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Most people associate the word “coral” with the sun, blue skies and Australia’s Great Barrier Reef. In fact, more than half of the planet’s 5,100 species exist as “cold water corals” in the deep, dark parts of the world’s oceans.
Unlike most other animals, corals are immobile and therefore rely heavily on currents to carry tiny pieces of organic matter for food.
Over time, in some cases millions of years, cold water corals can grow to eventually form huge structures the size of a skyscraper on the seabed called “coral mounds”.
These structures are common in the northeast Atlantic at the edge of the Irish continental shelf. They can be several miles long and reach 100 meters (328 feet) or more in height – taller than any building in Ireland.
I have been studying the cold-water coral habitats off the coast of Ireland for a number of years and have found these mounds of coral and fossilized sediment to be incredibly diverse.
Some are completely covered in living coral while others have a lot of dead coral on the surface, and the mounds themselves come in very different shapes and sizes.
A place of interest is the Porcupine Bank Canyon, the largest submarine canyon on the edge of the Irish continental shelf. Dear colleagues and I wanted to understand why the coral varies so much over short distances.
To do this, we used the Irish Marine Institute’s deepwater research submersible to collect sonar data and deploy surveillance systems.
This equipment is essential for retrieving information on habitats that are nearly one kilometer (0.62 miles) below the surface. We recently published the results of our work in the Nature newspaper Scientific reports.
The images show that the corals thrive all the way to the edge of the canyon on an almost vertical cliff. Monitoring stations deployed nearby showed the currents here to be rapid, sometimes over a meter per second, the highest speed ever recorded in a cold-water coral habitat.
However, there was also more coral rubble at these sites, which may be the result of these faster currents.
We then used video footage captured by the submarine to generate 3D reconstructions of the coral habitats that we were able to analyze to understand how deep-water currents were influencing them.
Interestingly, while corals can survive these extreme conditions, it seems that they still prefer the current to slow down, as they then find it easier to feed.
As cold-water corals live in such remote areas of the planet, in the past experiments have been conducted in reservoirs in laboratories that show similar results.
As the world gets warmer, so do the oceans. Winds on the sea surface are intensifying, causing average ocean currents to accelerate by about 5% per decade since the 1990s.
It’s still unclear exactly how these huge coral mounds deep below the ocean’s surface will respond to these changing conditions, especially since coral lives on such long time scales. After all, these coral mounds grow very slowly, no more than 12 centimeters (4.7 inches) every thousand years.
Yet despite their slow-growing nature, my colleagues and I have already found that these mounds have exhibited changes in just four years, with an increase in the amounts of coral rubble and a significant decrease in a species’ cover. of particular coral.
This is why our team recently deployed the monitoring stations for another year. We’re looking for things like increased production of coral rubble or coral growth on mounds.
Ultimately, our goal is to determine how these corals will respond to these difficult and changing conditions in the long term. 
Aaron Lim, Postdoctoral Fellow, Marine Geosciences, University College Cork.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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