I read some incredibly heartening news today! Enric Sala with National Geographic published an article (paywalled, but NPR also covered it in less detail) about the remarkable recovery of previously devastated corals around the southern Line Islands. In 2015 and 2016, the strongest El Niño ever recorded passed through the area, and half the corals died. When Sala's team was able to check back in 2021, dreading what they would find, they were surprised to see that much of the reef had come back to life.

Sala writes:

What did we learn from the recovery of these “super reefs”? The corals that were resistant to the phenomenal 2015-16 El Niño provided the reefs’ resilience. The southern Line Islands lie in one of the hottest hot spots of warming in the Pacific Ocean, so the corals here apparently have adapted to heat.

For new corals to grow over dead ones, though, the skeletons need to be covered by pink encrusting corallines instead of fleshy seaweed. What provided these ideal conditions in the southern Line Islands? We believe one reason is the off-the-charts abundance of herbivorous fish—the enormous parrotfish and schools of hundreds of surgeonfish. They’re grazers, the zebras and antelope of the reef, and they gobble every tiny fleshy alga that dares to grow on the dead coral. When you’re diving in the shallows, you hear those fish scraping at the reef nonstop. Crustose coralline algae, which have calcareous skeletons, survive the grazing. The fish prefer to eat the equivalent of yummy lettuce rather than limestone.

That observation reinforces the conclusion we reached in 2009: Full protection from fishing, and the enormous fish biomass it yields, is necessary for a reef to be able to bounce back. Full protection promotes resilience. But will it be sufficient if extraordinary warming events like the 2015-16 El Niño become more frequent? Will these reefs have enough time to recover in between crises? We don’t know.

There are also caveats. Though the coral in aggregate recovered, specific species might not:

The reefs were back with exuberance, but they were changed. Here and there, Pocillopora that had died in 2015-16 were recovering slowly, sometimes on top of their dead, like trees sprouting from stumps in a coppiced forest. But most of the space left by the dead corals had been filled by other species.

And the giant clams, which are amazing ocean filters, were still devastated:

In 2009 we had counted more than 29 giant clams per square yard in those areas; in 2021 three hours of swimming over the lagoon reefs revealed only five living clams. The seawater temperature in 2015-16 probably had been much higher in the lagoon than in the fore reef around the atoll. That created a lethal clam bake, from which the giant clams may never recover.

It also seems like the explanation given for the recovery is still only a hypothesis.

Nevertheless, the complexity of ecology is always surprising us. It brings to mind our attempts at mapping the human brain. There are so many connections we cannot yet see, just as artificial neural networks are still nowhere near the simple, flexible intelligence we take for granted in organic beings. In both cases, we still don't really understand what it is that makes the world come to life.

As such, it is another reminder that nature often does a much better job at restoring itself than any human interventions can. Which makes it even more important to preserve as much biodiversity as we can everywhere. We don't know how everything works, but we know there is wisdom in our ecosystem.

It reminds me of a quote I heard once by Leo Szilard that has always stuck with me. Szilard was a physicist that patented the idea of a nuclear fission reactor in 1933 and worked on the Manhattan Project to develop an atomic bomb as a deterrent against Nazi Germany. But he also fought publicly and in vain to stop the atomic bomb from being used. He wrote simply:

Do not destroy what you cannot create.

And that includes of course the coral, the fish, the clams.