Coral found out of depth stirs intrigue
EXCLUSIVE A SHALLOW water coral found thriving at 110m on the Great Barrier Reef has scientists stunned at how the species is able to survive at such an extreme depth.
A team of researchers has discovered a branching coral (Acropora) growing at Holmes Reef, about 250km east of Cairns, during a recent survey of coral biodiversity in the northern Great Barrier Reef and western Coral Sea.
The discovery, published in scientific journal Marine Biodiversity, sets a new record for the group of reef-building corals, which have previously only been found at maximum depths between 40-60m.
Acroporas – also known as staghorn corals – are commonly found in shallow reef areas where there is plenty of sunlight so that their symbiotic algae can convert to food.
However, lead researcher, Museum of Tropical Queensland coral collection manager Dr Paul Muir, said the team had been amazed to find the coral Acropora tenella thriving over a large area at an extreme depth.
“We found some corals down at about 125m, and they were a particular type of specialised deepwater coral,” he said.
“They were these stunted little things, about 5-10cm in diameter, whereas this coral at 110m was a huge bank of coral, about 20 sqm in area, which is pretty amazing.
“You kind of think of everything down there to be very restricted in terms of light, and right on the edge of distribution, whereas this thing was thriving.
“It’s possible that this species goes even deeper in other places.”
He believed that due to proximity to the equator, and the clarity of water, there was far more sunlight penetrating the depths where the coral was found. However it is not yet known whether the species possesses the same photosynthetic algae (zooxanthellae), like its shallow-water relatives, allowing it to convert the sun’s rays into energy.
“We haven’t actually looked inside the tissues yet, but they have the right colour,” he said. “Basically if corals have that coffee-brown colour to them, that means that they’ve got zooxanthellae in them, and basically the staghorn corals – to date, anyway – are only recorded as having zooxanthellae. It would be unusual to find them without it.”
He said researchers were hoping to return to the site later this year.
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