spatial dimension, based on the degree of spatial dependence of sea use activities on the water surface, water column, seabed, and subsoil, their occupied space can be divided into main space and ancillary space. Sea use activities sharing the same main space are vertically incompatible. (2) From the elemental dimension, the stronger the rigidity of an activity's functional components, the lower its compatibility potential. (3) In terms of the temporal dimension, even short-term occupation of marine space for construction or maintenance can cause spatial conflicts. (4) From an environmental perspective, some activities can affect vertical compatibility with other activities by damaging the environment and/or reducing safety. (5) The vertical compatibility between sea use activities can be categorized into three types: fully compatible, conditionally compatible, and incompatible. This study provides a logical micro-level description of the characteristics of sea use activities in marine space, presenting a vertical compatibility matrix that covers many current types of sea use activities. It also analyzes application objectives, application pathways, and potential implications for public policy. The findings may act as reference material for international marine spatial planning, use regulation, multi-use ocean management, and related policymaking, thereby contributing to modern marine spatial governance systems.
Xu et al. (Sat,) studied this question.