Fifty years ago, Bikini Atoll was used for major atom bomb testing. Surprisingly, the huge blasts and massive radiation did not destroy all life. Corals are flourishing.

The tiny atoll in the North Pacific, one of the Marshall Islands, was the test site for American atom bombs during the late 1940s and 1950s, including the most powerful American atom bomb ever exploded.

The Bravo bomb was 15 megatonnes - a thousand times more powerful than the bomb dropped on Hiroshima.

It vapourised three islands, raised water temperatures to 55,000 degrees, shook islands 200 kilometres away and left a crater two kilometres wide and 73 metres deep.

Now an international team of marine scientists from Australia, Germany, Italy, Hawaii and the Marshall Islands have examined Bikini Atoll and reported on the diversity and abundance of marine life found there.

Diving into Bravo Crater

One of the most interesting aspects was the amount and diversity of coral forms the team members found when they dived into Bravo Crater.

After diving into the crater, Dr Zoe Richards of the Australian Research Council’s Centre of Excellence for Coral Reef Studies and James Cook University, said she hadn’t known what to expect – “some kind of moonscape perhaps.

"But it was incredible, huge matrices of branching Porites coral up to eight metres high had established, creating thriving coral reef habitat.

"Throughout other parts of the lagoon it was awesome to see coral cover as high as 80 per cent and large tree-like branching coral formations with trunks 30cm thick. It was fascinating – I've never seen corals growing like trees outside of the Marshall Islands.”

She said the healthy condition of the coral at Bikini atoll today is proof of their resilience and ability to bounce back from massive disturbances, so long as the reef is left undisturbed and there are healthy nearby reefs to seed the recovery.

Not all Corals Survived

However, the expedition showed that not all corals survived the massive atomic blasts.

Compared with a famous study made in the early 1950s before the biggest atomic tests were carried out, the team established that 42 species were missing.

At least 28 of these species losses appear to be genuine local extinctions probably due to the 23 bombs that were exploded there from 1946-58, or the resulting radioactivity, increased nutrient levels and smothering from fine sediments, Dr Richards said.

“The missing corals are fragile lagoonal specialists – slender branching or leafy forms that you only find in the sheltered waters of a lagoon,” she said.

While the corals in general have shown resilience, it was clear that the coral biodiversity at Bikini Atoll had proven only partially resilient to the huge disturbances of the 1940s and 50s.

World Heritage Listing Sought

Because of its incredible history and current undisturbed character, Bikini Atoll is now part of a larger project to have northern Marshall Island atolls World Heritage-listed.

Apart from occasional forays of illegal fishing boats after shark, tuna and Napoleon Wrasse, the reef is almost completely undisturbed to this day.

There are very few local inhabitants, and the divers who visit, dive on shipwrecks, like the USS Saratoga, and not on the reef,

The expedition showed that the tragic history of the Bikinian people is not entirely reflected below the surface because, although the reefs of Bikini are recovering as havens of abundance to the marine life of the Northern Pacific Ocean, the island itself is uninhabitable.

While there are only low levels of gamma radiation on the land – “pretty much like the background radiation in an Australian city” - local produce such as coconut is unsafe to eat because of the high levels of radioactive materials accumulated from the soil.

It is unlikely that people will ever be able to return to live on the island.

“Ironically, thanks to the bombs, Bikini Atoll represents a priceless laboratory showing how, in the absence of ongoing stress, some corals have the capacity to recover from vast upheavals,” Dr Richards said.

“It may contain valuable lessons for the management of reefs in other parts of the world, including Australia.”

The team's report on Bikini corals surviving atom bombs appears in Elsevier's Marine Pollution Bulletin No. 56, March 2008.

See also: New Species of Angler Fish Found