New type of reef identified in the Kimberley

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The remote Kimberley coast is characterised by its extreme tidal ranges, warm turbid waters and frequent cyclonic events, and is also home to a newly recognised form of coral reef, one which grows higher than any other reef type in the world.

Curtin University researcher Dr Mick O’Leary has been leading a Western Australian Marine Science Institution (WAMSI) project team that’s been characterising the surface morphology and internal architecture of Kimberley coral reefs using mutlibeam sonar and seismic profiling technologies, as well as collecting reef cores to establish growth histories and ecological change on thousand year time scales.

The findings, published in the journal Coral Reefs, provide new insights into the ability of Kimberley corals to survive, endure, and thrive, in what is generally considered to be environmentally challenging conditions for coral growth.

The seismic profiling revealed that the living coral veneer does not represent simple coral communities growing on rock foundations but are in fact the surface expression of massive and complex reef structures comparable to what we might see at Ningaloo or the Abrolhos or even the Great Barrier Reef.

Percussion coring on Bathurst-Irvine Island, core length up to six metres were recovered using this method. (Mick O’Leary)

The research team drove 6.5 metre lengths of aluminium tubing into the reef structure to recover a record of reef growth. Radiocarbon dating of corals collected from reef cores revealed that coral growth commenced in the Kimberley almost immediately after the continental shelf was flooded by rising sea levels that followed the end of the last ice age some 12 to 15 thousand years ago, with the oldest dated inshore corals returning ages of more than 9000 years.

The most unusual feature of Kimberley reefs is the elevation of their reef flats. Typically coral reefs will grow vertically until they reach sea level, then having used up all the available vertical space, they switch growth directions and begin to grow laterally into deeper water. The upper vertical limit of reef growth is the mean low water tide level, as corals can only tolerate exposure to the atmosphere for brief periods, which usually occurs around spring low tides.

However, the team’s multibeam sonar surveys have precisely measured the elevation of the reef flats and revealed that Kimberley reefs have grown vertically through the mean low water level limit up to the mean tide level.

“This basically means the corals on the reef flat spend half their life exposed above the level of the tide,” Dr O’Leary said. “The sight of water cascading off the edges of a Kimberley coral reef as the tide falls is something that you can experience nowhere else on Earth.”

Somehow Kimberley corals have managed to adapt over many thousands of years to these extreme tidal ranges, high levels of turbidity, really warm water temperatures and exposure, and are thriving in the Kimberley despite these conditions.

So as we see the beginnings of yet another major bleaching event on the Great Barrier Reef, we might look to these more robust Kimberley coral reefs and ask what is unique about these corals? How long did it take to adapt to the unique Kimberley marine environments and are there lessons here that can be applied to the more sensitive coral reef regions of the world?

Water cascading off the reef at Tallon Island (Tubagus Solihuddin)

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The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government’s Kimberley Science and Conservation Strategy co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley.

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Kimberley Marine Research Program