Hundreds of feet below the ocean's surface, somewhere between the dark ocean floor and the bright blue shallows, lies the twilight zone.
It's a world of the unknown, but in some tropical and subtropical waters coral reefs thrive. Very few scientists have ventured to these deep reefs, known technically as mesophotic coral ecosystems, meaning "middle light," and many assumed that the lack of light and chilly temperatures meant few species could exist there.
But one scientist has been diving into the inky depths to show there's much more to life there than was first thought.
READ MORE: Seven whales caught up in Australian shark nets this season
"When you get up close, it's a very colourful ecosystem," says Luiz Rocha, Brazilian ichthyologist (a person who studies fish) and co-director of the Hope for Reefs initiative at the California Academy of Sciences.
"There's many different kinds of fish and many of them are unknown."
Rocha, whose studies focus on ocean life between 200 and 500 feet deep, was attracted to twilight zone reefs because of their mystery.
"Every dive we do to those depths (leads to) a new discovery," he says.
To date, he has identified around 30 new species – from a purple fairy wrasse named after the mythical nation of Wakanda, to the Tosanoides aphrodite, a pink and yellow reef fish named after the Greek goddess of love.
But his deep-sea explorations have also proven that these reefs and the rainbow-hued species that roam them are under threat. His mission is to protect them.
READ MORE: Body of another great white shark killed by 'serial' killer whales washes up in South Africa
Diving in
Entering the twilight zone is no easy feat. While it could be reached by submarine, this would be a clumsy way to study fish that flit in and out the shadows, says Rocha, comparing it to studying birds in a rainforest with a helicopter.
Instead he scuba dives, but the deeper he descends the more dangerous it becomes. Recreational diving is capped at 130 feet (about 40 metres) for safety reasons, but Rocha dives as far as 500 feet (152m). To do this requires deep concentration, intense technical training and a strong dose of bravery.
"What really makes this research special is that there's only a handful of scientists in the world doing this," he says.
Rocha usually dives in a group with two scientists and one safety officer. They spend hours preparing the kit, ensuring every piece of equipment is functioning well and that they are equipped to deal with underwater emergencies.
The divers must use rebreathers, which recycle the gas exhaled by the diver, and a special breathing gas containing helium that is safe for deep dives.
READ MORE: Couple loses almost $40,000 after falling victim to real estate scam
Getting down takes just 10 to 15 minutes depending on how steep the reef is, says Rocha, but the ascent can take five to six hours to allow the body to decompress.
All that effort gives him just seven to 10 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 have found a new species, they usually catch it and carry it up 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 the pangs of anxiety before each dive.
The deeper you go, the darker and colder the water gets, he says. "But when we get there, we know why we're there. When you see something that nobody has ever seen before … it's absolutely amazing."
READ MORE: Red-eyed Finnish PM apologises after party video, kissing photo
Human impacts run deep
While the twilight zone has been explored by very few people, the effects of human activity are still apparent.
Previously it was thought that coral reefs in deeper waters could provide a refuge as they are less affected by human development and climate change.
But Rocha proved this wrong: "One of our first discoveries is that those deeper reefs are really not a refuge for shallow reef organisms. They are almost as impacted as the shallow reefs are," he says.
He has found plastic trash and fishing gear in some of the deepest reefs and has observed the impact of overfishing and climate change.
While there is not yet enough data to determine the scale of the damage compared to shallow reefs, he says it is clear that water temperatures are warming in the deeper zones too and causing reefs to bleach.
Rocha hopes that his research can help to educate people about the twilight zone and inspire action to protect it. He works with policymakers, making the case for marine protected areas where these deep reefs lie.
In 2019, the Hope for Reefs initiative was involved in the protection of a coral reef habitat on Maricaban Island in the Philippines, and the year before their research informed the establishment of two protected areas in Brazil.
READ MORE: Russian rocket attack kills 15 on Ukraine Independence Day
Rocha also works closely with local communities, collaborating with local researchers and giving local names to newly discovered species.
For instance, earlier this year he and Maldivian biologist Ahmed Najeeb discovered a rainbow-colored fish which they named Cirrhilabrus finifenmaa or rose-veiled fairy wrasse, after the national flower of the Maldives, a pink rose called Finifenmaa.
Rocha hopes this will "give ownership to the local people."
Rocha believes that technology will soon advance to a point that gives many more people access to the twilight zone and even more species will be discovered. But his main goal is that when they do, the ecosystems will look the same as they do now.
"I don't think it's enough just to do the science," he says. "We take many, many photographs … and we bring those stories back up to the surface and we share it with as many people as possible."
"For the most part, when people realise that those reefs are there, they move towards protecting them," he adds.
