Water works: Divers planting coral fragments on an artificial reef tile whose grooves mimic the Platygyra coral in Hong Kong. — Bloomberg
HONG KONG: In the subtropical sea off northeast Hong Kong, orange and white-striped clownfish somersault like acrobats, black sea urchins furtively wiggle their antennas and crabs shuttle between crevices in a leggy panic.
Much of this activity in Hoi Ha Wan Marine Park gravitates around corals that are thriving on an artificial reef made of 3D-printed terracotta tiles, installed two years ago by researchers at the University of Hong Kong (HKU).
“The corals have grown so much since I last dived here,” said Vriko Yu on a recent afternoon, moments after resurfacing in the protected, jade-colored waters.
“What excites me is the way you can see the species are quickly making a home here.”
The reef tiles are thought to be the first use of clay for 3D printing in the world. They were produced by Archireef, a company spun off from the university and co-founded by Yu, a former PhD student, and marine biology professor David Baker. The company will present its work at the upcoming COP27 climate summit.
Its terracotta hexagons could be a building block in efforts to protect and restore vulnerable coral reefs, which cover less than one percent of the ocean floor but host more than 25% of all marine life.
They might also help to cultivate corals that are more resilient to waters warming rapidly because of climate change.
Hong Kong’s Agriculture, Fisheries and Conservation Department launched efforts to restore the reefs at Hoi Ha Wan after toxic “red tide” algae blooms in 2015 and 2016 killed off 90% of its Platygyra, one of the major local coral species.
Initially, in late 2016, scientists attempted to revive the reefs by gluing living coral fragments directly onto rocks. But the corals grew very slowly, often detaching and dying. In response, researchers developed the 3D-printed tiles.
In 2020, divers placed 400 coral fragments, which had been naturally dislodged in the ocean, into the ridges of the tiles, which measure 50cm2 and weigh around 15kg each.
Designed to mimic the complex shape of Platygyra, or “brain coral”, the tiles contain crevices and niches for coral seedlings and marine life to settle in while also minimising build-up of the sediment prevalent in Hong Kong’s waters.
The bottom half of the tile is designed like a snowshoe, providing stability on sandy seabeds, which have become common due to Hong Kong’s high rates of bioerosion.
“Corals aren’t like trees, they don’t have roots,” says Yu. “They can’t attach to sand. They must be connected to substrate. So, we had to kind of renovate the sea floor.”
Concrete, which is often used in coral restoration projects, can affect the chemical balance of coral ecosystems. But clay is slightly acidic like the calcium carbonate found in real coral reefs and will, in theory, erode over decades, leaving behind healthy coral.
The 3D-printing process is cheaper than pouring concrete and allows for customisation, with bespoke designs combating specific environmental problems posed by a location.
Hong Kong is home to over 100 coral species, more than the Caribbean. — Bloomberg
