The world's oceans are in trouble on every measure that gets recorded: species loss, coral decline, pollution, acidification and rising temperature. Two remote parts of the Pacific are the exception, and a newly published survey sets out what has survived there.
The Bikar and Bokak atolls, which belong to the Marshall Islands, were declared the country's first national marine sanctuary last year. The study draws on a 2023 expedition.
What the survey found
Researchers recorded 266 kinds of reef fish across 38 families. Fish biomass — the total weight of fish present, which is a better measure of reef health than a species count alone — was higher at Bokak.
Using a submarine and deep-sea cameras, the team also identified fish in deeper water, including 14 groups that are new records for the Marshall Islands. Seventeen species of seabird were documented.
A reef with high fish biomass is one where large predators are still present. That is the first thing fishing removes, and it is why its presence is the clearest signal that a reef has been left alone.
Distance is the whole explanation
Bikar lies more than 100 kilometres from the nearest settlement. Bokak is roughly 400 kilometres away.
That is the finding, really. These ecosystems are not intact because of successful management, a conservation technique or a protected-area design worth copying. They are intact because getting to them is hard enough that not enough people have bothered.
It is worth being honest about what that means. The sanctuary designation protects a place that was already protected by geography. It is valuable — but it is not a method that can be applied to a reef near a city.
Even here, the damage arrived
The survey found signs of human interference anyway. Rats are present on the islands.
Rats reach remote islands on boats, and on seabird colonies they are devastating: they take eggs and chicks from ground-nesting species that evolved with no land predators at all. With 17 seabird species recorded, that is not a footnote. It is the one problem on these atolls that could be fixed, and eradication programmes on other Pacific islands have succeeded.
The atolls have also not escaped the global trends. Warmer water, coral bleaching and ocean acidification do not stop at a sanctuary boundary, and 400 kilometres of open sea is no defence against any of them.
Why a baseline like this is worth having
The practical value of surveying somewhere almost untouched is that it tells you what a damaged reef is supposed to look like.
Most marine science is done on reefs that were already degraded before anyone measured them, so "normal" gets quietly redefined downward with each generation of researchers. A site with intact fish biomass and deep-water species nobody had recorded before gives a reference point that is not just a memory.
For countries with their own reef systems under pressure — Bangladesh's narrow coastal and St Martin's reef habitat among them — that reference matters more than the headline species count. You cannot judge how far something has fallen without knowing where it started.
