Don’t count your corals before they attach

A giant pumice “raft” is floating across the Pacific Ocean towards Australia, raising hopes it could restock the Great Barrier Reef, which suffered unprecedented bleaching events in 2016 and 2017. 

We should perhaps temper our optimism, however. There are some logistical issues.

About the size of Manhattan, the pumice was created following an underwater volcanic eruption near Tonga.

It is expected to travel via New Caledonia, Vanuatu and the reefs in the eastern Coral Sea before arriving in Australia in about seven months from now – perhaps bringing with it new healthy corals and other reef dwellers.

It is currently bare and barren, but it’s hoped new organisms will jump on board and flourish during the journey.

That’s possible but unlikely, says Terry Hughes, director of Australia’s ARC Centre of Excellence for Coral Reef Studies, because such things are pretty rare. {%recommended 8872%}

“Pumice floats, and corals don’t like to attach to something that’s bobbing around on the ocean,” he says.

“Usually when a baby coral is ready to settle, it heads a little bit deeper and looks for nooks and crannies on a reef. It’s looking for a solid substrate. It doesn’t want to be attached to something that’s mobile.” 

There’s also the issue of disembarking. 

“It’s feasible that as this raft of pumice floats towards Australia it goes past some reefs in New Caledonia and picks up a few larvae but there isn’t any mechanism for them to get off the pumice –  which will probably end up blowing up on a beach – and reattaching themselves on the reef,” says Hughes.  

“The only way they could do that would be to stay floating on the pumice for several years until they grow big enough to reproduce and produce another generation of larvae… it’s often three of four years minimum for that to happen.”

And if new coral makes it to Australian shores, it also will be at the mercy of bleaching. This used to happen about every 27 years, but since the 1980s this has increased to every six years. 

About 30% of coral in the Great Barrier Reef died in 2016, followed by another 20% in 2017.

“If we want to improve the condition of the Barrier Reef, we’ve got to deal with the bad things that are happening to it, and those in particular are global warming and run off of pollution from land,” says Hughes. 

This article was originally published on Australia’s Science Channel.

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