Four hundred feet below the surface of the ocean there exists an aquatic world scientists call the “Twilight Zone”.
It’s a shadowy environment marking the boundary between sunlit shallow reefs and the dark abyss of the deep ocean.
Scientists from the California Academy of Sciences have been exploring this unusual environment, collecting data, photo images and sea life. The results have been impressive and it’s a certainty much of what they have collected has been unknown to science.
In 2014 academy teams accompanied other scientists on an expedition to the Cape Verde Passage in the Philippines which contains the most diversity of sea life among reefs in the “Coral Triangle” formed by the Philippines, Indonesia and New Guinea.
Financed by a grant from the National Science Foundation, the field study involved researchers from several disciplines including Terry Gosliner, the academy’s curator of Invertebrate Zoology who studies nudibranchs, the colorful sea slugs.
Other researchers including Ichthyologist Luiz Rocha and Bart Shepherd, director of Steinhart Aquarium, formed a dive team that worked in the zone observing, counting and collecting fish.
The divers returned to the area this month for a second series of dives.
Pressure within the zone is 10 times greater than at the surface. Divers wear specially adapted suits not unlike a space suit and breathe a mixture of gases containing helium to counter the effects of the deep undersea environment.
The zone represents the maximum depth humans can reach with scuba gear. To descend any deeper, researchers must use a submersible built to withstand even greater pressures.
Before they could dive, Shepherd, Rocha and other divers went through hours of training off Hawaii to be certified. It was tough work but worth it, Shepherd said.
“There’s not a lot of people in the world who have done that or can do that,” he said.
“One of the unique strengths of the academy is that it can field a team like this to do assessments on deep coral reefs.”
Once at depth, divers have only 20 minutes or so to gather specimens and other data before beginning the extremely slow ascent to the surface. The process can take up to five hours as their bodies decompress avoiding a fatal expansion bubbles in their blood streams.
The last 90 minutes is spent in relatively shallow water so the dive team must find ways to pass the time.
“That’s the hardest part for me,” Shepherd he said.
”In the initial part you are gearing up, are focused on the safety and are excited about the dive. Once you reach 200 feet, you are so in the moment you have jobs to do. But on the way back up you think ‘its 99 minutes…really’”!
While in the deep, divers stay within sight of one another and check computerized dive monitors that measure depth and tell them when they need to begin their ascent.
Collecting fish for analysis and display was another challenge given that a fish’s swim bladder could burst if brought to the surface without compensating for pressure changes.
Researchers solved the problem by inventing a cylinder- sized portable decompression chamber that maintains deep sea pressure while fish are being slowly decompressed at the surface over a period of days. Some of the fish are now on display at the aquarium.
Because new diving technology was needed to bring humans to 400 feet, the dive teams were likely the first to visit some of the areas they studied.
“One of the things that’s exciting about it is that it’s so unexplored that every dive is ripe for discovery,” he said.
Data gathered on the dives will give researchers a better idea of the deep reef ecosystem and its connection with shallower reefs, Shepherd said.
As aquarium director, Shepard is more than just a diver. His job is to develop exhibits that will educate the public and hopefully build support for reef sustainability.
“For me it’s me more about the public outreach. How do we get this message to people, “he said.
“People tend to protect shallow water reefs and it’s because if you ask someone to describe a coral reef they have a picture in their head of what a coral reef looks like.”
“If you ask someone what is the twilight zone or a mesophotic reef they can’t say that. Nobody has a picture of what is there at the bottom. “