What giant pumice raft could mean for reef in FNQ

A RAFT of volcanic pumice the size of Paris is floating faithfully towards the Australian coastline - but it may not be the coral-hitchhiking lifeline to the Great Barrier Reef it is cracked up to be.

Global media have heralded the island of floating rock spotted near Tonga as a potential godsend for the Reef.

Michael Hoult from SailSurfROAM encountered a giant pumice raft while sailing near Tonga. PICTURE: SUPPLIED
Michael Hoult from SailSurfROAM encountered a giant pumice raft while sailing near Tonga. PICTURE: SUPPLIED

However ARC Centre of Excellence for Coral Reef Studies director Professor Terry Hughes said the possibility of corals catching a ride to replenish the gene pool was unlikely to eventuate.

"If you pick up a piece of pumice on the beach, it's usually pretty clean," he said.

"You can occasionally find baby corals on them but most corals don't settle on something that's bobbing around on the surface of the ocean.

"They prefer something more solid and deeper."

There is also issue over how a clingy baby coral would find its way off the buoyant rocks and onto the Reef below.

Normanby Island is brimming with sea life including coral, fish and crustaceans as a resilient and bustling part of the Great Barrier Reef in Far North Queensland. PICTURE: JULIANA RESTREPO VILLEGAS
Normanby Island is brimming with sea life including coral, fish and crustaceans as a resilient and bustling part of the Great Barrier Reef in Far North Queensland. PICTURE: JULIANA RESTREPO VILLEGAS

"It would have to grow big and old enough on the pumice to then reproduce a new generation of larvae that made its way onto the Reef," Prof Hughes said.

"That would take an awfully long time.

"In theory, it could be a mechanism for delivering baby corals but it would take three to four years before they started to reproduce.

"I'm not aware of anyone showing it could happen."

Normanby Island is brimming with sea life including coral, fish and crustaceans as a resilient and bustling part of the Great Barrier Reef in Far North Queensland. PICTURE: JULIANA RESTREPO VILLEGAS
Normanby Island is brimming with sea life including coral, fish and crustaceans as a resilient and bustling part of the Great Barrier Reef in Far North Queensland. PICTURE: JULIANA RESTREPO VILLEGAS

It is a spectacular sight for sailors who stumble across the phenomenon - about 150 square kilometres of rock on the ocean's surface, covering an area about as big as Paris.

But in the context of the 344,000 square kilometre Great Barrier Reef, it is barely a pinprick

"Presumably it will break up as it moves," Prof Hughes said.

"In the meantime there are still plenty of corals left on the Reef that survived the two bleaching events, and they are reproducing."

Normanby Island is brimming with sea life including coral, fish and crustaceans as a resilient and bustling part of the Great Barrier Reef in Far North Queensland. PICTURE: JULIANA RESTREPO VILLEGAS
Normanby Island is brimming with sea life including coral, fish and crustaceans as a resilient and bustling part of the Great Barrier Reef in Far North Queensland. PICTURE: JULIANA RESTREPO VILLEGAS

Pumice raft

Very light and extremely porous rock formed during explosive volcanic eruptions when the gas-rich froth of glassy lava solidifies rapidly.

Depending on its porosity, it can become waterlogged and eventually sink - but this could take a matter of years, which is likely to be longer than the Tongan pumice raft will take to hit the Australian coastline and was ashore.

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