‘It just kept going’: Mega coral found at Cocos (Keeling) Islands

Résumé détaillé

Researchers have mapped a coral colony stretching over a record-breaking 1.56km along the outer reef of the remote Australian territory.

An extraordinary coral formation in the waters off Australia’s remote Cocos (Keeling) Islands has been revealed as one of the largest known coral colonies ever recorded.

The formation known locally as ‘the rose coral’ is estimated to cover approximately 56,940sq.m – roughly the equivalent size of the Sydney Opera House site.

Sections of the coral (Pachyseris sp.) were first discovered more than three decades ago by local dive operator Dieter Gerhard. “Over time, we established several dive sites along the outer reef and noticed large expanses of the rose coral along the deeper outer reef slope, but we didn’t know if these were all connected as one coral,” Gerhard said.

These early discoveries prompted researchers from Adelaide University, Queensland Museum and James Cook University to investigate the formation. Led by Dr Jean-Paul Hobbs from Adelaide University, the team embarked on a highly detailed underwater mapping exercise, spending months documenting the colony’s remarkable dimensions.

The mapping revealed a continuous formation stretching 1.56km and occupying the north-west outer reef slope at depths of between 14 and 65 metres, with an average width of 36.5m.

And the main colony may not even be the full extent of the story. Additional sections of rose coral extend a further 200 to 300 metres beyond its mapped boundaries, hinting at an even more extensive coral formation.

Measuring the formation proved to be an extraordinary undertaking. The coral is located on the outer edge of the atoll, and Dr Hobbs had to wait for suitable conditions. He originally tried to survey the area using the manta-tow method, where a diver holds a rope and is towed by a boat. But sharks became too inquisitive, so he switched to the manual approach of swimming out a measuring tape. Using this slower method, Dr Hobbs had to make repeated trips as the extent became apparent.

“It just kept going,” Dr Hobbs said. “I would swim along the reef measuring the coral but would run out of air…

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