Reputed to be a concrete jungle, few know that Hong Kong is one of the most biodiverse cities in Asia and has more species of hard corals than the Caribbean.
But these corals are threatened by pollution and rapid urban development.
ArchiREEF, a spin-out company from the University of Hong Kong, says it has a solution: 3D-printed clay tiles designed to help corals grow and restore life in the ocean.
Co-founded in 2020 by marine biology professor David Baker and doctoral student Vriko Yu, the company hopes to help make corals “more resilient” to climate change.
Found in warm, shallow waters, coral reefs cover less than 1% of the ocean floor but are home to more than 25% of marine life. Corals, invertebrate animals that live in vast underwater colonies that form reefs, have existed in Hong Kong for thousands of years, but pollution and coral mining have decimated the population.
Baker and Yu have been trying to restore corals in the Hoi Ha Wan Marine Park since 2016 in partnership with the Department of Agriculture, Fisheries and Conservation (AFCD).
Hoi Ha Wan, now a protected coastal reserve in northern Hong Kong, used to be the mining site of coral for building materials.
This created a major barrier to restoration, says Baker, as “the hard seabed was mined away,” leaving only sand and rubble.
The team needed to create a new “bottom” for the corals to grow. Working with the university’s architecture department, they began to develop an artificial coral reef using the university’s 3D printing facilities.
This artificial reef is made of tiles about 60 centimeters wide and mimics the natural shape of the platigira, known as “brain coral”. Its tortuous “valleys” attract marine life that can nest or hide from predators, says Yu.
Once placed in the water, the team fixes the baby corals to the tile with non-toxic glue. The shape of the tile helps corals to grow upward, attracting marine life that build their homes on the reefs.
More than 130 of these boards were installed under the sea in Hoi Ha Wan Marine Park in the summer of 2020, and archiREEF was born.
3D printed tiles are just a small part of archiREEF’s business model. After engaging corporate clients and governments to sponsor a restoration project, archiREEF will identify a restoration site, install the reef plates and continue to manage the site for up to five years, monitoring the reef’s growth and biodiversity.
Conventional man-made reefs, such as submerged concrete structures, often replace the coral’s function as a habitat for marine life, says Yu, while archiREEF wants to provide a “foundation” for coral to grow.
Eventually, the coral will be strong enough to support itself without the tile – which can be broken by divers or undergo natural erosion.
Baker says archiREEF can help regenerate corals in areas where they have completely disappeared, a situation that is becoming more common: scientists predict that warming ocean temperatures and increasingly acidic waters could destroy up to 90% of coral reefs of the world in the next 20 years.
An ‘innovative’ approach
Companies like Australia’s Reef Design Lab and D-Shape have already used 3D printing to create underwater habitats. But archiREEF’s use of clay, a non-toxic and natural material, is “innovative,” says Pui Yi Apple Chui, a coral restoration researcher at the Chinese University of Hong Kong.
Unlike concrete, clay is slightly acidic, like coral, and has a chemical composition similar to real reefs.
3D printing technology also offers unlimited customization, which has allowed architects at the University of Hong Kong to create more places for corals and tackle specific environmental issues with design.
However, Chui also adds that people need to be “realistic” about restoration and consider the cost and affordability of the technology.
Places like Hong Kong also need more data on the effectiveness of conservation efforts before they can scale significantly, he says, adding: “Restoration should be the last resort; we must protect before restoring.”
conservation for all
Restoring these reefs can help sustain the planet’s underwater ecosystems such as seagrass meadows, which benefit from coral reefs and are important carbon sinks.
There are also economic benefits to coral reefs. According to a 2021 report by the Global Fund for Coral Reefs, they support the lives of an estimated one billion people through coastal industries such as tourism and commercial fishing, as well as providing coastal defense against storms.
ArchiREEF still has a long way to go before it scales up. The team will observe the test site in Hoi Ha Wan for at least two more years to ensure the corals continue to thrive and survive natural disasters such as typhoons.
However, Yu stresses that the results at the test site so far are promising: in the first six months of observations, four times as many corals survived in the clay tiles compared to conventional artificial reefs.
Another 10 test sites are already planned and should be used to assess the refinement of the 3D printing process and explore alternative materials as clay production consumes a lot of energy and produces large amounts of carbon dioxide.
While archiREEF’s focus is currently on government and large corporate clients, it hopes to one day involve individuals in its projects as well.
“Restoration is currently restricted to conservation scientists,” said Yu. “But if we’re talking about interested parties, it’s everybody.”