A Decade-Long Experiment Is Unlocking the Mysteries of the Ocean’s ‘Deep Reefs’

Researchers do know some things, of course. They know that these deep reefs can be found in many of the same regions as shallower coral reefs—so mainly the tropical and subtropical parts of the world, like Micronesia, the Caribbean, and even the Gulf of Mexico. They’ve found that there are many species that seem to be unique to these places, and recent research points to their potential susceptibility to climate change.

Researchers have also gotten a sense of some of the key differences between these deep reefs and their shallower coral neighbors. In shallow reefs, hard corals team up with photosynthesizing algae. The algae provide the corals with nutrients, and the corals secrete a calcium-carbonate matrix that helps create the architecture of the reef.

As you go deeper, though, the light begins to fade, and the opportunities for photosynthesis start to fade with it. The temperature also drops. So the animals living down in the deep reefs are ones that can survive in a dimmer, cooler world.

Scientists can dive into the deep reefs to try to learn more about these understudied places—as Rocha has—but exploring down at 100 meters requires more difficult, riskier technical diving than exploring at shallower depths. The deeper you dive, for example, the faster gases get pushed into your tissues, which imposes limits on these really deep dives.

“We have a very, very short time,” Rocha says, “And by short time, I mean five minutes. Six, seven minutes.”

Scientists can take some pictures in that time, make some measurements, or collect a few samples, but then they have to move back upwards—a process that can take hours, since they must rise slowly to avoid decompression sickness.

It is, obviously, not particularly efficient to study an ecosystem in five- to seven-minute intervals. People have also used remote-operated vehicles and submersibles to explore the deep reefs, but those have their own issues, and cameras can’t always capture all the detail you might want, or photograph more secretive, cryptic animals. So huge gaps remain in scientific knowledge about these ecosystems.