1,000-year-old monstrosity in Indian Ocean: Scientists map 100-buses-long giant coral

Scientists have discovered a coral colony 1.5 kilometres long in the middle of the Indian Ocean, which is believed to be one thousand years old. It is sitting on the edge of an atoll, near the remote Cocos Islands and is a rose coral, belonging to the genus Pachyseris. For context, the colony is equal to 100 buses parked one behind the other. The coral colony is unlike anything scientists have seen in the past.

Pachyseris colonies normally span about 6.4 feet in diameter. So to find one that is 4,921 feet wide is truly shocking and mesmerising at the same time. It also goes as deep as 45 to 213 feet in different places. Despite the coral colony being first seen about 30 years ago, it was only recently studied in great detail by marine biologist and SCUBA diver JP Hobbs.

Dieter Gerhard, a dive operator based at the Cocos Islands, was the first one to come across the mammoth coral. Hobbs told ScienceAlert that he explored the first dive site, and then went back two more times. But the colony kept going. "I was just waiting for the end, and the end never came," he said. It took Hobbs a total of 12 dives to map out the entire coral colony.

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Hobbs believes that the coral colony could have stretched up to two kilometres in the past. He saw the Pachyseris continuing on the other side of a 10-metre gap, which shows that it was actually even bigger at one time and the reef presumably crumbled where it ends today. Hobbs collected coral specimens from 50 different points, which have been sent to the Queensland Museum where marine geneticist Peter Cowman will study them.

One larva or individual colonies?

Through the analysis, scientists will try to determine whether it belongs to a known Pachyseris species or if it is an entirely new group. Cowman added that another mystery they will try to solve is whether this entire colony comes from one genetically identical organism, "a tiny larva that settled there and grew into this monstrosity that we've now mapped," or whether they are "individual colonies that could be closely related" and fused over time.

Both of them are exceptionally rare occurrences, meaning this finding is incredible either way. If what we have is many clones of one organism, the colony could be hundreds or thousands of years old. "I think if it is one single individual, it might be one of the largest corals that has been found," Cowman said.

The reason this colony grew to be so large is because of the rows of concentric plate-like structures. "If a fragment falls down the slope a bit, and then begins to grow from that fragment, and then it merges with the main colony, that's still the same individual, but it's expanding its range," Cowman said. Scientists are now looking forward to see if the colony's size can help it survive the changing climate.