Hundreds of meters below the ocean surface, somewhere between the dark ocean floor and the bright blue waters, lies the twilight zone.
It’s an unknown world, but in some tropical and subtropical waters coral reefs thrive. Very few scientists have ventured into these deep reefs, known technically as mesophotic coral ecosystems, meaning “intermediate light,” and many assumed that the lack of light and cold temperatures meant few species could exist there.
But a scientist has dived into the depths to show that there is much more to life there than previously thought.
“When you get up close, it’s a very colorful ecosystem,” says Luiz Rocha, a Brazilian ichthyologist (a person who studies fish) and co-director of the California Academy of Sciences’ Hope for Reefs initiative. “There are many types of fish and many of them are unknown.”
Rocha, whose studies focus on ocean life between 60 and 152 meters deep, was drawn to the twilight zone reefs for their mystery. “Every dive we do to those depths (leads to) a new discovery,” he says.
To date, it has identified some 30 new species, from a purple fairy fish named after the mythical nation of Wakanda, to Tosanoides aphrodite, a pink and yellow reef fish named after the Greek goddess of love. But his explorations in the deep sea have also shown that these reefs and the rainbow species that inhabit them are threatened. His mission is to protect them.
Entering the twilight zone is not easy. Although it could be reached by submarine, it would be a clumsy way to study fish that dart in and out of the shadows, says Rocha, comparing it to studying birds in a rainforest with a helicopter.
Instead, he dives, but the lower he goes, the more dangerous he becomes. recreational diving has a limit of 40 meters for safety reasons, but Rocha dives up to 150 meters. This requires deep concentration, intense technical training and a strong dose of courage.
“What really makes this research special is that there are only a handful of scientists in the world doing this,” he says.
Rocha usually dives in a group with two scientists and a security officer. They spend hours preparing the equipment, making sure that every part works well and that they are equipped to deal with underwater emergencies. Divers must wear breathing apparatus called rebreatherswhich recycle the gas exhaled by the diver, and a special breathing gas that contains helium and is safe for deep diving.
Going down only takes 10 to 15 minutes, depending on how steep the reef is, says Rocha, but going up can take five to six hours to allow the body to decompress.
All that effort allows him to spend between seven and ten minutes at maximum depth, where he and his team look for fish, collect DNA samples and record the number of organisms in an area. If they think they’ve found a new species, they usually trap it and bring it to the surface in a decompression chamber so they can study the specimen back in the lab.
Despite having done it dozens of times, Rocha still feels a rush of anxiety before each dive.
The deeper you go, the darker and colder the water becomes, he says. “But when we get there, we know why we’re there. When you see something that no one has seen before…it’s absolutely amazing.”
Human impacts run deep
Although the twilight zone has been explored by very few people, the effects of human activity are still evident.
Deeper-sea coral reefs were previously thought to provide refuge as they were less affected by human development and climate change. but rock proved this to be a mistake: “One of our first discoveries is that those deeper reefs are not really a refuge for shallow reef organisms. They are almost as affected as shallow reefs,” he says.
Rocha has found plastic trash and fishing gear on some of the deepest reefs and has seen the impact of overfishing and climate change. Although there is not yet enough data to determine the extent of the damage compared to shallower reefs, he says it is clear that water temperatures are also warming in deeper areas and causing reef bleaching.
Rocha hopes her research can help educate people about the twilight zone and inspire action to protect it. She works with legislators, defending the marine protected areas where these deep reefs are found. In 2019, the Hope for Reefs initiative participated in the protection of a coral reef habitat on Maricaban Islandin the Philippines, and the previous year his research served as the basis for the establishment of two protected areas in Brazil.
Rocha also works closely with local communities, collaborating with local researchers and giving newly discovered species local names. For example, earlier this year he and Maldivian biologist Ahmed Najeeb discovered a rainbow-colored fish they named Cirrhilabrus finifenmaa, or rose-veil fairyfish, after the national flower of the Maldives, a pink rose called Finifenmaa. . Rocha hopes this will “give ownership to the local population.”
Rocha believes that technology will soon advance to a point where many more people can access the twilight zone and even more species will be discovered. But his main goal is that when they do, ecosystems look the same as they do now.
“I don’t think doing science is enough,” he says. “We take many, many photographs…and we bring those stories to the surface and share them with as many people as possible.”
“For the most part, when people realize these reefs are there, they move to protect them,” he adds.