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From rubble to reef in just four years: How a metal sculpture revived Indonesian coral

DAILY SCIENCE

From rubble to reef in just four years: How a metal sculpture revived Indonesian coral

Interconnected metal stars provide a foundation for an entire new reef to grow on the remains of dynamited coral.
April 3, 2024

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Four decades ago, anglers in the southern reaches of Indonesia’s Sulawesi island used a devastatingly simple tool to catch reef-dwelling fish: they tossed in sticks of dynamite and scooped up the stunned fish that rose to the surface.

The technique had a tremendous downside, however. It turned vibrant coral reefs into fields of rubble. The destruction was so severe that decades later new coral larvae from nearby still couldn’t get a toehold to begin rebuilding the reef.

Despite those setbacks, today parts of the once-devastated reefs are again filling with coral. That’s thanks to the efforts of island residents, Indonesian and British scientists, and a clever metal contraption that resembles a 6-legged spider the size of a coffee table.

The “Reef Stars,” as they are known, have proven so successful that new research shows the fledgling reefs in many ways resemble surrounding healthy reefs.

“The speed of recovery we saw is incredible,” said Ines Lange, a coral reef ecologist from the United Kingdom’s University of Exeter who tracked the reef revival.

Such coral-growing strategies are a mainstay of reef restoration efforts around the world. Small coral fragments—colonies of genetically identical coral polyps living in a shared bony structure—are attached to a frame of some kind and then “planted” out on the reef. In Florida, where the approach was pioneered several decades ago, coral chunks are suspended from plastic frames like ornaments on a Christmas tree until they are big enough to be placed on a reef.

 

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While the metal structures in Indonesia give the tiny corals somewhere to grow, they also provide a foundation for an entire new reef on the remains of the dynamited coral. The metal stars are interconnected into a lattice of steel and coral—a sort of cyborg reef that can cover an area roughly half the size of the penalty box in a soccer field.

To understand how well these new hybrid reefs were faring and how closely they resembled a natural reef, Ines and colleagues took measurements of key indicators from 12 restoration sites, as well as 3 healthy reefs and 3 that were still destroyed.

The results revealed that reefs replanted as little as four years earlier looked a lot like their natural neighbors in important ways. The older restoration sites were creating just as much carbonate exoskeleton as the healthy reefs, and were making three times as much carbonate as in the first year they were planted, the researchers reported in March in Current Biology. The amount of reef area covered by coral rose from 17% to more than 50% as the corals grew back, levels similar to the healthy reefs.

“This is a really encouraging discovery,” said Tim Lamont a marine biologist from Lancaster University, who took part in the research.

The restoration program in Indonesia has been a fount of coral innovation, including the metal stars and using underwater audio recordings to gauge the health of reefs.

 There were, however, subtle differences. The planted reefs were made up almost entirely of fast-growing spiky branching corals favored by reef restorationists. The natural reefs, by contrast, had far more of the bulky boulder-shaped corals mixed in.

That reliance on spiky corals has proven to be an Achilles heel in Florida, where an underwater heatwave last year wiped out huge numbers of transplanted corals from two endangered species.

The Indonesian reefs are less vulnerable, said Lange. There is more genetic diversity among the corals they are using than the ones in Florida. And ocean conditions in the Indonesian waters have proven to be more hospitable to reef-building corals. Lange said that in recent years, corals there remained relatively healthy while many other reefs in the world were bleaching – a phenomenon in which overheated coral polyps risk starving after expelling symbiotic algae from their bodies.

In the long term, however, even these reefs might not escape the ravages of climate change.  A United Nations-sponsored study found that ocean warming means 29 of the world’s most important reef systems (including some near Sulawesi) will vanish by the end of the century without dramatic reductions in greenhouse gas pollution.

Still, Lamont struck a hopeful note about the latest results. “If we can maintain climate conditions that allow for coral survival, it’s possible to restore even very damaged reefs back to healthy, functional systems within relatively short periods of time.”

That’s a very big “if.”

Lange, et. al. “Coral restoration can drive rapid reef carbonate budget recovery.” Current Biology. March 8, 2024.

Image: Mars Assisted Reef Restoration System

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