World's rarest coral spotted for the first time in over 100 yearsS

Covering 30% of Earth's surface and totaling 622 million cubic kilometers, the Pacific Ocean still holds countless secrets. But even so, oceanographers weren't expecting to find this - supposedly extinct elkhorn coral, spotted for the first time since the 1890s.

The coral was discovered - or, more accurately, rediscovered - during an underwater survey of the Arno Atoll, a remote part of the North Pacific country the Marshall Islands. What we call "coral" is actually a massive colony of microscopic creatures that band together into what looks like a single organism. This particular colony has been classified Acropora rotumana. As part of the Acropora genus, it is one of the main types of coral that builds its distinctive reefs.

The elkhorn coral colonies - so named because they create branches like elk antlers - were up to 16 feet wide and 7 feet high, which is unusually big for coral. Their size indicates that the colonies are also very old - although individual corals only live a couple years, the colonies as a whole can live for decades or even centuries, and the elkhorn probably falls into the century category.

According to survey leader Zoe Richards of the Centre of Excellence for Coral Reef Studies in Queensland, Australia, it's amazing just how unusual these coral colonies are: "When I first saw it, I was absolutely stunned. [The coral colonies]were like nothing I'd seen before in the Pacific Ocean. So far I have only found this new population of coral to occur along a small stretch of reef at a single atoll in the Marshalls group. It grows in relatively shallow water along the exposed reef front and, so far, fewer than 200 colonies are known from that small area."

The coral fits the description of coral spotted off the coast of Fiji in the 1898. Unfortunately, those colonies are now gone, and there isn't enough genetic information left to confirm that they're a match. In any event, now that we've rediscovered this particular coral species, our immediate goal is simply to preserve it. With so few colonies found, which would easily place it among the world's rarest types of corals. Its Atlantic counterpart, also known as the elkhorn coral, is singled out as the worst victim of coral destruction in the Caribbean. The Atlantic elkhorn is critically endangered, and its reefs have disappeared from much of the Caribbean over the past few decades.

Coral geneticist David Miller of CoECRS and Queensland's James Cook University, echoes the incredible nature of the find, and notes that it just as much reminds us what we don't know as adds to what we do know:

"When Zoe showed me pictures of the Pacific elkhorn, I was shocked. The colonies look just like the critically endangered Caribbean species A. palmata, one of the most distinctive of all corals. The fact that these colonies might represent a species that has not been seen for over a hundred years (A. rotumana) says something about how much we know about the remote reefs of the North Pacific."

[Systematics and Biology]