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A team of marine scientists and architects in Hong Kong has created the first 3D-printed terracotta ‘reef tiles’ to help restore eroding local corals. In July, the first clay coral tiles were placed on the seafloor at Hoi Ha Wan Marine Park in Sai Kung as part of a week-long endeavour. Could this be the future of coral restoration and conservation?  

Marine scientists from the Swire Institute of Marine Science (SWIMS) have been collaborating with architects from Hong Kong University (HKU) to construct the world’s first terracotta coral tiles in the hopes of conserving marine habitats. 

Built at HKU’s Faculty of Architecture, the Reformative Coral Habitats Project has been printing clay hexagonal tiles mimicking the natural shape of brain coral since 2016. The 3D-printed tiles placed on the Hong Kong corals limits negative impacts on the ocean’s biodiversity and prevents potential interference with natural coral’s growth patterns. Vriko Yu, a student involved in the project, said the coral tiles act as a ‘substrate that can facilitate coral restoration, while conserving the local biodiversity’.  

The project will see the installation of 128 reef tiles, covering approximately 40 square meters of seafloor in total, at three sites within the marine park. One of the three sites was so badly damaged that its coral communities had deteriorated into sand. 

“Our hope is that our planted corals can become big enough to stabilise themselves and form a natural habitat,” Yu says.

You might also like: Heat-Resistant Corals Found in the Red Sea Bring Hope Amid Climate Crisis

hong kong corals
Photo by Agriculture, Fisheries and Conservation Department via Hong Kong Free Press.

Weighing around 20 kilograms and measuring 65 centimeters in diameter, each tile consists of three parts: the legs, nine-grid layers and six coral-like layers. Together, the tile units act as an anchoring bed for corals to attach to and grow. Lidia Ratoi, assistant lecturer at HKU, says, “the tiles aren’t conventional tiles. Hong Kong’s subtropical climate entails much underwater sedimentation. That’s why our tiles have a lot of perforations so that sediment doesn’t deposit on the surface and suffocate the corals.”

The team hopes that once the environmentally-friendly terracotta tiles have helped to regenerate coral communities, they will erode and disappear into the seafloor. The 3D printed corals have also been carefully designed to withstand the unique water conditions in Hong Kong- marked by water pollution, overfishing, bioerosion and excessive sedimentation- which precipitated the collapse of local marine ecosystems, including corals.

Hong Kong waters are one of the harshest environments for coral to thrive in; those that are able to grow and flourish in such environments are referred to as ‘super-coral’. “Hong Kong is not an easy place for corals … The water quality has improved a lot over the last decade which has given us one important condition to keep the corals healthy. However, there are some external factors like red tides and typhoons which could take away our efforts in a blink of an eye,” Yu told Hong Kong Free Press. 

In addition to restoring marine life and providing habitats for small fish, coral reefs protect coastlines from storms and erosion, provide jobs for local communities, offer opportunities for recreation and are a source of food and new medicines. 

Going Forward

As the project develops, the team will monitor the sites quarterly, collecting data on the amount of corals that attach to the tiles and the biodiversity levels within the developing reefs. Though still in its early stages, the project’s success thus far is a positive advancement towards marine preservation and conservation in Hong Kong. Yu hopes that the project will encourage and inspire other cities to preserve and restore their local reefs: “If we can do it in Hong Kong, we believe other metropolises can do it, too.”

The marine team estimates that the effort will generate a total area of restored coral habitat of about 40 square metres. “This is quite small compared to the total area of coral communities in Hong Kong,” said David Baker, director of SWIMS and associate professor. “However, even small patches of corals can enhance local biodiversity by creating a home for other species, and small patches can be very important in the long-term by generating propagules – baby corals that can settle on nearby areas, thus spreading corals naturally in our area.”

Featured image by: Vriko Yu


Scientists have found that coral reefs in the Gulf of Aqaba at the northern tip of the Red Sea are capable of withstanding temperature increases of up to seven degrees Celsius, providing an opportunity to replicate these heat-resistant corals in other parts of the world to prevent reefs from dying off amid increasing temperatures and consequent bleaching events.

In the study conducted at the University of Eilat, the coral taken from the Gulf was able to withstand temperature increases of up to seven degrees Celsius. In fact, Maoz Fine, who led the research, says that these heat-resistant corals showed improved physiological performance at higher temperatures. 

Despite ocean-surface temperatures in the area warming at the same rate as elsewhere, coral species there have never suffered a documented bleaching event, showing that a large range of corals along the 4 000km Red Sea reef are uniquely resistant to the climate crisis.

Coral reefs around the world are regularly undergoing mass bleaching events as a result of excessively high ocean surface temperatures along with acidification. The Great Barrier Reef, for example, has suffered three mass bleaching events in five years. Half of the world’s coral reefs are thought to have died in the past three decades, and up to 90% of existing coral reefs may die off by 2050.  This new discovery has confounded scientists.

You might also like: How Can The Great Barrier Reef be Saved?

Anders Meibom, a researcher with the Institute of Earth Sciences at the University of Lausanne, says, “This is the only coral reef ecosystem that has a change to withstand the two- to- three degrees of extra heat that we’ll now unavoidably have by the end of the century.”

The implications for coral reefs elsewhere in the world are still being studied. As direct transplants of coral species to other reefs may lead to failure, figuring out how the Red Sea heat-resistant corals survive the extreme conditions then steering the evolution of species could be another possibility. 

Issues arise however, since scientifically assisted evolution takes time and the research into the Red Sea corals is still in its early stages. “We don’t really know what is going on biologically that allows these corals to thrive with temperature disruptions that are killing coral in other places,” says Karine Kleinhaus, a professor of marine science at Stony Brook University in New York. 

The Red Sea feeds into the Indian Ocean through a strait between Djibouti and Yemen. More than 2.5 million years ago, the strait receded, cutting off the Red Sea and rendering it inhospitable. Kleinhaus says that it got ‘hot and super salty, and just about everything died’. When the ice caps melted, the strait reappeared and plant and animal life came back. The coral species that made the journey north through the Red Sea underwent generations of evolutionary selection. “Only those who could withstand the very high salinity and temperatures could move north and colonise,” Kleinhaus says.

Scientists believe that many of the coral species that inhabit the Red Sea today were forged by that migration and can survive- and even flourish- in ocean temperatures hotter than those forecast. 


The Gulf of Aqaba’s coastline is divided among four countries: Egypt, Israel, Jordan and Saudi Arabia.  It will be a challenge to get these four governments- not all of whom recognise each other’s existence- to work together.

The progress of research is further slowed by lack of funds and the travel bans from the coronavirus, as well as the regions’ tense politics. Gathering scientists across regions to form a research expedition has been hindered by Saudi Arabia’s reluctance to allow Israeli scientists in its territorial waters. 

Threats to the reef such as pollution, sewage, and unsustainable development will certainly accumulate, threatening the Red Sea coral reef therefore, countries need to willingly coordinate methods to attract more funding and advocate to protect the ecosystem. 

Olivier Küttel, from the Swiss Federal Institute of Technology in Lausanne, says, “No one country can protect it alone. Egypt can do well, but if Saudi Arabia, Israel or Jordan do poorly, they can very rapidly destroy the whole ecosystem.”

Jordan’s King Abdullah II is among those lobbying to have the reef recognised on UNESCO’s Marine World Heritage List, in the hopes that it will raise the status of the area, make it easier to attract funding for research and pressure governments to protect it.

Featured image by: Daviddarom

Artificial corals provide structural support that could stimulate the recovery of endangered reefs.

The global scale of coral bleaching has tripled since 40 years ago– severe bleaching currently occurs in over 30% of coral reefs globally compared to less than 10% in the 1980s. 

The climate crisis is the leading cause of bleaching events. As the crisis warms the Earth’s oceans, underwater heat waves become more intense and prolonged, placing immense stress on corals. 

When exposed to extended periods of heat, corals begin to expel the plant cells (Zooxanthellae algae) living in their tissues. Healthy corals form a mutualistic partnership with algae, whereby corals provide shelter and nutrients for the algae while the algae produce sugars and lipids that the coral feed on. Sustained heat stress causes algae to release oxygen-free radicals which damages the coral, forcing it to expel the algae and eventually starve to death. 

To date, half of the Great Barrier Reef has been bleached since the massive El Niño heat wave in 2016, with little hope of recovery. The reef could also be about to experience its most widespread outbreak of mass coral bleaching ever, according to the US government’s National Oceanic and Atmospheric Administration. Many coral systems around the world face a similar fate.

Why are artificial reefs important?

To keep up with this widespread bleaching, conservationists engage in a variety of strategies to improve the resilience of coral reefs. The use of artificial structures in particular has proved to be successful in supporting coral growth. 

Coral Nurseries 

Researchers from the Mote Marine Laboratory and Aquarium in Florida set up coral nurseries to restore damaged reefs in 2018.

The researchers first grow corals in artificial ocean-based nurseries. These comprise tree-like structures made from fishing lines attached with plastic branches. The structures hang from a buoy, and individual corals are planted on each branch. 

The corals are incubated to grow to the size of a basketball before they are harvested from the nursery to be planted on the seafloor. Eventually, the newly planted corals will fuse with the larger corals and the reef begins to recover within a year. 

Corals that take a longer time to grow, such as mound and boulder corals, require more effort. These corals are cut into tiny pieces and then planted on round ceramic tiles forming a flower-like structure. The corals grow up to 50 times faster via this process. The ceramic tiles are later implanted into dead corals. 

“It’s a way to jump-start the reef,” says Dr Emily Hall, an ecologist at Mote Marine Laboratory. The laboratory plants thousands of these coral-flowers every year, which typically achieves more than an 80% survival rate.

The team has planted almost 70 000 pieces of corals in the Caribbean Sea in hopes of increasing the coral population to a point where they can reproduce on their own. 

3D-printed Corals  

Artificial corals can also be implanted onto existing coral reefs to bolster their recovery. Researchers from the University of Delaware showed that 3D printed coral models could provide structural support for the restoration of damaged reef systems following a bleaching event. 

The artificial coral structures act as a foundation for coral larvae to settle and grow. They also provide shelter for reef-associated fish and invertebrates, which are crucial for the development of a healthy reef ecosystem, since these fish feed on invasive algae that compete with corals for light and space.  

“Offering 3D-printed habitats is a way to provide reef organisms a structural ‘starter kit’ that can become part of the landscape as fish and coral build their homes around the artificial coral,” says Professor Danielle Dixson, a researcher at the University of Delaware. 

“And since the materials we selected are biodegradable, the artificial coral naturally degrades over time as the live coral overgrows it,” she adds. 

Conservationists in Australia use similar 3D structures to restore coral reefs in the Pacific Ocean. Reef Design Lab, an industrial design studio based in Melbourne, developed a Modular Artificial Reef Structure (MARS) made of ceramic, which can be moulded into complex shapes that fit snugly like Lego blocks within existing coral reefs. 

The MARS system was installed in the Maldives in 2018 as part of the island’s coral farming project. According to Aminath Shauna, spokesperson for the project, “MARS is based on corals that are most widely growing in the Maldives…the 3D-printed reefs have all these contours and shapes that mimic the natural reefs, so that corals can easily attach themselves, which we can’t do by just building regular concrete structures.”

Although artificial corals could offer bleached coral reefs a second chance, it is not a long-term solution to global widespread bleaching. Even under the best conditions, extensively damaged reefs take at least 10 years to recuperate and even then, some reefs never fully recover after a severe bleaching event. 

The key to saving coral reefs is to mitigate the climate crisis through major reductions in global greenhouse gas emissions. Researchers remain optimistic that bleached coral reef systems such as the Great Barrier Reef could recover with conservation efforts coupled with a global drop in carbon emissions.  

This is Part Two of “Improving the Resilience of Coral Reefs.” Read Part One here. 

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