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ActSmall · Ocean

What coverage measures (and what it hides)

“X% of the ocean is now protected” is a useful sentence and an easy one to misread. The dataset behind it is real, the methodology is documented, and the headline number obscures roughly four different things at once. Reading it well changes how the news reads.

Reading time: about seven minutes. ← back to the library

What an is, and what counts as one

A Marine Protected Area () is, in the ’s formal definition, “a clearly defined geographical space, recognised, dedicated and managed, through legal or other effective means, to achieve the long-term conservation of nature with associated ecosystem services and cultural values”[1]. The wording is broad on purpose: it has to accommodate everything from a fully no-take reserve in a single bay to a multi-use national-park-equivalent the size of a small country. The classifies protected areas across six management categories (Ia, Ib, II, III, IV, V, VI), with category Ia (strict nature reserve) the most restrictive and category VI (sustainable use of natural resources) the least[1][2].

Coverage statistics about the ocean are built from the World Database on Protected Areas (), jointly maintained by UNEP–WCMC and , and published through the public Protected Planet portal[2][3]. The is the canonical record of designated terrestrial and marine protected areas globally, including a separate marine layer (sometimes referred to as the - subset) used in the Protected Planet Reports. The dataset is updated on a rolling basis and was the basis of the previous Convention on Biological Diversity Aichi Target 11 (10% marine coverage by 2020) and the current Kunming–Montreal Global Biodiversity Framework Target 3, often shorthanded as “30 by 30” — 30% of land and 30% of marine areas effectively conserved by 2030[4].

versus territorial waters

National maritime jurisdiction is not a single number. (the United Nations Convention on the Law of the Sea) defines several concentric zones from the coastal baseline outward[5]:

  • Internal waters: the waters landward of the baseline (rivers, bays, ports). Full sovereignty.
  • Territorial sea: out to 12 nautical miles (~22 km) from the baseline. Coastal-state sovereignty, subject to innocent passage by foreign vessels. The phrase “territorial waters” in news coverage usually refers to this zone.
  • Contiguous zone: out to 24 nm. Limited enforcement rights for the coastal state.
  • Exclusive Economic Zone (): out to 200 nm. Sovereign rights over natural resources (fisheries, hydrocarbons, marine genetic resources), but not full sovereignty.
  • High seas / Areas Beyond National Jurisdiction (): everything outside any . Governed by the international community under and the 2023 Treaty (not yet in force at this writing).

An indicator of “% of marine area protected” depends entirely on which denominator is used. The World Bank indicator ER.MRN.PTMR.ZS, for instance, is “Marine protected areas (% of territorial waters)” — the 12 nm denominator[6]. The Protected Planet Reports typically report coverage as a share of national waters (-equivalent) and a separate share of global ocean (which includes the high seas). A country with extensive coastal protection but a vast will look very different on these two scales. Cross-reading is the safest habit: a single-figure “X% protected” without a denominator is incomplete.

Fully protected vs partially protected

The largest single source of confusion in statistics is that “protected” covers a wide range of permitted uses. The Guide, published in 2021 in Science by Grorud-Colvert and colleagues with backing from Marine Conservation Institute and partners, is the most-cited synthesis of how to disentangle this[7]. It describes four levels of protection:

  • Fully protected — no extractive or destructive activities allowed. Equivalent to “no-take.”
  • Highly protected — only minimal impact, light extractive uses (e.g. local non-commercial fishing) permitted.
  • Lightly protected — some commercial extraction permitted with limits.
  • Minimally protected — extensive use permitted; conservation benefit may be small.

The Guide also distinguishes stages of establishment — proposed, designated, implemented, actively managed — because the conservation outcome depends on the active-management stage, not on the legal designation.

The Marine Protection Atlas () maintained by Marine Conservation Institute is the most accessible public-facing layer that classifies MPAs by these levels and stages, complementing the ’s designation-based dataset[8]. The empirical literature on biological recovery inside MPAs — biomass, species richness, fish size structure — is consistently strongest in fully and highly protected areas; the effect attenuates substantially in lightly and minimally protected areas[7]. A coverage figure that does not separate these categories overstates conservation outcome.

The “paper parks” problem

An can be legally designated, mapped in the , counted in a national coverage figure, and yet have minimal management capacity, no compliance monitoring, no enforcement budget, and no measurable change in fishing pressure. The shorthand for this in the literature is “paper park”[9]. Paper parks are not unique to any one country — the gap between designation and effective management is documented across many regions, in both wealthy and low-income coastal states — but the consequence is the same: a coverage indicator that mixes well-managed MPAs with paper parks overstates ecological outcome relative to the headline figure.

Resources, governance, and surveillance are the three load-bearing variables in whether a designation translates into outcome. Modern remote-sensing tools have substantially narrowed the surveillance gap: Global Fishing Watch publishes near-real-time -based vessel tracking that allows researchers and journalists to document fishing activity inside nominally protected areas, which is the strongest public check on paper-park designations[10]. The dataset is open and the analytical workflow is increasingly accessible; this is a place where the public-data layer is genuinely catching up to the regulatory layer.

What coverage does not measure

The system is well-defined, and that is its strength. The corresponding limits are[7][9]:

  • It does not measure ecological outcome. Coverage is a proxy for protection, not an outcome metric. The outcome metric is biomass, richness, recruitment, habitat condition; those require sampling.
  • It does not capture enforcement. Whether the boundary is respected is a separate question. Vessel-tracking data and on-water enforcement budgets are the relevant inputs there.
  • It blends levels of protection. Fully protected areas do most of the conservation work; lightly and minimally protected areas do much less. The coverage figure typically lumps them together.
  • It is jurisdictional, not ecological. Marine ecosystems do not stop at boundaries. A migratory species can pass through dozens of jurisdictions in a year. National coverage describes a country’s decisions, not the ocean’s.
  • It does not yet count high-seas protection well. Until the Treaty enters into force and high-seas designations are operationalised under it, the “% of global ocean protected” figure is dominated by national-waters coverage. That will change in the coming years.

How to read a number

When a chart says “X% of country Y’s waters are protected,” the underlying questions are: Which denominator? Territorial waters (12 nm), (200 nm), or some other framing. What share is fully or highly protected? The Guide / layers separate this. What is the management stage? Designated and implemented are very different states. Is there independent compliance evidence? Vessel-tracking analyses and ecological surveys are the right complements to the designation figure.

The site you are reading exists in part because the gap between seeing a marine-protection figure and doing something about it is wider than it should be. The coverage number is a starting point, not a verdict.

Sources

  1. World Commission on Protected Areas — Protected Area Definition, Categories, and Marine Protected Area guidance. The formal definitions and management categories. https://www.iucn.org/our-work/topic/protected-areas-and-land-use
  2. UNEP-WCMC and — World Database on Protected Areas (). The canonical global dataset of designated protected areas, including the marine subset. https://www.protectedplanet.net/en/thematic-areas/wdpa
  3. UNEP-WCMC and — Protected Planet portal and the Protected Planet Report (Marine). Public access to coverage figures and methodology. https://www.protectedplanet.net/en
  4. Convention on Biological Diversity — Kunming-Montreal Global Biodiversity Framework, Target 3 (“30 by 30”). Adopted at COP15 in December 2022; the current global headline target. https://www.cbd.int/gbf/
  5. United Nations — United Nations Convention on the Law of the Sea (). The legal framework defining territorial waters, contiguous zone, , and high seas. https://www.un.org/depts/los/convention_agreements/texts/unclos/unclos_e.pdf
  6. World Bank Open Data — Marine protected areas (% of territorial waters), indicator ER.MRN.PTMR.ZS. The widely-used national-level coverage indicator, with a 12 nm denominator. https://data.worldbank.org/indicator/ER.MRN.PTMR.ZS
  7. Grorud-Colvert, K., Sullivan-Stack, J., Roberts, C., et al. (2021). The Guide: A framework to achieve global goals for the ocean. Science 373(6560): eabf0861. The widely-cited synthesis on levels of protection and stages of establishment. https://doi.org/10.1126/science.abf0861
  8. Marine Conservation Institute — Marine Protection Atlas (). Public-facing classification of MPAs by level of protection and management stage. https://mpatlas.org/
  9. Pieraccini, M., Coppa, S., De Lucia, G. A. (2017). Beyond marine paper parks? Regulation theory to assess and address environmental non-compliance. Aquatic Conservation 27(1): 177–196. Representative academic source on the paper-park concept. https://doi.org/10.1002/aqc.2632
  10. Global Fishing Watch — Open -based fishing-effort and vessel-tracking dataset. The most accessible public layer for assessing on-water activity inside MPAs. https://globalfishingwatch.org/

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