Scientists discover five new species of black coral living thousands of feet below the ocean’s surface near the Great Barrier Reef

The Research Brief is a short account of interesting academic work.

The big idea

Using a remote-controlled submarine, my colleagues and I have discovered five new species of black coral living at a depth of 760 meters below the surface of the Great Barrier Reef and Coral Sea off the coast of Australia.

Black corals can be found growing both in shallow water and to depths of over 26,000 feet (8,000 meters), and some individual corals can live for over 4,000 years. Many of these corals are branched and look like feathers, fans or bushes, while others are straight like a whip. Unlike their colorful shallow-water cousins ​​that rely on the sun and photosynthesis for energy, black corals are filter feeders and eat tiny zooplankton that are abundant in deep waters.

The team of researchers collected 60 black coral specimens in 31 dives using a remote-controlled submarine.

In 2019 and 2020, a team of Australian scientists and I used the Schmidt Ocean Institute’s remotely operated vehicle, a submarine called the SuBastian, to explore the Great Barrier Reef and Coral Sea. Our goal was to collect samples of coral species that live in deep waters from 130 feet to 6,000 feet (40 to 1,800 meters). In the past, the corals from the deep parts of this region were harvested using dredging and trawling methods which often destroyed the corals.

Our two expeditions were the first to send a robot into these particular deep-sea ecosystems, allowing our team to safely view and harvest deep-sea corals in their natural habitats. Over the course of 31 dives, my colleagues and I collected 60 specimens of black coral. We will carefully remove the corals from the sandy floor or coral wall using the rover’s robotic claws, place the corals in a temperature-controlled, pressurized storage box, and then bring them to the surface. We would then examine the physical characteristics of the corals and sequence their DNA.

Among the many interesting specimens were five new species, including one we found growing on the shell of a nautilus more than 760 meters below the ocean’s surface.

The researchers used their rover’s robotic arm to collect more than 100 samples of rare corals and brought them to the surface for further study.
Jeremy HorowitzCC BY-ND

Because matter

Similar to shallow-water corals that build colorful reefs filled with fish, black corals serve as important habitats for fish and invertebrates to feed and hide from predators in what is otherwise a mostly barren seabed. For example, a single colony of black coral collected by researchers in 2005 off the coast of California was home to 2,554 individual invertebrates.

Recent research has begun to paint a picture of a deep sea containing far more species than biologists previously thought. Considering that there are only 300 known species of black corals in the world, finding five new species in one generic location was very surprising and exciting for our team. Many black corals are threatened by illegal harvesting for jewellery. To pursue intelligent conservation of these fascinating and hard-to-reach habitats, it is important that researchers know which species live at these depths and the geographic ranges of which species.

A large white tree-like coral underwater.
Black corals don’t form large reefs like shallow corals, but individuals can get quite large, like this one Dendrochristos antipaths found off the coast of California and serves as a habitat for thousands of other organisms.
Mark Amend/NOAA via Wikimedia Commons

What we don’t know yet

Every time scientists explore the deep sea, they discover new species. Simply exploring more is the best thing researchers can do to fill the knowledge gaps about what species live there and how they’re distributed.

Because so few deep-sea black coral specimens have been collected and so many unknown species are likely still out there, there’s also a lot to learn about the coral evolutionary tree. The more species biologists discover, the better we’ll be able to understand their evolutionary history, including how they survived at least four mass extinction events.

What’s next

The next step for my colleagues and I is to continue exploring the ocean floor. Researchers have yet to collect DNA from most known species of black coral. On future expeditions, my colleagues and I plan to return to more deep coral reefs in the Great Barrier Reef and Coral Sea to continue learning more about and better protecting these habitats.

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