(CNN) — With a reputation as a concrete jungle, few know that Hong Kong is one of Asia's most biodiverse cities and boasts more hard coral species than the Caribbean.
But these corals are under threat from pollution and rapid urban development.
ArchiREEF, a spin-out company from Hong Kong University, says it has a solution: 3D-printed terracotta tiles designed to help corals grow and restore ocean life.
Co-founded in 2020 by marine biology professor David Baker and PhD student Vriko Yu, the company hopes it can help make corals "more resilient" against climate change.
Found in warm, shallow water, coral reefs cover less than 1% of the ocean floor but host 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 coral at Hoi Ha Wan Marine Park since 2016 in partnership with the Agriculture, Fisheries and Conservation Department (AFCD).
Hoi Ha Wan, now a protected coastal reserve, in the north of Hong Kong, used to be the site of coral mining for construction materials. This created a major barrier to restoration, says Baker as "the hard bottom of the seafloor has been mined away," leaving only sand and rubble.
The team needed to create a new "bottom" for the corals to grow on. Working with the university's architecture department, they began developing an artificial coral reef using the university's 3D printing facility.
This artificial reef is made from tiles that are roughly two feet wide, and mimic the natural shape of platygyra, known as "brain coral." Its twisting "valleys" attract marine life which can nest or hide from predators, says Yu.
A cuttlefish living in ArchiREEF's clay reef tile test site in Hoi Ha Wan Marine Park, Hong Kong.
Once placed in the water, the team attach baby corals to the tile with non-toxic glue. The shape of the tile helps the corals grow upwards, attracting marine life that build their homes in the reefs.
More than 130 of these tiles were installed on the seabed in Hoi Ha Wan Marine Park in the summer of 2020, and archiREEF was born.
The 3D-printed tiles are just one small part of archiREEF's business model. After engaging corporate clients and governments to sponsor a restoration project, archiREEF will identify a site for restoration, install the reef tiles, and continue to manage the site for up to five years, monitoring the growth and the biodiversity of the reef.
Conventional artificial reefs, such as submerged concrete structures, often replace the function of the coral as a habitat for marine life, says Yu, whereas archiREEF wants to provide a "foundation" for the coral to grow on. Eventually, the coral will be strong enough to support itself without the tile -- which can then be shattered by divers, or will naturally erode.
Baker says that archiREEF can help regrow coral in areas where it has entirely disappeared, a situation which is becoming more common: scientists predict that warming ocean temperatures and increasingly acidic waters may destroy up to 90% of coral reefs globally in the next 20 years.
A diver positioning a 3D-printed terracotta tile on the sea floor.
An 'innovative' approach
Companies such as Australia-based Reef Design Lab and D-Shape have previously 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 similar chemical makeup to real reefs. The 3D printing technology also offers unlimited customization, which the architects at Hong Kong University say enabled them to create more places for the corals to grow and combat specific environmental problems with a bespoke design.
However, Chui also adds that people need to be "realistic" about restoration and consider the cost and accessibility of technology. Places like Hong Kong also need more data on the efficacy of conservation efforts before it can be scaled in a meaningful way, she says, adding: "Restoration should be the last resort; we should protect before we restore."
Conservation for everyone
Rescuing these reefs can help sustain the planet's underwater ecosystems, such as seagrass meadows, which benefit from coral reefs, and are important carbon stores.
There are economic benefits to coral reefs, too. According to a 2021 report from the Global Fund for Coral Reefs, coral reefs support the lives of around one billion people through coastal industries such as tourism and commercial fisheries, as well as providing coastal defense from storms.
Fossil evidence points to corals living in Hong Kong for thousands of years.
ArchiREEF still has a way to go before scaling up. The team will observe the test site in Hoi Ha Wan for at least another two years to ensure the corals continue to thrive and survive natural disasters, such as typhoons. However, Yu says the results at the test site so far are promising: in the first six months of observations, four times more coral has survived on the clay tiles compared to conventional artificial reefs.
A further 10 test sites are already planned, which the startup will use to refine the 3D-printing process and explore alternative materials, as producing clay is energy intensive and produces large amounts of carbon dioxide.
While archiREEF's focus is currently on government and large corporate clients, it hopes to one day engage individuals in its projects, too.
"Restoration is currently restricted to conservation scientists," Yu says. "But if we're talking about stakeholders, it's everybody."