By Donna Ferguson, The Guardian
Recordings of healthy fish are being transmitted to attract heat-tolerant larvae back to degraded reefs in the Maldives.
An underwater experiment to restore coral reefs using a combination of “coral IVF” and recordings of fish noises could offer a “beacon of hope” to scientists who fear the fragile ecosystem is on the brink of collapse.
The experiment – a global collaboration between two teams of scientists who developed their innovative coral-saving techniques independently – has the potential to significantly increase the likelihood that coral will repopulate degraded reefs, they claim.
The first use of the combined techniques, to repair damaged atolls in the Maldives, will be shown on the BBC One TV series Our Changing Planet, co-presented by the naturalist Steve Backshall.Hailed as a potential “gamechanger”, the hope is that the technique could be replicated on a large scale to help preserve and revitalise dying reefs.
“All corals in all ocean basins in the world are under pressure,” said Prof Peter Harrison, a coral ecologist at Southern Cross University in Australia.
“Quite a large number have died in some reef areas. So we’re going to end up with big spaces of new real estate for coral larvae, but very few coral larvae being produced because so many adults have died.”
He has pioneered a form of “coral IVF” that involves capturing millions of spawn from “heat-tolerant” reproductive coral after it floats to the sea surface or, alternatively, surrounding coral that has withstood a bleaching event with a cone-shaped net. The net functions like a huge “coral condom”.
“If you breed from heat-tolerant corals that can survive heat stress in the laboratory, the larvae of those corals also have higher heat tolerance than the larvae of other corals,” said Harrison.
The gametes (reproductive cells) then merge together, fertilise 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’re going to lose everything.”
This technique, Harrison added, 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 to about 1,000.”
To attract the larvae to settle on a degraded reef, the scientists are broadcasting recordings of fish noises that were captured near a busy, healthy reef. “We’ve done 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 is the first time we’ve tried it with corals. It maximises the chance that the coral larvae being released find somewhere to live – somewhere that they will then restore the reef habitat.”
Coral larvae, he has discovered, can detect sound according to the way the hairs on their bodies move, and so can be “tricked” into swimming towards – and settling on – a typically silent, unhealthy reef. “It’s like sowing a field that will become a forest again,” said Simpson.
In the lab, the larvae were particularly attracted to the low-frequency grunts, croaks and rumbling sounds made by territorial fish, which can protect coral growing on the reef. “We have discovered that coral larvae hear their way home as babies, before they then choose where to live for up to 1,000 years,” Simpson said.