The Baker test explosion.

Following World War II, the emergence of nuclear weapons became a subject of public fascination. Previous detonations had all been performed in complete secrecy or in the theater of war, and it wouldn’t be until 1946 that the general population was allowed to glimpse its first sight of an actual explosion as it happened. At Bikini Atoll, in the Marshall Islands of the Central Pacific, the US Navy first publicly detonated an atomic bomb near a grouping of decommissioned and captured ships to determine their ability to withstand such an assault. This was essentially a test to determine the viability of naval forces in the new atomic age, and the press was invited to watch.

Dubbed the Baker test, this 21 kiloton underwater explosion sent some two million gallons of water into the air, creating a mushroom cloud some 6000 feet in height and 2000 feet across. Shortly following this explosion, a tsunami reaching 90 feet in height formed as water rushed to fill the void momentarily created by the blast. Finally, as the expelled water began to fall back to into the ocean, a radioactive mist spread out in all directions, enveloping the heavily damaged vessels.

Ten ships were sunk by the Baker test, with most of the remainder proving to be rendered so radioactive that they would also be sunk. Naively, military officers had planned on sailing these vessels away following this test, only to be thwarted by the unanticipated mist which contaminated everything near the blast radius. It took an unusual experiment from an army colonel overseeing the radiation cleanup to finally persuade the navy to abandon their ships.

The radioactive surgeonfish of Bikini Atoll. Possibly Acanthurus triostegus?

Dr. Stafford Warren collected an apparently healthy surgeonfish from the shallow lagoon and left it resting atop a piece of photographic film. In the morning, the fish had left an X-ray from the radiation it had released, with a particularly heavy amount emanating from its gut contents. And so the US Navy was finally convinced that their ships were best discarded.

Clearly, there was a massive environmental catastrophe created underwater at Bikini Atoll, but there doesn’t appear to have been any study of the immediate aftermath. This was, of course, an era long before SCUBA became a regular part of ecological research. But the effects would linger long afterwards. A German ship called the Prinz Eugen was heavily damaged but failed to sink. It was eventually towed to nearby Kwajalein, where it would finally submerge some six months later.

Scrubbing radiation from the Prinz Eugen.

I’m not sure what the rationale was for this relocation, but it turns out that we are quite literally paying the consequences to this day. The condition of the ship and its final resting location have amounted to a “worst case scenario” for Kwajalein. Around 2700 tons of oil are still on-board this deteriorating vessel, which is increasingly shifting and collapsing. The risk of a major spill in this delicate ecosystem is so high as to be a certainty. And this is why, in 2014, the US Fish & Wildlife Service made a financial assessment for preemptively drilling into the ship’s holding tanks and extracting the oil. The estimate for the procedure is some $3-4 million, which is comparable to the estimated cost of cleaning up a major oil spill from this lagoon.

There were many more nuclear tests conducted in the Marshall Islands, some of which had their own disastrous results. The Castle Bravo test of 1954 was the first to use a hydrogen bomb. Its explosion proved to be three times as powerful as had been anticipated and sent radioactive ash drifting through several nearby island communities. A Japanese fishing boat sailing through the region had its crew stricken with acute radiation syndrome, with reports of some playfully licking the strange ash which had fallen onto their boat. One fisherman would die of liver damage a few months after. When the boat arrived in Japan, some of the 400+ tons of fish on-board even made it to market. The vessel now resides in a Tokyo museum.

A map of radioactive fish collected after the Castle Bravo test. Arrows show major water currents.

While the US Navy tried to downplay the radioactive fallout from this event, Japanese scientists monitored the contamination present in the catches of commercial fishermen. The map present above originates from a Japanese study from this time, and gives a fascinating insight into the ocean currents in this region and the connectivity between these seemingly distant islands. It’s particularly interesting to see so many of these radioactive fish present in the Ryukyu Arc of Japan, as the coral reef fish communities of this region show relatively little direct similarity to those of Micronesia. However, these distinct ecoregions are still well connected by the equatorial currents, and it would seem that the larger pelagic fish collected by these fisherman spread much further than the more sedentary reef fish fauna aquarists are familiar with.

As a coda to this sad story, the people of the Marshall Islands have suffered more than anyone. Aside from instances of acute radiation poisoning, these people have had to live with the lingering presence of radiation throughout their lives. While the levels are deemed safe now, the cancer rate for much of the population is significantly higher than normal, with one estimate placing it near 100 times what is typical. The US Government has spent hundreds of millions of dollars in settlements, and ultimately gave possession of this island group back to its people in the 1970’s in conjunction with this compensation. There is still strong sentiment amongst the Marshallese that the health and environmental damage caused by these nuclear tests has yet to be adequately redressed.

Nuclear weapons won’t stop the Rhomboid Wrasse & Tracey’s Damselfish. Credit: Gary Parr & Dave Burdick

But despite the catastrophe wrought by all this human folly, the coral reefs of Kwajalein and Bikini Atolls have remained remarkably resilient. There are still a great many Cirrhilabrus rhomboidalis and Chrysiptera traceyi swimming these reefs. So the next time you see one of these fishes in an aquarium, don’t forget that its ancestors had to survive atomic bombs.