Architects and Marine Scientists at University of Hong Kong have developed a new method to protect their reef system in Hong Kong’s eastern shoreline. By using 3-D printed Terracotta tiles specially designed for the attachment of Corals, they found that the chances of survival improved in corals planted in Hoi Ha Wan Marine Park in Hong Kong waters.

These 3-D printed Terracotta tiles or coral houses were deployed in July 2020 in three different locations within Hoi Ha Wan Marine Park. The locations include Coral Beach, Moon Island and a sheltered bay near the WWF Marine Life Center. 

The architectural and marine conservation teams in the project reported that the artificial reef system laid down last summer is now teeming with wildlife including cuttlefish (according to a report). This finding shows a lot of promise and could impact future restoration projects in the area and even globally. 

This restoration project, commissioned by the Hong Kong’s Agriculture, Fisheries and Conservation Department (AFCD) as part of their research into the local coral ecosystem after much of the reefs at According to their report, the Hoi Ha Wan marine park was chosen because of the recently documented events of bioerosion and were struck by bleaching and a mass die-off.

In the past, different projects across the world have deliberately sunk ships or concrete to the seafloor to give corals protected spaces to thrive. This method has been tried out in different locations across the world to varying degrees of success. Even though these methods have had some success in the past they can also change the chemistry of the water. This is where Hong Kong’s method of using 3-D printerd growth mediums reign superior. 

Instead of using concrete, which adds calcium and other minerals to the water and substrate after erosion, they have used Terracotta. This ancient building material made using grog and clay minimises the environmental impact. Clay is basically soil, so it will keep the water chemistry unchanged and if the tile fails to spawn any coral colonies, it will simply erode into the ocean in time without any lasting impact. 

Architects from the Robotic Fabrication Lab, under the Fabrication and Material Technologies Lab of the Faculty of Architecture, and marine scientists from the Swire Institute of Marine Science (SWIMS) of the Faculty of Science at Hong Kong University joined forces to produce reef tile made from Terracotta for corals to attach itself.  After the corals grow, this material will just dissolve away, leaving behind well-rooted coral beds.

How it works

These 3-D Printed tiles are specially designed to aid coral restoration by providing a structurally sound foundation that mimics the natural terrain and crevices that the ocean floor offers. This outer shell also helps mimimse bioerosion, which has been a concern for corals in these waters. These artificial beds are meant to be the anchors for corals that are dislodged and cannot survive on their own. 

Three common species which are common found in the Marine Park – Acropora, Platygyra, and Pavona; were chosen for this study. Tiles seeded with these corals were planted with the idea of creating a diverse habitat for other Marine species. These corals with its diverse growth forms were meant to just do that. 

128 pieces of reef tiles, each measuring 600 mm in diameter were printed with the help of robotic 3-D printers using terracotta clay and blasted with 1125 degree celsius heat to harden. These artificial reef tile design was also inspired from patterns typical to corals (like brain coral and some SPS Coral species) and integrated several performative aspects addressing the deteriorating conditions of Hong Kong waters and helping counter the fluctuating water temperatures, according to the official docket.  

Terracotta Tiles

Corals colonies consist of millions of living polyps, which are invertebrates highly sensitive to temperature changes. When it gets too hot, they lose their vibrant colors and die, failing to attach to a rock surface and grow.  

By using these tiles, the teams also created a controlled environment, allowing for more efficient data collection methods regarding growth patterns, successful attachments, and survival rates. Instead of relying on natural polyps or metallic structures, several other parameters needed to be considered, which these tiles countered effectively.

These tiles are more eco-friendly than the conventional method of using concrete and metal. They are printed using clay and hardened to terracotta in a kiln. Tiles with 400 coral fragments were laid out on a 40 square meter section of the seafloor in the Marine Park.

Results of the Study

The corals that were planted on these tiles now survive better than the traditional way of transplantation. Scientists have estimated the success rate to 90 % which is unprecedented. Since they were planted in the summer of last year, these artificial reefs are now teeming with wildlife, according to the report.

“The first time we put down the tiles, there were a few fish around. Now the artificially produced reef laid down last summer is teeming with wildlife, including the cuttlefish” Vriko Yu was quoted as saying in the report.

In the past, different projects were implemented across the globe using different methods such as sinking ships or the use of concrete and metal to save corals but none have proven to be a success such as this. 

Is There a Future ?

Marine biologists across the globe are all in search of the ideal reef population programs because corals are on the brink of extinction. Global warming and an increase in oceanic temperature have destroyed a lot of coral reef populations, especially the ones in warmer tropical waters. 

Several areas across the world are protected but with little change in their population. Large and popular reef beds like the Australian Great Barrier Reef is now listed by the International Union for Conservation of Nature (IUCN) as “Critical”. This is a major cause for concern because scientists are reporting vast changes in oceanic temperatures, which is proving to be extremely detrimental to coral and other marine fauna health.

Corals that  thrive in subtropical waters are more resilient to climate change and can withstand a greater range of temperature compared to the corals in tropical waters.

Even though 3-D printed Terracotta tiles were a success in Hong Kong they are not a remedy for mass bleaching. But the scientists involved in the Terracotta project hope that they can help identify species with genetic resilience against future environmental stress and buy enough time for the corals to adapt and migrate into more suitable locations.