A beautiful cold water coral. This is known as a soft coral, the green-ish branches supporting the easily identifiable nematocysts. (Nick Hobgood)

If you’ve ever seen a photo of a lively coral reef, or have had the opportunity to see one of these miraculous ecosystems with your own eyes, you’ll be aware of their dazzling colours, rich diversity and great beauty. But they aren’t limited to the tropics. In fact, there are beautiful, ancient corals to be found in some of the deepest, coldest parts of the world’s oceans.

Cold water corals (or deep-sea corals) can be found anywhere from 35 metres to the abyssal plain at depths of 6,000 metres, though the largest number congregate at the continental shelf and slope at a slightly more agreeable 200-2000m. Unlike tropical corals, they must survive with very little light, an environmental characteristic they’ve had to adapt to in a way which may impress you.

Friendless corals

An example of some stinging nematocysts! (ARKive)

Zooxanthellae are a microscopic alga which live inside tropical coral polyps. Their symbiotic relationship with the polyp keeps both organisms alive: the zooxanthellae photosynthesise and provide the coral with sugars to grow. But in such low light conditions, cold-water corals have none of these zooxanthellae, so how do they survive?

The cold-water corals, as is to be somewhat expected from a creature that lives in the dark, cold underbelly of the oceans, foregoes this friendship in favour of tiny tentacles covered in stinging cells called nematocysts. These nematocysts are the same stingers that make jellyfish such an unpleasant experience for us, but for the prey of the cold-water corals they’re even worse. Using these nematocysts, the corals sting and stun its prey (usually zooplankton or small crustaceans), injecting a poison that gives the coral time to push it into its mouth and digest the prey.

Not indestructible

As fascinating and beautiful as cold-water corals are, they’re unfortunately very vulnerable to anthropogenic interference. Because they don’t build reefs, instead preferring to stand alone or at the very most clump together, it’s easy for them to be damaged or even wiped out entirely by trawlers. Deep sea trawling has been cropping up in science news often since the early 2000s, when it was discovered the massive nets were tearing up corals on the sea bed, much like in the tropics.

The site of a cold water coral community near Australia before and after trawling. (Keith Sainsbury)

Another threat to these ancient environments is ocean acidification. As the carbon dioxide content of the oceans increases, the structure of the coral warps and changes, making it fragile and weak. This is bad news not only for the corals but the hundreds of species that rely on cold-water corals to survive, such as squat lobsters and rockfish and… us?

Help them help us

Despite their remoteness, there’s one thing you really should know about cold-water corals: they’re helping us too! In the medical field, scientists and doctors are learning a lot from cold water coral and the chemicals that make them. Some corals have been shown to contain compounds that are antiviral, or can reduce swelling. Not to mention the immunosuppressant compound -discodermolide found in the cold-water coral Discodermia dissolute. It stabilises potential tumours and could one day contribute to a cure for breast and lung cancer. It also helps strengthen neurons, which could prove invaluable to Alzheimer research in future years.

With their beauty and use, cold-water corals are definitely important worth conserving. They need protecting strictly and soon, or else we may wipe them out before we even have chance to learn all their secrets.


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