The Reef That Built Itself Back

About 1,000 miles south of Hawaii sits Palmyra Atoll, a ring of tiny islands built by coral on top of a volcano that eroded under the sea long ago. In 2023, a marine heat wave rolled over it and stayed for more than six months. Some of the brightest corals on the reef turned completely white.

Joe Pollock, senior reef strategy lead at The Nature Conservancy, monitors those reefs. He described the bleaching as devastating, the kind of suffering you feel in your own body, and admitted he didn’t know if the reef would ever come back.

Three years later, he returned. Some damage was still visible, and some areas had recovered faster than others. But around the scarred corals were hundreds of small bumps that looked like tiny cauliflowers. Pollock called it a sea of baby corals, and their parents were the survivors of the 2023 bleaching.

If you’ve quietly given up on coral reefs, this story is for you.

Why coral headlines feel so hopeless

The numbers are hard. The Global Coral Reef Monitoring Network reports that living coral worldwide has declined by about 10% since 1980, mostly from repeated bleaching. A strong El Niño is pushing ocean temperatures up again this year, and this round of bleaching could rank among the worst on record.

So it helps to understand what bleaching actually is, because it isn’t automatically a death sentence.

What coral bleaching is

A coral is an animal that shares its body with tiny algae called zooxanthellae, which live inside its tissue like roommates. The algae turn sunlight into food and hand most of it to the coral. That energy builds the skeleton, and the algae supply much of the coral’s color.

When water stays too hot for too long, the partnership breaks down and the coral expels the algae. The tissue turns transparent and you see the white skeleton underneath. That’s bleaching.

A bleached coral is starving. If the water cools in time, algae move back in and the coral can recover. If the heat lasts too long, the coral dies and fast-growing seaweed can take over the space, making it very hard for corals to return.

So what decides which way a reef goes once the heat breaks? Palmyra offers an answer.

Palmyra: a reef with nothing taken away

After the US military built a runway and a few buildings there during World War II, people mostly left Palmyra alone. Today it’s a US National Wildlife Refuge with a small research station and, at most, a few dozen people working there at a time.

Underwater it looks like a city at lunch hour. Schools of fish move among corals the size of cars. A grouper sits at a cleaning station while a tiny cleaner fish picks parasites off its skin. Blacktip reef sharks cruise the edges. Pollock describes corals so tightly packed they grow over one another, which is exactly what a healthy reef looks like and something most reefs lost long ago.

The crew of three

Palmyra’s recovery comes down to three groups doing their jobs.

The cleaners: parrotfish. Parrotfish graze algae off the reef all day. After bleaching, that work becomes life or death, because seaweed grows faster in warm water and moves into any open space. Parrotfish keep that space clear.

The landing pad: crustose coralline algae. This bubblegum-pink crust grows over rock and dead coral, and it’s firmly on coral’s side. Coral larvae drifting in the water often prefer to settle right on top of it. It holds space until conditions are right for corals to move back in.

The bosses: sharks. Palmyra has one of the highest densities of predators ever recorded. Sharks eat mid-sized predatory fish, which eat grazers like parrotfish. With plenty of sharks around, grazers stay abundant. Remove the sharks and the cleaning crew shrinks. That kind of intact food web is rare: oceanic shark and ray populations have dropped 71% since 1970, mostly from overfishing.

There’s a bonus. Research shows corals that survive bleaching often handle heat better and can pass that tolerance to the next generation. The reef growing back at Palmyra may be tougher than the one that bleached. It’s natural selection at work, and some coral species will fare better than others, but the trend points toward resilience.

What about places where people fish?

Palmyra has no towns. So consider Tsitsikamma, a long-protected stretch of rocky coast in South Africa and Africa’s oldest marine protected area.

It’s home to the red roman, a bright red sea bream that tends to spend its whole life in one small patch of reef. Rhodes University researchers fitted red roman inside and outside the protected area with acoustic tags that record movement, a good proxy for activity and health. Then nature ran the test: an intense upwelling followed by a marine cold spell.

Fished populations slowed down as temperatures crashed. The protected population kept moving.

The researchers suggest fishing may remove the bold, active individuals best able to handle temperature extremes. Inside a protected area, those individuals stay in the population and keep breeding. With climate change driving extremes in both directions, networks of protected areas can help build populations ready for what’s coming.

The full picture

Protected areas buy time and resilience. On their own, they can’t save reefs from unlimited warming. The UN’s Intergovernmental Panel on Climate Change projects that at 1.5°C of warming, coral reefs decline by 70 to 90%. Current national pledges put the world on track for roughly 2.6°C by the end of the century.

Tali Vardi of the Coral Restoration Consortium put it plainly to NPR: restoration can’t keep reefs around without changing the trajectory of our climate. Cutting emissions turns down the heat. Protection keeps the survivors in the game so there’s something left to recover. We need both.

The lessons from Palmyra are already spreading. The Super Reefs framework from Woods Hole Oceanographic Institution, Stanford University, and The Nature Conservancy combines water conditions, currents, and coral genetics to find reefs most likely to survive a hotter future, with work underway in places like Maui and Belize. In Florida, Mote Marine Laboratory is releasing hatchery-raised Caribbean king crabs that eat seaweed. In Puerto Rico, teams are bringing back sea urchins for the same job. Different species, same function: rebuilding the cleaning crew Palmyra never lost.

One thing you can do this year

The next time a marine protected area consultation opens in your region, submit one comment of support. These consultations happen more often than people realize and are usually open to anyone. In Canada, Fisheries and Oceans Canada posts them online. In the US, check NOAA or your state agencies. Most countries have something similar.

Your comment can be two sentences. Copy and paste this one:

I support protecting this area because intact ecosystems recover faster from heat waves. Please give science-based protections full weight.

Officials count those comments, and the people opposed to protection always show up.

As Pollock told NPR, Palmyra shows we’re not ready to write the obituary on coral reefs.

Takeaways

• A 2023 marine heat wave bleached Palmyra Atoll for more than six months; three years later the reef is covered in baby corals
• Bleached coral is starving, not dead, and can recover if temperatures drop in time
• Parrotfish, crustose coralline algae, and sharks work together to keep a reef ready to recover
• Corals that survive bleaching often gain heat tolerance and can pass it to offspring
• Protected red roman in Tsitsikamma stayed active through an extreme cold spell that slowed fished populations
• At 1.5°C of warming, coral reefs are projected to decline 70 to 90%, making emissions cuts the primary fix
• A two-sentence comment on your next local MPA consultation makes a measurable difference