I have a clear memory of the first time I understood, viscerally, what a marine protected area feels like from underwater.
I had been diving a stretch of reef in the Philippines that was technically protected but effectively unmanaged, plastic on the sand, crown-of-thorns starfish unchecked across the tables, fish skittish and small, the reef itself looking exhausted. Two days later I dove a neighbouring area that had been under strict no-take protection for twelve years, enforced by a community of former fishermen who patrolled it themselves. The difference was not subtle. There were Napoleon wrasse. There were bumphead parrotfish in a school of thirty, moving across the reef like a slow tide. There were sharks.
Same ocean. Same depth. Twelve years apart in management.
What the Evidence Shows
The science on marine protected areas is now extensive and largely consistent. A 2021 meta-analysis in Science, drawing on data from 1,800 MPAs worldwide, found that fully protected areas contain, on average, 600% more biomass than unprotected areas nearby. Fish are larger, more numerous, and represent a more complete range of species, including apex predators, which are the first to disappear when fishing pressure increases.
Spillover is real. Fish and invertebrates move across MPA boundaries into adjacent fishing grounds, improving catches for fishers who operate near well-managed reserves. A study of community-managed MPAs in the Philippines found that fishers within 500 metres of a protected area caught significantly more per trip than those fishing further away. The MPA, far from taking something away, was subsidising the fishery around it.
Beyond fisheries, fully protected areas show higher coral cover, greater structural complexity, and more resilience to bleaching events. Herbivorous fish, parrotfish, surgeonfish, graze algae from coral, preventing the algal overgrowth that follows bleaching. When these fish are abundant, reefs recover faster. When they are absent, algae win.
The Gap Between Paper Parks and Real Protection
The global target set at COP15 in Montreal in 2022 is to protect 30% of the world’s oceans by 2030. This is sometimes called 30x30. As of 2024, approximately 8% of the ocean has some form of protected status. Of that, less than 3% is highly or fully protected.
The distinction matters enormously. A marine protected area that allows fishing, anchoring, and industrial development is what conservationists call a paper park: it exists on a map and in a legal instrument but provides little biological benefit. The MPA designation can even be harmful if it creates a false impression of protection, redirecting conservation attention while damage continues.
Effective MPAs share a small number of characteristics, identified repeatedly in the literature: they are no-take for fishing; they are old enough to have accumulated biomass (at least a decade of protection); they are well-enforced; they are isolated enough that fishing pressure on their borders does not undermine the interior; and they have community buy-in, particularly from fishers who understand and accept the boundaries.
That last point is not rhetorical. The most effective MPAs in the world are not necessarily government-run. Many of the best-performing reserves in the Philippines, Indonesia, and Fiji are managed by local fishing communities with a direct economic stake in the reef’s health. When the fishers are the wardens, enforcement is consistent and local violations are rare.
Shark Sanctuaries
Sharks are among the most valuable indicator species in a marine ecosystem and among the most threatened. An estimated 100 million sharks are killed by fishing each year, for fins, for meat, as bycatch. Shark populations globally have declined by over 70% since 1970, with some species down by 90% or more.
Shark sanctuaries, national waters where shark fishing is prohibited, now cover roughly 13 million square kilometres across 17 countries, including the Maldives, Palau, the Bahamas, and the Marshall Islands. Within these areas, and within fully protected MPAs more broadly, shark populations show clear signs of recovery.
Diving in a shark sanctuary feels different. Not just because there are sharks, though there are, but because of what their presence signals. Sharks structure the ecosystem beneath them. When they hunt, they concentrate prey species in ways that create feeding opportunities for other predators. Their absence creates a cascade of effects down the food web, most of which are bad for the reef and bad for fisheries.
Palau is often cited as the clearest example. For a closer look at what reef recovery actually looks like, read about Cabo Pulmo’s 463% biomass recovery, the strongest documented case for no-take reserves anywhere in the world. Its no-take marine reserve, established in 2015, covers 80% of its Exclusive Economic Zone, about 500,000 square kilometres. Early monitoring showed rapid recovery of shark populations and improved catch rates in the remaining fishing zones. The economic case was also straightforward: a single reef shark, alive in the water, generates an estimated $1.9 million in tourism revenue over its lifetime. Dead, it is worth around $108 for its fins.
The 30x30 Question
Reaching the 30x30 target with meaningful, enforced protection requires a scale of political will and resource allocation that currently does not exist. Most MPAs are underfunded. Enforcement technology, satellite monitoring, drone patrol, automatic identification systems for vessels, is available but expensive. In many of the countries where protection is most needed, budgets for marine enforcement are minimal. Ghana’s declaration of its first MPA in 2026, built around 21 coastal fishing communities from the outset, is a recent example of what first-time designation looks like in practice, and what it requires to have any chance of working.
The High Seas Treaty, adopted by the United Nations in 2023 after twenty years of negotiation, provides a legal mechanism for creating MPAs in international waters for the first time. This is significant: approximately 64% of the ocean lies beyond national jurisdiction and has historically been almost entirely ungoverned. The treaty still requires ratification and implementation by member states, but it is a genuine structural advance.
The ocean’s capacity for recovery, given space and time, is not in question. The question is whether we will provide the space and the time. Every MPA established, funded, and enforced is a direct answer. It does not solve climate change. It does not stop plastic. But it keeps the ecosystem intact long enough for those other battles to be won or lost.
That is worth something. In some parts of the ocean, right now, it is worth everything.
