Scientists are reporting encouragingly rapid coral growth on giant underwater steel cages – structures that they hope will help to regenerate battered reefs and improve protection of some vulnerable coastlines from rising sea levels.
Coral reefs support a quarter of life on Earth and last month David Attenborough warned that carbon dioxide is already above the levels that will condemn corals to extinction.
And while the metal cages, fed with electric current, are not a solution to the global problem of dramatically contracting reefs, they do appear to be providing promising results in small, local projects, and – in some cases – rescuing resorts where coral was vanishing fast.
A team of researchers on Vabbinfaru island in the Maldives submerged a huge steel cage called the Lotus on the sea floor. The 12-metre structure, which weighs 2 tonnes is connected to long cable which supplies a low-level electric current. The electricity triggers a chemical reaction, which leads to calcium carbonate coming out of solution in the water and being deposited on the structure.
Corals seem to find that irresistible, perhaps because they use the same material to grow their protective skeletons, and the Lotus has been so thoroughly colonised by coral that it is difficult now to make out the steel shape beneath all the elaborate shapes and colour.
The idea was initially developed by an American architect, Wolf Hilbertz, who sold the concept to various resorts around the world. The Lotus is the largest and most successful of those, and has helped researchers to test the technique.
The El Nino Pacific-warming phenomenon of 1998 killed 98% of the reef around Vabbinfaru, so the researchers there have been able to compare the growth rates for corals grafted on to concrete structures on “desert” patches of seafloor, and those stuck on to the Lotus. Abdul Azeez, who is leading the Vabbinfaru project, said coral growth on the structure is up to five times as fast as that elsewhere.
The electric reef may also make the corals fitter and better able to withstand warming events, perhaps because the creatures waste less energy on making their skeletons. A smaller prototype device was in place during the 1998 warming event and more than 80% of its corals survived, compared to just 2% elsewhere on the reef.
Hilbertz, who died in 2007, believed that his structures could be multiplied across the world to repopulate reefs and protect shorelines. But many experts think the cost and effort involved make it impossible to do except on a small scale.
“I would like to be able to carry out genetic analysis of the algae in the coral to find out whether we can transplant heat-tolerant ones to parts of the reef where it is more exposed and so build coverage there,” says Robert Tomasetti, a marine biologist also based at Banyan Tree resort in Vabbinfaru. “We don’t have that level of equipment so we’re really just growing pretty reefs for the tourists but not in a construction way to protect the island.”
While welcoming the positive impact that the project has had on Vabbinfaru, Shiham Adam, the director general of the Maldivian government’s Marine Research Centre in Male warned that the wider picture for his country remained bleak. “Sprucing up small bits of reef can add value to a tourist resort but it certainly won’t help protect the Maldives from sea level rise,” he said.