Most people associate the word “coral” with sunshine, blue skies and Australia’s Great Barrier Reef. In fact, more than half of the 5,100 species on the planet exist as “cold water corals” in the deep and dark parts of the world’s oceans.
Unlike most other animals, corals are stable and therefore rely on currents to feed small pieces of biological material in very small amounts.
Over time, in some cases millions of years, cold water corals may eventually become huge skyscrapers on seabeds called “coral mounds”.
These structures are common in the Northeast Atlantic on the edge of the Irish continental shelf. They can be several kilometers long and reach a height of 100 meters (328 ft) or more than any building in Ireland.
I have been studying cold water coral habitats off the coast of Ireland for many years, and have found that these mounds of fossil corals and sediments are incredibly diverse.
Some are completely covered with living coral, while others have a lot of dead coral on their surface, and the mounds themselves are very different shapes and sizes.
Ireland has the largest submarine valley bordering the continental shelf, a place of interest. Colleagues and I wanted to understand why the coral there is so different at short distances.
To do this, we used the Irish Marine Institute’s Deep Water Research to gather sonar data and deploy monitoring systems.
This device is required to obtain information from the residence that can be found approximately one kilometer (0.62 mi) below the surface. We have recently published the results of our work Nature magazine Scientific report.
Images show that the corals are visible on a nearly steep cliff at the very edge of the valley. Surveillance stations stationed nearby showed currents were fast, sometimes exceeding one meter per second, sometimes the highest speed recorded in cold-water coral habitats.
Nevertheless, there were more coral debris at these sites, which may have been the result of these fast currents.
We then used video footage captured by the submarine to generate 3D reconstructions of coral habitats, which we could analyze to understand how deepwater currents were affecting them.
Interestingly, while the cores can survive these extreme conditions, it appears that they still prefer it when the current slows down because then they are easier to feed.
As cold-water corals live in such remote parts of the planet, previous experiments have been carried out in tanks in laboratories that show similar results.
As the world warms, so will the oceans. Winds are strengthening on the sea surface, causing average sea currents to rise by about 5 percent per decade since the 1990s.
It is still unclear how these giant mounds of coral deep beneath the ocean surface will respond to these changing conditions, especially since the coral lives on such long time scales. Eventually, these coral mounds grow very slowly, not exceeding only 12 centimeters (4.7 in) every thousand years.
Yet despite their slow-growing nature, colleagues and I have previously found that these mounds have exhibited changes in only four years, with increasing amounts of coral debris and significant reductions in coverage of a particular coral species.
That is why our team has recently deployed monitoring stations for another year. We are looking for things like increasing the production of coral debris or the growth of coral on mules.
Finally, our objective is to determine how these cores will respond to these difficult and changing circumstances in the long run.
Aaron Lim, Post-Doctoral Researcher, Marine Geoscience, University College Cork.
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