The oceans are getting hotter and coral reefs are burning up. These undersea cities, built over centuries by tiny animals called corals, are unraveling in mere decades.

Corals are not solitary architects — they are symbiotic collectives, reliant on microscopic algae that live inside their tissues and provide them with both color and energy. But when the waters grow too hot, this partnership breaks down. The algae flee, the corals bleach, and what follows is not just a loss of color, but a loss of life. The very scaffolding of coral reef ecosystems unravels.

Corals can’t flee the heat. They are anchored in place, passive victims of a changing climate. But scientists can help — not by rescuing individual corals, but by giving new ones a fighting chance.

In a new study, a team of researchers has unveiled a bioengineered ink — an artificial chemical signal that mimics the scent trails of healthy reefs. It draws baby corals, still floating and searching, like moths to a flame. In early tests, this ink boosted settlement rates more than twentyfold, offering a tantalizing glimpse of how science might coax reefs back to life, molecule by molecule, larva by larva.

Corals need nelp

Let’s not sugarcoat it: coral reefs are in deep trouble. Climate change, pollution, and overfishing have already wiped out half the world’s reefs since the 1950s. By 2050, scientists estimate that 70 to 90% of coral reefs could vanish entirely.

For the oceans, this is devastating. Coral reefs are the “rainforests” of the ocean — ecosystem hotspots, home to a quarter of all marine species. They buffer coastlines against waves and hurricanes, support global fisheries, and pump billions into economies through tourism and aquaculture. And yet, they are vanishing faster than forests or glaciers.

“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 in 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.”

No matter what we do, a lot of corals will disappear. But we can still save some of them and mitigate our damage. To do this, we’ll need to help rebuild the reefs. The most efficient approach is to get coral larvae to repopulate bleached reefs rather than building new ones.

A bait for corals

Much of the current reef restoration effort focuses on transplanting coral fragments grown in nurseries. It’s noble work (and often necessary) but there’s a catch. These cloned corals lack genetic diversity. They’re like a field of identical wheat: one damaging pest and everything goes down.

“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.

But how do you convince the coral larvae to come in?

Coral larvae aren’t mindless drifters. As they swim through the sea, they sniff out cues in the water. In particular, signals from crustose coralline algae (CCA), the rocky pink seaweed that crusts over healthy reefs. These algae release chemical compounds that whisper to coral larvae: settle here, grow here, this place is safe.

But on degraded reefs, that message is missing. Turf algae and slime mold often taken over. The chemical landscape becomes hostile, and coral larvae keep swimming until they die.

Enter SNAP-X. It’s part materials science, part bio-mimicry. Wangpraseurt and his team, including first author Samapti Kundu, harvested the very metabolites from CCA that induce coral settlement. Then they embedded these molecules into silica nanoparticles suspended in a hydrogel. The result is a transparent, sticky coating that slowly leaks these chemical cues into the water for over a month.

Spray it onto a rock, and it’s like putting up a neon sign for coral larvae saying “Safe neighborhood! Great schools!”

Promising tests

In outdoor trials using natural seawater and continuous flow — conditions that mimic the open ocean — the researchers tested SNAP-X on Montipora capitata, a key reef-builder in Hawaii. The results were excellent.

Larvae were more than 20 times more likely to settle on surfaces treated with SNAP-X compared to untreated controls. Not only did they settle, but they clustered — denser, more vibrant, more promising colonies. And when the team increased the concentration of the metabolites in the ink, the settlement rates climbed even higher.

What’s more, the ink is adaptable. Different coral species respond to different cues, so SNAP-X can be tweaked like a recipe, swapping in different metabolites depending on the coral community you’re targeting. Here’s where it gets even wilder. SNAP-X is photopolymerizable — meaning you can harden it with light. That opens the door to light-assisted 3D printing of reefs. Think of it as crafting tiny coral condos, precisely shaped and chemically tuned to match natural reef structures.

The ink has reached what engineers call Technology Readiness Level 4 — meaning it works well in controlled outdoor environments but hasn’t yet been deployed in the open ocean. The next step is scaling up.

There is, however, one burning question: how does SNAP-X impact the long-term health and growth of the settled corals? If this is a coral nursery, does it raise strong juveniles? Or do they grow up fragile?

For now, the early signs are good. This won’t save corals all on its own, but it can be an important tool in our race to save the corals. Because make no mistake: the race is on.