by An underwater experiment to restore coral reefs using a combination of “IVF corals” and recordings of fish sounds could give scientists who fear the fragile ecosystem is on the verge of collapse a “warning of hope” out.
The experiment – a global collaboration between two teams of scientists who independently developed their innovative coral-saving techniques – has the potential to repopulate degraded reef corals, they say.
The first use of the combined techniques, to repair a damaged atoll in the Maldives, will be shown on the BBC One TV series. Our Changing Planetco-presented by naturalist Steve Backshall. Touted as a potential “gamechanger”, it is hoped the technique could be replicated on a large scale to help preserve and revive dying reefs.
“Every coral in every ocean basin in the world is under pressure,” said Professor Peter Harrison, a coral ecologist at Southern Cross University in Australia.
“Many many have died in some reef areas. So we’ll have large spaces of new real estate for coral larvae, but very few coral larvae are being produced because so many adults have died.”
He leads a type of “coral IVF” that involves capturing millions of spawn from “refractory” reproductive coral after it has floated to the surface of the sea or, alternatively, surrounding coral that has withstood a bleaching event with a net cone shape. The net acts like a giant “coral condom”.
“If you’re breeding from refractory corals that can survive heat stress in the lab, the larvae of those corals have higher heat tolerances than other coral larvae,” Harrison said.
The gametes (reproductive cells) then fuse together, fertilize and form coral larvae in floating “nursery” pools, which protect them from predators and prevent them from getting lost at sea. “If we don’t support the process of natural selection by focusing on the survivors, we will lose everything.”
This technique, Harrison said, can produce 100 times more coral colonies than would naturally occur on a reef with the same number of larvae: “And we’re working out ways to get it up to about 1,000 .”
To entice the larvae to settle on a degraded reef, scientists are broadcasting recordings of fish sounds captured near busy, healthy reefs. “We did this and restocked degraded reefs with fish,” said Steve Simpson, professor of marine biology and global change at the University of Bristol.
“Working with Peter was the first time we tried coral. It maximizes the chance that the coral larvae that are being released will find somewhere to live – somewhere that they will then restore the reef habitat.”
Coral larvae, he discovered, can detect sound as the hairs on their bodies move, so they can be “lured” to swim towards and settle on quiet, unhealthy reefs. “It’s like planting a field that will become a forest again,” Simpson said.
In the laboratory, the larvae were particularly attracted to the low-frequency grunts, croaks and rumbling sounds made by territorial fish, which can protect coral growth on the reef. “We’ve found that coral larvae hear their way home as babies, before then choosing where to live for up to 1,000 years,” Simpson said.
“They look very simple, and they don’t have ears or brains, but corals were probably among the earliest animals to tap into their soundscape and dance to the beat.”
Time is running out for coral reefs around the planet. Scientists recently announced that the world is experiencing its fourth planet-wide coral bleaching event since 1998, with 54% of reef areas in the world’s oceans experiencing heat stress high enough to climb on its colorful corals. white Australia’s Great Barrier Reef has experienced its worst bleaching on record, with around 73% of the 1,429-mile (2,300km) reef affected.
Backshall originally came up with the idea of using the soundscape of a busy reef to attract the tiny coral larvae to an extraction area “just bananas”.
“To see that – to bring these gametes into the sea, play healthy reef sounds for them and see them actively start swimming towards them – is probably as close to a eureka moment as I’ll ever get, ” he said.
However, he fears that if global temperatures rise by 2.5C or 3C, “coral reefs are doomed”, regardless of these new techniques: “If we continue with business as usual in terms of anthropogenic climate change, I don’t think that. no matter what we do.
“Tropical reefs are right on the front line. But if we can keep our increased levels of temperature across the planet down to 1.5C, there is a chance – and then these methods will be part of a positive future.”
The world is “very gradually” waking up to the enormity of the global climate emergency, Harrison said. Meanwhile, he and Simpson are “trying to buy time for coral”.
“If we can keep enough reefs alive during the bumpy two or three decades to be able to recover, we have the reefs for the future, when the climate is under control,” Simpson said.
“People say that coral reefs might be the first ecosystem we could lose, and I like to think, therefore, that they are the first ecosystem we can save. If they are predicted, and we can save coral reefs, we can save anything. And they become a beacon of hope.”
