In jade waters off Hong Kong’s east coast, scientists are thrilled to spot a cuttlefish protecting her eggs inside an artificial, 3D-printed clay seabed helping to restore the territory’s fragile coral reefs.
On postcards and in the popular imagination, Hong Kong is a byword for urban density, a thicket of towering skyscrapers crammed along the harbor or clinging to the vertiginous hillsides above.
Yet it is circled by a surprising array of nature and the small number of coral reefs are some of the territory’s best-kept secrets.
Photo: AFP
About 84 species of coral are found in Hong Kong’s waters featuring more diversity than the Caribbean Sea, scientists say.
Most can be found in remote inlets, far from the sediment-filled Pearl River Delta and its busy shipping channels.
However, like all reefs in a rapidly warming world, they are under enormous pressure.
Which is where Vriko Yu, a doctoral student at the University of Hong Kong, and her team of fellow marine scientists come in.
They have begun using 3D-printed tiles that work as an artificial bed for corals to latch onto and thrive, with promising results.
“The first time we put down the tiles, there were a few fish around,” she said during a recent inspection by researchers at the university.
Now the artificial reef laid down in summer last year is teeming with wildlife, including the cuttlefish, something Yu described as “very, very exciting.”
The Hong Kong Environmental Protection Department commissioned research into local coral ecosystems after the reefs at Hoi Ha Wan marine park were struck by bleaching and mass die-offs.
Corals are colonies of billions of polyp invertebrates and are hugely sensitive to temperature changes. When they get too hot, they lose their vibrant color and die.
Repopulating a dead or damaged reef requires suitable ground for the remaining coral larvae to latch onto and build a new home — and the printed tiles have so far proven dependable.
David Baker, an associate professor at the university’s biological science department, said that “3D printing allows us to customise a tile or a solution for any type of environment and I think that’s the real potential that the technology brings.”
Tiles carrying 400 coral fragments have been laid on a 40m2 section of sea floor in the marine park.
“The corals now on the tiles definitely survive better than the traditional way of transplantation,” Yu said, putting the success rate at about 90 percent.
Some projects around the world have deliberately sunk ships or concrete onto the sea floor to encourage coral growth. While those methods have had some success, they can change the chemistry of the water.
The tiles used in the Hong Kong project are made with terracotta, minimizing the environmental impact.
“Clay is basically soil, so soil you can find everywhere on earth,” said Christian Lange, an associate professor at the university’s architecture department.
It leaves water chemistry unchanged, and if a tile fails to spawn a new colony, it will simply erode without leaving a trace, he added.
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