By Catherine Wallace
Researchers at the Caper Eleuthera Institute (CEI) have been mapping the deep waters at the northern end of the Bahamian archipelago for many years, but their efforts received a boost recently when they partnered with state-of-the-art research vessel M/V Alucia.
Equipped with two manned submersibles carrying cameras and sensors, the Alucia allowed the team to journey down 800m (2,624ft) into the dark, mysterious depths of the Exuma Sound to see, monitor and sample the creatures and terrain.
For CEI research associate Brendan Talwar, it was a game-changer.
"All of our information about the depths came from dropping lines, which didn't give us very high-resolution data," he said.
"We had a very basic understanding of what was there. There is something so different and incredible about actually going down and exploring it."
Pancake batfish, swimming sea cucumbers, white-spotted catsharks and a dazzling array of jellyfish greeted the subs. When they broke the surface, the research team had a new understanding of the environment they'd been studying for so long.
The M/V Alucia, operated by ocean exploration organisation OceanX, visited CEI twice. The first mission took place over six days in April and was a learning experience for the Bahamas-based team.
"None of us had worked off a sub before, so we didn't know what it could do," said Talwar.
"We had to deal with simple things like getting our gear to be the right size and the right weight. We tried it out to see what we could actually achieve using the platform, and then we had a few months before they came back to refine what we wanted to do."
Moored off the Eleuthera coastline, the M/V Alucia attracted a lot of attention, with around 400 visitors touring the boat before the work began. Students from The Island School, an educational facility attached to CEI, and the local Deep Creek Middle School were enthralled by the vessel, which includes a helipad, fully-equipped science labs and the two manned subs.
"It blew me away," Talwar said. "The first time I went out to the ship, it seemed unreal. You feel like you are a part of something really big. It was an inspirational experience."
For that first mission, the team had the choice of two subs - the Nadir, a Triton 3300/3 sub capable of accommodating two passengers and a pilot, and the Deep Rover, a two-seater vessel fitted with a Shilling T4 manipulator, a robotic arm designed for collecting specimens and operating sampling tools. Both subs can descend to 1,000m (3,280ft).
The subs explored the rocky terrain of the Exuma Sound, which includes a vertical wall that descends down 200m (656ft) and ends in a steep slope marked with boulders, rock falls and ridges.
It was otherworldly, according to Talwar.
"There are incredible ridges that come out of the shallow water embankment and run down to 800m (2,624ft)," he said.
"Going over that in a sub feels like you are flying over a mountain range."
It took around 30 minutes to fully descend in the sub. "The light changes as you go down. You see purple, dark blues and then black" Talwar said.
"There is a bioluminescence layer, and if you turn off the lights you can see these little fireworks going off. It is beautiful and incredibly peaceful."
Between 300m (984ft) and 500m (1,640ft), on the edge of the Exuma Sound wall, the team found various species of echinoderms (starfish, sea urchins, and sea cucumbers) and a previously undocumented species of glass sponge. They also collected samples of sea cucumbers and crinoids at 630m (2,066ft).
Although it is too early to tell if the samples they collected are new species, Talwar is hopeful, saying: "We pulled up a number of invertebrates. We saw all kind of things, it just takes time to identify them. I would be very shocked if we did not find any new species."
Alongside samples, the team collected valuable footage of life on the ocean floor. They rigged up bait boxes with cameras on timers, synced with lights, to capture deep-dwelling fish such as night sharks.
Sharks were high on the agenda when the M/V Alucia returned last month.
Dr Dean Grubbs from Florida State University, which partnered with CEI on the mission, led efforts to tag a notoriously elusive deep-water predator, the bluntnose sixgill shark.
The sixgill is one of the oldest sharks in the ocean but learning more about the species has proved difficult. Tagging a sixgill shark usually involves dragging it up to the surface, putting the animal under extreme stress.
Attaching a modified speargun to the front of the Nadir and travelling down to 800m (2624ft), the scientists hoped to tag a Bahamian sixgill in the most humane way possible.
Although their efforts were unsuccessful, they came close. "The shark came right in front of the sub, but it was just a little too high up," Talwar said.
"Just putting in the legwork was great. It's never been done on a sub before at those depths."
Another key objective was to sample the water at 200-800m (656-2,624ft) to test for environmental DNA.
"When an animal swims around, it leaves little pieces of DNA behind in the water," Talwar said. "We are trying to see if environmental DNA can reveal the abundance of certain species."
The team had specially adapted bottles attached to the front of the sub that collected water. The water was then run through filters in the lab and the results cross-referenced with footage the team took from the site to see if the species caught on camera are the same as those identified from the DNA.
Talwar said the large amount of data generated by this year's missions will inform CEI's work for years to come. "From a research perspective, it provides a platform for us to move forward. It will guide us in all that we do in the deep water ecosystem in the future."
He predicted that further advances in the technology will give scientists like himself more opportunities to observe the underwater world without disrupting its inhabitants.
"It does not replace seeing it firsthand, [but] remotely operated vehicles with cameras are coming next," Talwar said.
"Something you really become aware of is the impact the sub has on the life around you. It is loud and bright. You think you are going into an alien world, but really you are the alien. As we cruise around, a lot of the life down there is moving away from us."
The Bahamas has committed to protecting 20 percent of its waters by 2020 under the Caribbean Challenge Initiative.
CEI will be sharing all the data collected from its recent underwater explorations with the Bahamas National Trust, to help inform their discussions about which areas in the archipelago are worth preserving.
"We put a lot of effort into figuring out where to site protected areas, but a lot of that effort goes into shallow-water areas," Talwar said, adding he wanted to see more of a focus on deep-water habitats.
"We want to highlight that there is ecological value down there that is not recognized," he said.
"Going down and shining a light on everything that is often forgotten or not considered was really amazing. Now when we go out to dive, I can look into the deep blue water and know exactly what's down there."
• This article first appeared on the nature news website mongabay.com.