Bikini Atoll, in the northern Marshall Islands, was the site of 23 nuclear weapons tests conducted by the United States between 1946 and 1958. The Bikinian population — approximately 167 people at the time of the first test — was relocated by the US military in 1946 and has not returned. The atoll has been functionally uninhabited for nearly eight decades.
The same is broadly true of Enewetak Atoll, where a further 43 nuclear tests were conducted in the same period, and of several other locations in the northern Marshall Islands. The atolls remain technically Marshallese territory; the indigenous populations remain legally recognised as the proper inhabitants. The radiological legacy of the testing programme remains contested, complicated, and the subject of continuing legal claims by Marshallese citizens against the United States. None of which is the subject of this piece.
What this piece is about is what has happened to the marine ecosystems of these atolls in the decades during which no humans have been present to fish them.
The scientific work has been led by researchers at the Scripps Institution of Oceanography, the University of California Santa Barbara, and several Marshallese-affiliated institutions. The most recent surveys, conducted across multiple expeditions through the 2010s and into the early 2020s, have documented marine ecosystems that bear almost no resemblance to comparable atoll systems elsewhere in the Pacific.
The reef fish biomass measured at Bikini and Enewetak is among the highest recorded anywhere in the world. Apex predator densities — particularly sharks — are at levels consistent with what scientists describe as a “pristine” reef ecosystem, a state most reef systems left in the modern era. The reefs themselves are structurally robust, with coral cover, three-dimensional complexity, and species diversity comparable to the most protected reference sites globally.
The picture is not uncomplicated. The sites carry detectable radioactive isotope signatures in some species. The reef ecosystems show the long-term effects of the actual physical destruction caused by the tests, including persistent craters in some locations. The atolls' marine systems are not pristine in any absolute sense. What they demonstrate is what reef ecosystems become when they are released from the specific pressure of human fishing for several human generations.
The implication, for marine conservation policy globally, is structurally significant. The recovery documented at Bikini and Enewetak occurred in spite of substantial radiological and physical insult — challenges far more severe than the absence of fishing pressure faced by any normal marine protected area. The systems recovered anyway. The dominant driver of reef-ecosystem health, the data suggests, is the presence or absence of fishing pressure, with most other factors operating at the margins.
The atolls have also become, almost by accident, a baseline. They are among the only locations on the planet where scientists can study Pacific reef ecosystems unaffected by industrial-era fishing. The data from Bikini and Enewetak now anchors a substantial fraction of the global research on what reefs should look like, and on what they could look like elsewhere if pressure were removed.
The Marshallese government continues to negotiate the long-term future of these atolls — including questions of resettlement, decontamination, and the legal status of the marine areas surrounding them. The scientific access to the sites depends on those negotiations. What has been learned to date will, regardless of how those negotiations resolve, continue to inform marine recovery work across the Pacific and beyond.