Imagine holding a flashlight above your desk and shining it down at the surface. The area it lights up is pretty small. The beam produces a tightly contained circle. Now, imagine climbing onto the roof of your house and pointing that same flashlight down toward the ground. A much larger area brightens. You can see a lot more.
“That’s sort of what we’re doing with sound,” says Derek Sowers, mapping operations manager for the Ocean Exploration Trust and lead author of a study detailing how scientists just mapped the largest known deep-sea coral reef in the world. “If you can picture, underneath a vessel, we have mounted on the hull a fan of transducers that look out broadly in each direction. It’s painting the seafloor.”
The newly documented reef covers an area larger than Vermont and it stretches offshore from South Carolina to Florida. It’s called a deep-sea reef because it grows where sunlight cannot reach. This reef was documented at depths ranging from 655 feet to 3,280 feet—more than half a mile below the surface.
Similar to coral reefs where boaters often snorkel in tropical destinations, this deep-sea reef is fragile. However, it’s different in the way it develops. It’s built of filter-feeding corals. There’s no photosynthetic algae here. Instead, the deep-sea corals get energy from particles floating in the water, in darkness and cold, well below the thermocline. And yet, the reef is bursting with biodiversity that has adapted to the harsher environment. Scientists documented swordfish, hake, skates, sharks, eels, crabs, squat lobsters and more making use of the habitat.
“The corals are providing that structure for other things to grow, and on all the nooks and crannies, for other creatures to forage and hide from predators,” Sowers says. “They are an important part of the food web.”
The news with this study is not that deep-sea coral exists, but instead that this kind of reef can be so big. Back in the 1960s, the first large cold-water coral mounts were documented off the Southeast U.S. What today’s scientists did was spend three years using modern underwater mapping technology to create 3D images of the ocean floor, filling in gaps that existed from previous mapping efforts. The difference in what they can see with today’s tech, Sowers says, is similar to seeing a fuzzy image of a building in a Google Earth satellite image versus seeing the same building up close in sharp detail.
Overall, the researchers synthesized bathymetric data from 31 multibeam sonar mapping surveys, the largest of which were led by the National Oceanographic and Atmospheric Administration’s Ocean Exploration. Its mission is to explore the ocean floor for national benefit. This particular research created a nearly complete map of the seafloor of the Blake Plateau, which lies about 100 miles off the Southeast coastline. The core area of high-density mounds that researchers documented is up to 158 miles long and 26 miles wide. Scientists nicknamed the largest area of deep-sea coral Million Mounds.
“We’ve had the technology for some time to do this. The limitation to explore these deep-sea areas is funding and ship time,” Sowers says. “You need the vessels equipped with this technology, and you need the time to go do it.”
The vessel that supported most of the researchers’ work was NOAA’s Okeanos Explorer. It’s a converted U.S. Navy ship that’s 224-feet long and about 42-feet wide. Instead of its hull having one transducer, like a sportfishing yacht might have, there’s an array of transducers on centerline for the transmit ping, along with a separate array of receiver transducers from port to starboard. “You can’t actually put a deep-water array on a small vessel,” Sowers says. “It won’t fit.”
It also would cost more than the boat. In this case, taxpayers foot the bill for the research, with at-sea time costing about $50,000 per day, Sowers says. “We’re mapping 24 hours a day. There’s no downtime,” he stresses. “We’re trying to get as much science done when we’re at sea as possible.”
The effort is important for several reasons, he adds. First, because humans have only mapped about 25 percent of the world’s oceans with this type of technology. Scientists know that deep-sea corals exist all around the planet, but nobody knows how much of it is out there, or precisely where it’s located. These gaps in human knowledge, he says, make it impossible to protect the reefs from damage that can come from things like laying cables or pipelines deep underwater.
“We know that ecologically, they’re very important, so it’s important that we figure out the global distribution of these habitats, and then protect them,” Sowers says.
Conservation officials, he adds, draw maps to create protected areas using the best-known information at the time. “A lot of the areas where we mapped the corals, they have some protection from disturbances,” Sowers says, adding that “there was a good number of mounds outside that existing area.”
In other words, the current conservation maps for this part of the East Coast may need to be redrawn.
“To me, the bottom line is that we can’t manage or protect what we don’t know about,” Sowers says. “That’s why this type of ocean exploration is important.”
This article was originally published in the April 2024 issue.
