SINGAPORE — A sheet of pumice, estimated to be the size of 20,000 football fields, is making its way to the Australian coastline and some scientists believe that it has the potential to revive the badly damaged Great Barrier Reef. 

The rise in sea surface temperature due to global warming has driven the degradation of the Great Barrier Reef, the largest coral reef in the world.  

Several back-to-back bleaching events have resulted in a rapid decrease in new coral. In a study published by the journal Nature in April, baby coral in the Great Barrier Reef declined by 89 per cent last year due to mass bleaching in 2016 and 2017.

Bleaching occurs when corals, stressed by factors such as rising water temperatures, expel the algae that live in their tissue and provide them with food. Bleached coral is more susceptible to disease and when there is not enough time to recover, it can die.

WHAT ARE PUMICE RAFTS?

What scientists have dubbed “pumice rafts” were first spotted by Australian couple Michael and Larissa Hoult, who were sailing from the Vava’u islands of Tonga to Fiji in the South Pacific Ocean. Other sailors have also since reported sightings of the raft.

A pumice raft is a mass of floating, porous rock that forms when a volcano erupts from the ocean floor. During a volcanic eruption, the hot magma, frothy and full of gas bubbles, rapidly cools to form pumice. The pumice then floats to the surface due to its gas-rich structure and gathers to form a raft. 

The recent reports of pumice rafting are the result of the eruption of the Home Reef volcano in Tonga in 2006.

HOW ARE PUMICE RAFTS HELPFUL?

Responding on Wednesday (Aug 28) to queries from TODAY, Assistant Professor Huang Danwei of the National University of Singapore’s Department of Biological Sciences, explained how these masses of volcanic rock function as part of the marine ecosystem.

As the pumice rafts pass around “biodiversity-rich habitats” in shallow environments such as coral reefs, corals and other species can latch onto them. The pumice rocks have many crevices where animals and marine organisms can hide and grow, Asst Prof Huang said.

This then allows marine organisms such as algae, barnacles, snails and crabs to travel longer distances and disperse further than they normally would without help from these floating pumice rafts. 

The pumice rafts are also ideal due to their size. Asst Prof Huang added that the large surface area of these rafts can carry more species than other rocks or materials in the ocean. 

Because of these qualities, some scientists have hypothesised that corals can hitch a ride on the raft and eventually break off as they pass over the Great Barrier Reef to form new colonies.

Professor Scott Bryan, a geologist at the Queensland University of Technology, told the New York Times that there is evidence that corals can grow to reproductive size on rocks and may spawn new larvae into the water.

In an email reply to TODAY, Prof Bryan said: “The other main mechanism for colonising is that the pumice becomes heavy and sinks to the seafloor, and the corals and other attached marine life can continue to grow.

So any sunken or trapped pumice on the sea bed can also allow those attached species to then colonise their new environment, in this case the Great Barrier Reef.”

CAN CONDITIONS BE SO TIMELY?

While it is true that pumice rafts do help organisms to move long distances and corals are among the organisms that can attach onto the pumice, it remains to be seen if all these processes can indeed align and work to help revive the Great Barrier Reef.

Asst Prof Huang said that there are a few conditions that have to be met.

First, the corals that have attached onto the raft have to reproduce and spread their eggs and sperms in the water to form larvae.

The larvae has to then settle on the Great Barrier Reef and form a new generation of baby corals to help replenish the depleted reefs

Another scenario is for the coral to break off from the raft and settle onto the Great Barrier Reef and form new colonies this way, he said. 

The process is ostensibly complex, and there is not enough information to ascertain whether the corals will reproduce in time for them to settle on the reef.

He added that it is also unlikely that the corals can break off nicely and conveniently just as they pass over the reef.

WHAT IS UNKNOWN AND WHAT IS KNOWN

There is potential for the pumice rafts to negatively affect the Great Barrier Reef as well. This could happen when the rafts block the light on the reef when it floats over the area. 

In shallow waters, the rafts could also hit the reefs and destroy them, Asst Prof Huang said.

The same qualities of the rafts that aid in transporting organisms can help spread non-native species onto the Great Barrier Reef and some of them could be invasive.

While it is possible that there are corals on the pumice rafts, this has yet to be determined. Scientists are still unaware of what are the specific organisms that are on them, he said.

More research needs to be done before the possibility of the pumice rafts rejuvenating coral reefs can be seriously considered.

“It would be nice if (the pumice rafts can help) but it’s not going to happen in the scale that is going to help the Great Barrier Reef recover,” Asst Prof Huang said, adding that they should not be viewed as a silver-bullet solution.

He stressed that efforts should be focused instead on the “root cause” of the issue, which is climate change.

“We really need to get rid of the root cause of the degradation, which is an increase in carbon dioxide in the atmosphere and (an) increase in sea surface temperatures which is driving the degradation and bleaching. These are the fundamental problems we are seeing.”