Most people associate the word “coral” with the sun, blue sky and the Great Barrier Reef of Australia. In fact, more than half of the planet’s 5,100 species exist as “cold water corals” in dark, deep parts of the world’s oceans.
Unlike most other animals, corals are immobile and therefore rely heavily on currents to transport small pieces of organic material for food.
Over time, in some cases millions of years, cold-water corals can grow to form, at the bottom of the sea, huge skyscraper-sized structures called “coral mountains.”
These structures are common in the Northeast Atlantic on the edge of the Irish continental shelf. They can be several miles long and reach 100 meters in height or more, taller than any building in Ireland.
I have been studying cold water coral habitats on the coast of Ireland for a number of years and have found that these fossilized coral and sediment mounds are incredibly varied.
Some are completely covered with live coral, while others have many dead corals on the surface, and the same mounds have very different shapes and sizes.
One of the sights is the Porcupine Bank Canyon, the largest submarine canyon on the shores of Ireland’s continental shelf. My classmates and I wanted to understand why the coral there varied so much over short distances.
To do this, we used deep-sea submersible research from the Irish Marine Institute to collect sonar data and deploy monitoring systems.
This equipment is essential for retrieving habitat information that can be found almost one kilometer (0.62 miles) below the surface. We recently published the results of our work in the Nature magazine Scientific reports.
The images show the corals thriving at the edge of the canyon on an almost vertical cliff. Control stations deployed nearby showed that currents here were fast, sometimes exceeding one meter per second, the highest speed ever recorded in a cold-water coral habitat.
However, there was also more coral debris in these places, which could be the result of these faster currents.
We then used video images 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, although corals can survive these extreme conditions, they still seem to prefer it when the current slows down, as they find it easier to feed.
Because cold-water corals live in such remote parts of the planet, experiments have been conducted in laboratory tanks in the past that show similar results.
As the world warms, so will the oceans. Winds above the sea surface are becoming stronger, causing average ocean currents to accelerate by about 5 percent per decade since the 1990s.
It is still unclear how these huge coral mounds in the depths of the ocean will respond to these changing conditions, especially because coral lives on such long scales. After all, these coral mounds grow very slowly, no more than about 12 centimeters (4.7 inches) every thousand years.
Although, despite their slow-growing nature, colleagues and I have previously found that these mounds have undergone changes for only four years, with an increase in the amount of coral debris and a significant decrease in coral cover. ‘a particular coral species.
That’s why our team has recently deployed control stations for another year. We are looking for things like increased coral debris production or coral growth in mounds.
Ultimately, our goal is to determine how these corals will respond to these difficult and changing conditions in the long run. 
Aaron Lim, postdoctoral researcher, marine geoscience, University College Cork.
This article is republished from The Conversation under a Creative Commons license. Read the original article.