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<p>The global ocean faces an unprecedented triple planetary crisis—climate change, biodiversity loss, and systemic pollution—exacerbated by fragmented governance frameworks. In&#xa0;Particular, the absence of a universally recognized boundary separating coastal and marine environments has perpetuated fragmented governance, ecological mismanagement, and policy ambiguities. Existing legal frameworks, including the United Nations Convention on the Law of the Sea (UNCLOS), define maritime zones primarily by jurisdictional sovereignty rather than ecological function, leaving shelf-sea ecosystems under weak or overlapping management. This misalignment creates "governance vacuums," particularly in the outer continental shelf of the Global South, where Marine Spatial Planning (MSP) remains nascent and confined up to 12 NM. This paper proposes a science-based spatial threshold, a 50-nautical-mile (NM) boundary from the baseline, to distinguish coastal from marine environments, aligning governance with ecological, oceanographic, and geochemical realities. Drawing from global evidence on bathymetry, productivity gradients, species distributions, and human impacts, the 50-NM threshold captures critical transitions associated with the continental shelf, where over 80% of marine biodiversity, fisheries, and ecosystem services are concentrated. By formalizing this boundary, the paper introduces a three-zone governance framework: coastal zone (0–12 NM), transition zone (12–50 NM), and marine environment (beyond 50 NM). This approach strengthens spatial coherence in marine spatial planning, supports ecosystem-based management, and addresses legal gaps under existing regimes like UNCLOS and Convention on Biological Diversity (CBD). Legal and policy pathways for integrating the threshold include leveraging Article 194(5) of UNCLOS, expanding MPAs under the CBD, and embedding the delineation into national and regional frameworks. Pilot implementation opportunities in regions such as the Coral Triangle and Bay of Bengal illustrate its potential to enhance conservation effectiveness, facilitate transboundary cooperation, and advance sustainable blue economy outcomes. Critically, this threshold is presented not as a revision of sovereign maritime zones, but as a functional management unit designed to reduce jurisdictional fragmentation. By defining the 12–50-NM band as a "Transition Zone" of shared responsibility and high-intensity monitoring, coastal states can more effectively implement ecosystem-based management. Our analysis suggests that adopting this 50-NM threshold provides the necessary spatial resolution needed&#xa0;to protect migratory corridors, manage land-based pollutant plumes, and enhance climate resilience, providing a pragmatic blueprint for sustainable ocean governance in the Anthropocene. We conclude that the 50-NM ecological boundary is more than a technical delineation; it represents a transformative governance&#xa0;tool for realigning global ocean governance with ecological realities—enhancing biodiversity protection, strengthening climate resilience, and securing sustainable futures for coastal communities and marine ecosystems.</p>

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Redefining coastal and marine boundaries through a 50-NM functional threshold for integrated ocean governance

  • 期刊论文

  • 发表日期：

    2026年4月16日

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  • P. Ragavan,
  • R. Ramesh,
  • Sundeep,
  • K. Kathiresan,
  • P. M. Mohan

摘要

The global ocean faces an unprecedented triple planetary crisis—climate change, biodiversity loss, and systemic pollution—exacerbated by fragmented governance frameworks. In Particular, the absence of a universally recognized boundary separating coastal and marine environments has perpetuated fragmented governance, ecological mismanagement, and policy ambiguities. Existing legal frameworks, including the United Nations Convention on the Law of the Sea (UNCLOS), define maritime zones primarily by jurisdictional sovereignty rather than ecological function, leaving shelf-sea ecosystems under weak or overlapping management. This misalignment creates "governance vacuums," particularly in the outer continental shelf of the Global South, where Marine Spatial Planning (MSP) remains nascent and confined up to 12 NM. This paper proposes a science-based spatial threshold, a 50-nautical-mile (NM) boundary from the baseline, to distinguish coastal from marine environments, aligning governance with ecological, oceanographic, and geochemical realities. Drawing from global evidence on bathymetry, productivity gradients, species distributions, and human impacts, the 50-NM threshold captures critical transitions associated with the continental shelf, where over 80% of marine biodiversity, fisheries, and ecosystem services are concentrated. By formalizing this boundary, the paper introduces a three-zone governance framework: coastal zone (0–12 NM), transition zone (12–50 NM), and marine environment (beyond 50 NM). This approach strengthens spatial coherence in marine spatial planning, supports ecosystem-based management, and addresses legal gaps under existing regimes like UNCLOS and Convention on Biological Diversity (CBD). Legal and policy pathways for integrating the threshold include leveraging Article 194(5) of UNCLOS, expanding MPAs under the CBD, and embedding the delineation into national and regional frameworks. Pilot implementation opportunities in regions such as the Coral Triangle and Bay of Bengal illustrate its potential to enhance conservation effectiveness, facilitate transboundary cooperation, and advance sustainable blue economy outcomes. Critically, this threshold is presented not as a revision of sovereign maritime zones, but as a functional management unit designed to reduce jurisdictional fragmentation. By defining the 12–50-NM band as a "Transition Zone" of shared responsibility and high-intensity monitoring, coastal states can more effectively implement ecosystem-based management. Our analysis suggests that adopting this 50-NM threshold provides the necessary spatial resolution needed to protect migratory corridors, manage land-based pollutant plumes, and enhance climate resilience, providing a pragmatic blueprint for sustainable ocean governance in the Anthropocene. We conclude that the 50-NM ecological boundary is more than a technical delineation; it represents a transformative governance tool for realigning global ocean governance with ecological realities—enhancing biodiversity protection, strengthening climate resilience, and securing sustainable futures for coastal communities and marine ecosystems.