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With coral reefs in crisis due to climate change, scientists have engineered a bio-ink that could help promote coral larvae settlement and restore these underwater ecosystems before it's too late. In a paper published in Trends in Biotechnology, researchers demonstrate that the ink could boost coral settlement by more than 20 times, which they hope could contribute to rebuilding coral reefs around the world.

"When people think about a coral reef, they often think about how beautiful it is," says author Daniel Wangpraseurt of the University of California San Diego. "What we sometimes forget is that coral reefs are one of the best structures for protecting our coasts. We are hoping to develop technologies to restore not just the ecosystem but the natural structures that will buffer shorelines against waves, storms, and floods."

In the past, researchers have tried to restore coral reefs鈥攚hich have halved across the globe since the mid-20th century鈥攎ainly through planting nursery-grown corals. But Wangpraseurt says these lab-grown corals are genetically identical, meaning that they're susceptible to the same threats.

"If there's a warming event or a disease outbreak, it can wipe out the whole population. Ideally, we want to recruit corals naturally, which can introduce genetic diversity to the population and enhance their resilience," says Wangpraseurt.

Biologists have recently discovered that certain rocky pink algae, called crustose coralline algae (CCA), play an important role in attracting coral larvae and encouraging them to settle on the reef. It appears that CCA emits metabolites into the surrounding water, and coral larvae follow these chemical signals.

Inspired by this finding, Wangpraseurt and his team, including first author Samapti Kundu at the University of California San Diego, developed a transparent ink material infused with metabolites derived from CCA. Dubbed SNAP-X, the ink slowly releases these natural chemical cues into seawater over the course of a month. By applying SNAP-X to rocks or other surfaces, researchers can create an inviting microhabitat that helps coral larvae settle and grow.

The team tested SNAP-X outdoors using natural seawater and continuous water flow to simulate the ocean environment. They found that the larvae of Montipora capitata, a primary reef-building coral in Hawaii, were 20 times more likely to settle on substrates sprayed with SNAP-X, and the settlements became denser when the team increased the concentration of the metabolites in SNAP-X.

Given that some species of coral reproduce by releasing their eggs and sperm at the exact same time every year, the researchers recommend syncing SNAP-X deployment with the coral's spawning cycle to support natural coral recruitment. Depending on the species of coral, scientists can also tweak the ingredients of SNAP-X to include different metabolites and chemical signals that support the development of coral reefs.

The team is now working on methods to scale up the production of SNAP-X. Because the ink contains no living materials, they hope that it will soon be approved for application in the real world.

"It's really exciting to be able to learn from adjacent disciplines like materials science and bioengineering," says Wangpraseurt. "I think a lot of the technologies for restoring and protecting our environment are already there, we just need to look outside the box into other fields of study."