Inside a quest to learn about the ocean’s mysterious “deep reefs”

An autonomous reef monitoring structure (ARMS) in the mesophotic zone. | © Luiz Rocha PALAU, Micronesia — On a bright, sunny day last May, I stood on a boat surrounded by the turquoise waters of the island nation of Palau.

I was there in the western Pacific watching scuba divers as they prepared to bring up evidence of a mysterious aquatic world.

Palau is famous for its spectacular and rich coral reefs.

But these divers were planning to descend past those sun-lit marine communities and down into a lesser-known twilight zone known as the “mesophotic coral ecosystems.” Mesophotic essentially means “middle” and “light,” which is where these ecosystems are — not quite in the bright daylight, not quite in the profound darkness, but somewhere in between.

For simplicity’s sake, we’ll call these communities, which range from some 30 meters to 150 meters below the surface, the “deep reefs.” One of the divers on the boat with me was a zoologist and curator at the California Academy of Sciences named Luiz Rocha, who has spent decades studying these deep reefs and their secrets.

“Anything between 30 meters and 150 meters is really, really unknown,” he told me.

Because these deep reefs are so unknown, researchers like Rocha are left with big questions.

They want to get a baseline picture of what is going on in these ecosystems — even just who lives there! — so that they can better understand how they function.

They’ve also tried to work out whether ( or not ) these deep reefs might provide a refuge for species living in shallower coral reefs.

I was in Palau for Vox’s Unexplainable podcast because, in an effort to gather more information about these mysterious places, Rocha left some scientific structures down in these twilight depths back in 2016.

Those structures then spent almost a decade becoming encrusted with all kinds of marine life.

And now, Rocha was back to retrieve them, hoping that he — along with many other scientists — would be able to open them up, like a box of scientific puzzle pieces, full of clues about this under-understood marine world.

View Link So what is a mesophotic “deep reef”? One thing that’s often acknowledged in papers about and descriptions of the “mesophotic coral ecosystems” is that scientists don’t know as much as they’d like to.

A National Oceanic and Atmospheric Administration article about them from 2019 is full of “may’s” as in: they may “serve as essential fish habitat for economically and ecologically important species.” Researchers do know some things, of course.