How 3D-Printed Artificial Reefs Could Aid Marine Restoration 

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Climate change is driving the destruction of reefs across the world. Sustained spikes in ocean temperatures are causing fatal coral bleaching. Since 2016, half of the Great Barrier Reef has been bleached to death. And in the Northwestern Hawaiian Islands, reefs have experienced their worst bleaching on record.

To mitigate the loss of reef habitats, scientists, engineers, and architects throughout the world are designing and developing 3D-printed artificial reefs.  

In California, architect Alex Schofield hopes to aid the restoration of coral reefs with 3D-printed calcium carbonate structures. Schofield said that following a conversation with a friend about the threats facing reefs and the possibility of 3D-printing coral, he decided to educate himself about the marine environment.

carbonate prototypes being deployed in the San Francisco Bay. Credit: Alex Schofield

This led him to create Coral Carbonate, a project that aims to support the regrowth and propagation of coral and ocean life. He is also collaborating with Architectural Ecologies Lab at California College of the Arts (CCA) – a research initiative bringing together designers, scientists and manufacturers.

Using calcium carbonate – a naturally occurring compound found in limestone, shells, pearls and coral reefs – Schofield is crafting 3D-printed structures that could provide a habitat for coral polyps, tiny marine invertebrates related to sea anemones. Coral polyps secrete calcium carbonate, which subsequently forms into a hard protective skeleton. Reefs develop when a polyp attaches itself to the seafloor and divides into thousands of clones.

However, rising sea temperatures are causing ocean acidification, which is slowing the rate at which coral reefs can generate calcium carbonate.

Schofield said: “Corals are having a really hard time building their skeleton, so one of the goals of 3D printing calcium carbonate is to give coral polyps a leg up.

“Conceptually, you can think of what is being printed as a home for the coral polyps. It’s essentially printing another skeleton, which is a scaffold that the living polyp organism would inhabit and propagate across.”

Although calcium carbonate is a common and easily sourced substance, Schofield said that there is a possibility that carbon could be sequestered from the environment and converted into calcium carbonate.

By observing natural coral skeletons and using 3D-modeling software, Schofield has designed cylindrical structures with maximized surface area to encourage as much marine life as possible.

3D-printed calcium carbonate prototypes Credit: Alex Schofield

Earlier this year, the prototypes were fitted to the base of the Float Lab, CCA’s research platform, which is used to experiment with ways of enriching marine habitats in the San Francisco Bay, where they are currently being monitored.

Schofield said that he is also working with the Coral Restoration Consortium (CRC) to 3D print some of his prototypes to facilitate the growth of staghorn corals, especially in areas where they are having a hard time propagating.

Meanwhile, it’s not just coral reefs that are benefitting from new technological responses. Subtidal temperate rocky reefs covered with kelp, sponges and bryozoa – a type of aquatic invertebrate – that provide a rich habitat for marine life are also facing pressures from overfishing and a changing climate, requiring intervention. 

In Europe, the 3D Printing Artificial Reefs in the Atlantic (3DPARE) project has created reef blocks optimized for the Atlantic waters using 3D printed sustainable, low-impact materials. Funded by Interreg Atlantic Area, which is part of the European Union, the project has brought together marine biologists and engineers from four universities and one research institute in Spain, France, Portugal, and the UK.

Marine biologist and postdoctoral researcher Alice Hall and her colleagues at Bournemouth University in the UK have been providing ecosystem data and assisting with the design and deployment of the reefs. Hall told The Oxygen Project that by connecting natural reef patches, artificial reefs could create refuges for many types of marine species – and provide economic incentives.

“It is very much site-specific, but where we are [Poole Bay in the English Channel], it’s a predominately sandy area, and there aren’t many large-scale natural reefs,” Hall said. “But we do have small patch reefs, so it’s about improving the connectivity of the whole region. If you have small fragmented habitats, [artificial reefs] can provide pathways, so you have connectivity between habitat patches, and that’s really important in terms of improving fisheries.” 

Artificial reef block in Poole Bay surveyed in July 2020 Credit: Alice Hall, Bournemouth University

Hall explained that to make the reef blocks, the team experimented with different materials and designs to identify the structures that would be most attractive to marine life. 

Initially, the researchers tried six different concrete mixes. The 3D-printed samples were then submerged in water and monitored over one, three, six and 12 months as the team tested their structural integrity and colonisation by marine life. 

In the end, they settled on the top two mixes – cement with limestone and cement with recycled glass – and four reef designs. The designs have each been printed using the two formulas, and each design has the same internal features to appeal to a diverse range of species – the reef features include holes, tunnels and overhangs of varying size.

Each university has deployed the reef units, with Bournemouth University submerging theirs in Poole Bay in March. Although Covid-19 restrictions set them back, Hall and her colleagues were finally able to carry out monitoring dives in July, September and October. Hall said that the reef units are doing well, and they are already seeing changes.

“Initially, there was a big influx of red seaweed that covered the whole surface of the reef units,” Hall explained. “With the cooler weather in October, some of that was starting to die back, making space for new species to move in.”

The team saw a variety of life such as crabs, starfish and prawns using the reef units, as well as large shoals of fish swimming around their exterior.

Although the project ends in 2022, Hall and her colleagues are looking for additional funding to monitor the reefs’ long-term effect on the ecosystem and seeking opportunities to upscale the project.

Hall said that the units are relatively easy and cheap to produce, with the most expensive cost being the 3D-printer. The team’s aim is to advise subsequent projects, and one way the units could be used in the future is as the base of offshore wind turbines.  

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