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November 2022   |   Volume 24 No. 1

Out of the Blue

Making use of robotic 3D printing technology and environmentally-friendly terracotta materials, the project creates suitable habitats for threatened corals using artificial reef tiles to enhance coral survivorship. (Courtesy of Paul Sedille)
Marine ecosystems serve the critical environmental function of sequestering and storing blue carbon from the oceans and atmosphere, an essential tool in the fight against climate change. A multidisciplinary project is developing new ways to protect Hong Kong’s precious marine environment using 3D printing.

First coined more than a decade ago, the term Blue Carbon (BC) describes the disproportionately large stores of carbon in coastal vegetated ecosystems. In the years since, the role of BC in environmental enhancement has reached international prominence, and Hong Kong’s mangrove swamps and seagrass beds are rich stores of it.

However, both of these ecosystems have suffered damage and even destruction over the years, and Dr David M Baker, Associate Professor in the School of Biological Sciences, and his team are working to find ways to protect, repair and nurture the habitats and ensure Hong Kong’s blue carbon stores are preserved.

“We’ve lost so many,” he said. “But if we can restore them we have the potential to mitigate climate change. Coral restoration has piqued interest in the private sector, and even though such ‘animal reefs’ respire just like us, and therefore are a source of carbon dioxide, the tremendous amount of life they support can function to enhance decarbonisation.”

One of the solutions utilises 3D printed structures. “3D printing fascinates me – some are calling it the next Industrial Revolution,” said Dr Baker. “I had never used it before but HKU is a powerhouse for 3D printing in a variety of materials and across a variety of Faculties, including Architecture, Engineering and HKUMed.

“We won a government contract from the Agriculture, Fisheries and Conservation Department to help restore lost coral reefs in Hoi Ha Wan Marine Park, north of Sai Kung Country Park, which is home to more than 60 types of coral and 120 species of fish.”

The reef tile was first adopted by the Agriculture, Fisheries and Conservation Department as an active management tool to aid coral restoration in Hoi Ha Wan Marine Park.
(Courtesy of archiREEF)

Mass mortality

In 2015, an algal bloom of the dinoflagellate Noctiluca scintillans is believed to have caused what Dr Baker terms a mass mortality in the park. “The problem with these algal blooms is that people love them – it’s often called ‘sea sparkle’ because it looks cool – but it is not a good sign for marine life. The reason the cells float is because each one has liquid ammonia in it.”

It was the first time the government had contracted out such a task but, by the time the team was set to start, the site in question had changed dramatically and the reef had eroded away completely, leaving only sand. “Coral won’t grow on sand alone,” said Dr Baker. “We had to come up with a solution, and we decided to tile the seafloor – like you’d tile your bathroom or kitchen. The tiles provided a base for the coral to cling to.”

One diver, one tile

Dr Baker worked on the first design with PhD student Ms Vriko Yu and research assistant Mr Jordan Pierce. “We discussed the design and agreed it should be modular not heavy – one diver should be able to carry one tile – the shape should be hexagonal so the tiles can lock together, and they would be made from terracotta clay and raised off the sand.”

Associate Professor Christian Lange, Head of the Faculty of Architecture’s Robotic Fabrication Lab with Assistant Professor Lidia Ratoi, re-designed the tiles to make them 3D printable in terracotta clay. With their expertise in 3D printing, they also organised and executed the manufacturing of the tiles. In July 2020, 128 reef tiles were placed at three sites in Hoi Ha Wan Marine Park by Dr Baker and his team.

“Those tiles are doing beyond well!” said Dr Baker. “As an active management tool to aid coral restoration they’re really effective. Two years on, the corals are growing so well that the tile is no longer the star of the show – that role goes to the marine life that is covering it. We get mussels, lobsters, female cuttlefish lay eggs in the tiles as they offer great protection.”

The design has since been patented by HKU, and out of this has grown spin-off company archiREEF Ltd – co-founded with Ms Yu, who is also CEO of the company – which has contracts in Hong Kong and overseas, including Abu Dhabi where it has a production facility.

The website sets out the company’s aims: “We offer climate solutions by restoring degraded marine ecosystems. We combine expertise in marine biology and the latest technologies in 3D printing techniques and material science to create artificial habitats that are best suited for threatened marine life.”

Next, the company is working on a Sino Group-funded project in association with the Fullerton Hotel and Ocean Park to create a new reef in Deep Water Bay. “The project includes an outreach plan to invite gifted students to join restoration activities,” said Dr Baker. “There will be opportunities to dive to reefs and full public participation is planned.”

archiREEF is also driving a marine restoration project in Abu Dhabi. “This is a holistic undertaking,” said Dr Baker. “There has been rapid urban development there, and now there is a strong desire to look at nature and how marine life can be maintained and nurtured. It’s all part of the larger picture to work towards climate change resilience.”

3D designed reef tile

A 3D designed reef tile was printed through a robotic 3D clay printing method with generic terracotta clay and then fired at 1,125 degrees Celsius.
(Courtesy of Christian Lange)

Those tiles are doing beyond well! As an active management tool to aid coral restoration they’re really effective. Two years on, the corals are growing so well that the tile is no longer the star of the show – that role goes to the marine life that is covering it. We get mussels, lobsters, female cuttlefish lay eggs in the tiles as they offer great protection.