Reef Rebirth: How engineering could save the world's coral

An interdisciplinary research team led by MechSE faculty has been tackling this issue for over half a decade. First covered in 2018, the group’s efforts have evolved over the years to encompass an international research team working both in U.S.-based labs and the “field”—in this case, the Caribbean Sea surrounding the island of Curaçao.

Principal Investigator and MechSE Professor Amy Wagoner Johnson leads the ongoing efforts alongside co-PIs former MechSE Assistant Professor Gabriel Juarez and Ivan Racheff Professor Rosa Espinosa-Marzal from the Department of Civil and Environmental Engineering and the Department of Materials Science and Engineering at Illinois. Additional leading researchers on the team include Professor Forest Rohwer from San Diego State University, Associate Researcher Linda Wegley Kelly from the Scripps Institution of Oceanography and coral reef biologist Dr. Kristen Marhaver from the Caribbean Research and Management of Biodiversity (Carmabi) Foundation.

Understanding the Coral Life Cycle

Within the animal kingdom, corals are classified as marine invertebrates that form compact colonies of individual polyps, or cylindrical shaped bodies with a mouth and tentacles that attach at the base to a substrate. In biology, “substrate” refers to any surface upon which a plant, fungus, animal, or other organism lives. Coral typically attach to submerged rocky shoals, often building upon themselves over time to form reefs.

Corals reproduce both asexually, in which a new polyp grows from a parent polyp to expand the colony, and sexually, in which eggs are fertilized by sperm, eventually maturing into larvae called planulae. These microscopic planulae drift in the ocean’s current searching for a suitable surface to settle. Once settled, and having grown into juvenile polyps, they can lay down a calcium carbonate corallite—a cup-like skeleton that adds stability. When adult polyps reach maturity, they recommence the reproductive cycle so that a colony of coral develops over time.

While scientists have made significant progress in sustaining larvae reproduction and growth in a lab setting, transitioning lab-grown larvae to ocean conditions remains challenging. Limited knowledge surrounding the impact of different substrates on coral growth and the larvae’s inability to overcome currents when trying to attach have hindered efforts to regenerate reefs successfully. Thus, we need not only to understand how currents and other reef conditions impact larvae attachment, but also the role that substrates play in both their settlement and growth.

“Coral reefs are among the most diverse ecosystems on Earth, providing habitat and sustenance for a wide range of marine life,” said Espinosa-Marzal. “From an environmental perspective, it’s crucial to preserve these reefs for their immense ecological and global and local economic importance.”

The Research Project

Wagoner Johnson, who was featured on a two-part podcast earlier this year discussing the team’s research, had attended a conference in Jamaica in 2016 with former MechSE faculty member Andrew Alleyne, now Dean of the College of Science and Engineering at the University of Minnesota. The pair’s collaboration had focused on using 3D printing to fabricate bone scaffolds. However, the conference theme was coral.

“We were asked to present our work on printing 3D scaffolds,” Wagoner Johnson recalled. “When I was talking to people [at the conference], I just found coral reproduction really interesting. Based on feedback from the coral biologists, I thought this was a place where we could have an impact—where people who know about materials could contribute to environmental efforts.”

The experience led Wagoner Johnson to pair with Juarez and assemble an interdisciplinary research team focused on coral reef restoration. Wagoner Johnson works to develop new materials to encourage larval attachment at a reef’s surface and Juarez studies larval swimming behavior in ocean-like fluid environments.

“It’s really about keeping an open mind and allowing yourself to imagine big ideas that are outside of your expertise,” Wagoner Johnson said of exploring how her scaffolding research could apply not only to the human body but also to corals. “Illinois is a great environment for moving across fields and using your expertise in different ways.”

Quantifying Coral Growth

Espinosa-Marzal would later bring her materials science and engineering background to the project, helping to frame the group’s understanding of coral growth.

“My group studies biomineralization, the process by which corals grow,” she said. “From a materials science perspective, we can design new, sustainable and environmentally friendly materials that apply the principles of biomineralization.”

As the team experiments with the substrates, Espinosa-Marzal employs advanced microscopic techniques to inspect the coral “skeletal” systems at very high resolution. “We try to connect the skeleton formation and properties with healthy coral growth,” she said. “The coral living [in our tanks now] are healthier than those dying on ocean reefs. We want to translate this into substrate design to support healthier coral in the wild.”

Similar to the impact of temperature on grain formation in metals, slower or faster growth rates influence the microstructure and properties of coral skeletons, which provide structural support and play a critical role in the corals’ survival and function within marine ecosystems. At the microscale, the size and morphology of calcium carbonate crystals, which are secreted through coral polyps, determine the microstructure—including porosity—and ultimately shape the coral’s overall morphology.

Espinosa-Marzal recognizes the opportunities in learning from coral biomineralization. “We aim to develop materials that grow like corals and exhibit self-healing properties,” she explained, highlighting that corals also capture carbon dioxide during growth. “They offer the potential to create a living material that is both durable and capable of changing shape.”

Convergence of Disciplines

Chemist and postdoctoral researcher Joaquin Yus Dominguez joined Wagoner Johnson’s lab at Illinois after earning his PhD in materials science and engineering from Universidad Carlos III de Madrid.

“I was working with ceramic semiconductors,” Yus said of his PhD research. “But the tolls and characterization process for these materials weren’t that different from the approach we take to understand the coral settlement substrates.”

Yus was also already certified as an open water diver, which made him a natural fit for a role on the team. Over the past few years, he has investigated the material properties of substrates for coral restoration and their influence on larval behavior and the skeleton of juvenile coral samples. He has also traveled to Curaçao to join the field researchers diving on the reefs.

“When you introduce biological and ecological factors to the array of material properties, everything changes,” Yus said of the complexity in working with a living material. “There are so many variables that can change the output of the same analysis, even down to minute differences in the coral’s genome.”

Yus has worked with both the substrate material as well as coatings that change the surface properties of the material itself. “We work with hard materials to create the substrate itself—the rock,” he said. “And then we introduce additives to release ions and other chemicals into the surrounding water, and we work with substrate coatings to help attract larvae and promote settlement and attachment.”

During experiments with substrate materials, Yus and others found that calcium carbonate alone did not hold up well when submerged in water long term—instead, the hydrophobic material would break apart over time, prohibiting successful larvae growth. To resolve this, the team added calcium silicate to the mix—a hydrophilic powder that activates when exposed to water. This combination gave the substrate the necessary strength to support growth over time.

Although field researchers located at Carmabi have been collecting gametes (i.e., reproductive cells) and caring for live larvae samples that swim or drift near the reef, due to import restrictions, the research team cannot transport live coral samples to Illinois from Curaçao. However, collaborating researcher Justin Zimmerman, currently the supervisor of the Florida Coral Rescue Center, has been able to send live samples from a reef in the Florida Keys that the team maintains in local tanks. Moreover, larvae that have not latched have a short lifespan—whether in the wild or in captivity—and the Carmabi researchers routinely preserve any dead larvae, shipping them to Illinois for further study.

Fourth-year environmental engineering PhD student Jingyu Li works alongside Yus to experiment with the preserved larvae and juvenile corals. She prepares samples by affixing the larvae in epoxy on top of a manufactured substrate. She then monitors the larvae’s crystalline structure and morphology to understand the substrate’s influence. Although the corals are dead, chemical and mineral substrates can still have a measurable impact.

Li’s personal connection to the project stems from experiences in her native China, where she would see coral reefs while diving in shallow water.

“Coral reefs are very important for maintaining marine life,” Li said. “Due to overfishing and water pollution, the number of living reefs has significantly decreased. It’s important to act.”

Learning What Larvae Like

Alongside Juarez, postdoctoral researcher and physicist Daniel Gysbers (PhD ME 2024) focuses on understanding the hydrodynamics of larval transport.

“I look at how the flow of currents at the ocean floor interact with the topography so that we can create flow structures that assist larvae in attaching to reef surfaces,” Gysbers said. “We perform experiments in a tank where we can generate the same currents as the ocean floor and use lasers to image the particle flow.”

Collaborating researchers in the field at Curaçao send current data for Gysbers to implement. He also had the opportunity to travel to Curaçao to investigate the attractiveness of different substrate chemicals by placing local larvae in a fluid-filled channel and injecting the chemicals at one end. Gysbers observed whether the larvae would swim toward or away from the chemicals and used the data to inform simulations.

Biologist and postdoctoral researcher Jason Baer, who earned his PhD while working in Rohwer’s lab, has also been focused on the ocean floor environment—from a microbial perspective. His doctoral research was on building coral reef arks—positively buoyant structures that could be tethered to the sea floor to provide a friendlier environment for larvae settlement.

“The sea floor environment experiences a lot of change, which makes it a harder place for corals to live,” he said. “We thought that by moving a coral reef community up into the mid-water, or off the sea floor, we might be able to enhance some of those environmental conditions and provide a better environment for corals and other organisms to live.”

These efforts proved fruitful, opening the door to further investigations of ideal materials and methods for floating reef construction. “The corals and other organisms living on these structures were a lot happier than they were on the sea floor,” Baer said.

Back at Illinois, now fifth-year mechanical engineering PhD student Koumudhi Deshpande worked with Gysbers to analyze the swimming patterns from field experiments and build an understanding of how the diffusion of chemical cocktails over a reef can impact larval settlement.

“We had some interesting findings where [the larvae] actually liked some chemicals and were swimming slower and circling more in the presence of them,” she said. “Whereas with other chemicals, they would speed up or swim in a straight line to avoid them. We added these responses to our model to understand the impact on settlement.”

“We found that calcium and strontium ions in certain concentrations can attract larvae, which was interesting because these ions are some of the building blocks for coral exoskeletons,” Gysbers said.

One Undergraduate’s Coral Journey

Mechanical engineering junior Yusuf Jassim had unique insight to contribute to the project—the care and keeping of coral.

“I’d read about the project,” Jassim said of first learning about the coral study prior to coming to Illinois. “I contacted [the research team] because I already had a reef aquarium set up at home.” The process for Jassim to successfully start and maintain a home coral tank had presented its own challenges. “You start with deionized water and mix in sea salt,” he described. “You allow the mixture to sit so that bacteria can grow. Then, you add live rock to introduce new nutrients, and then you can introduce fish and finally coral.”

Jassim’s tank’s capability was a boon to the research team. Yus sent Jassim substrate samples upon which to grow coral fragments so they could investigate the impact of each substrate on growth rate. The samples included natural hydraulic lime (NHL), which hardens in water and consists of calcium silicate and calcium aluminate; 3D-printed biodegradable polylactic acid (PLA) coated with calcium carbonate; and blank PLA as a control. Fragments of coral were adhered to each substrate and monitored for growth rate using imaging.

“Coral are very interesting because they’re actually animals, but they don’t seem like it,” Jassim said of the motivation to keep a home tank. “I think it’s pretty cool to see these fascinating organisms up close.”

With the project and its team expanding, Jassim later helped design the current tank configuration in Newmark Lab, where the Illinois team cares for and continues to monitor coral samples. The system includes multiple main tanks, heating and filtration equipment, and pumps to drive circulation.

Jassim continues to collaborate on the project through an independent study with Espinosa-Marzal. “Coral reefs are declining at an astonishing rate,” he said. “It would be very nice to find materials that can help with larval settlement.”

Hope for the Future of Coral

With the team looking hopefully to the future of coral reef regeneration, their ongoing efforts show no sign of slowing down.

“I think that if we’re going to improve coral restoration outcomes, we have to not only really understand ecosystems at a high level, but also how different environmental conditions like temperature, oxygen level, and alkalinity interact with the geometry of coral reefs,” Baer said. “Corals have a lot of structure and provide habitats for all sorts of biodiversity. [In pursuing restoration], we want to give corals a chance to create that structure.”

“I envision that we will identify substrate compositions that allow coral larvae to settle and grow into mature corals with much more success,” Espinosa-Marzal said. “We need to design substrates that promote higher success in larval recruitment and settlement, are affordable, and support the healthy growth of corals despite ocean acidification and rising temperatures.”

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Funding

The team’s current five-year study, “From Molecules to Sustainable Reef Platforms: Engineering Ecosystems for Coral Recruitment and Survival,” is funded through August 2026 by the National Science Foundation (CMMI 2133675). Their earlier NSF Convergence award was titled “RAISE: Engineering Coral Reef Recovery” (IOS 1848671).

Wagoner Johnson and Espinosa-Marzal were just awarded another three-year NSF grant to further their coral research into the realm of engineered smart, adaptable materials. Inspired by fragmentation -- coral’s ability to heal and regrow after a fragment becomes detached from the main colony -- the team aims to advance the science of biomineralization to design living materials that can grow and heal. (“Biomineralization of coral fragments: Influence of local chemical composition on self-attachment, morphology, growth and microstructure,” (DMR 2453613.)

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Affiliations

Amy Wagoner Johnson is a professor of mechanical science and engineering in The Grainger College of Engineering, a professor of biomedical and translational sciences and clinical sciences in the Carle Illinois College of Medicine, and holds affiliate appointments with the Beckman Institute for Advanced Science and Technology and the Carl R. Woese Institute for Genomic Biology.

Rosa Espinosa-Marzal is the Ivan Racheff Professor of civil and environmental engineering and materials science and engineering in The Grainger College of Engineering, and holds affiliate appointments with the Materials Research Laboratory, Carl R. Woese Institute for Genomic Biology, and the National Center for Supercomputing Applications.