How Climate Change Threatens the Survival of Deep-Sea Coral Reefs in the North Atlantic

Did you know that Canada has coral reefs? The Great Barrier Reef is not the only lush underwater forest.

Unlike Australia’s tropical reefs, cold-water corals exist off the eastern coast of Canada. Deep-sea corals do not need sunlight to survive, can be between a few hundred to several thousand years old, and live at depths of 40 meters up to an incredible 2,000 meters. But how has climate change impacted deep-sea corals in the North Atlantic?

A 2021 issue from the Oceanography magazine entitled "Coralporosis: Ocean Acidification Leaves Deep-Sea Coral Reefs at Risk of Collapse," talks about new research published by scientists from the University of Edinburgh, Heriot-Watt University and the US National Oceanic and Atmospheric Administration (NOAA) published in 2020. The study suggests that deep-sea corals' "bones" are weakening from ocean acidification (caused by increasing carbon dioxide in the oceans). A decrease in ocean pH brought on by climate change causes deep-sea cold-water corals' foundations to become brittle.

As a result, the homes of a plethora of marine species are at risk. The team of researchers attempted to demonstrate the rapid dissolution of the corals' skeletons and noticed a similarity to osteoporosis in humans. The corals' skeleton is made of calcium and carbonate from seawater. They build new layers of skeleton on top of the older layers, which accumulate with time just like tree rings, marking time. Of course, other elements make up a coral's skeleton: strontium, magnesium, barium, and uranium.

Water temperature makes a difference in how these elements are incorporated into the skeleton. For example, when the water is warmer, some elemental levels increase, while others decrease.  The scientists studied the species Lophelia pertusa, the only species in the genus Lophelia, which can be found throughout the North Atlantic Ocean and other parts of the world, like in the Caribbean Sea, the Alboran Sea, the Mediterranean Sea, and the North Pacific. They live at depths between 80 meters and 3000 meters in a temperature range of 4°C to 12°C. The species is slow growing and depends on current patterns to spread coral larvae from one site to another.

The coral larvae are dependent on the annual weather pattern - the North Atlantic Oscillation (NAO). When the NAO is disturbed due to climate change, for example, it can cause abnormal temperatures, pressure systems, and storm patterns that can send the coral larvae toward areas they're not supposed to end up at, such as the mid-Atlantic. The reefs must exchange coral larvae to build stronger structures, but when they're isolated due to shifting ocean currents, they're at higher risk of disease and damage. The deep sea plays an important role in global climate regulation by receiving and storing heat and carbon dioxide.

However, climate-induced changes cause unnatural warming, ocean acidification, and deoxygenation of deep waters, which decreases the availability of food sources on the seafloor. Such changes will heavily affect productivity, biodiversity, and the distribution of deep-sea fauna. Coral reefs in general are of particular interest to scientists and private businesses because they contain chemicals that can be used in medicine.

For example, two deep-sea sponges contain compounds with anti-inflammatory and anti-viral capabilities, while another deep-water sponge contains potent anti-tumor resistance against human lung and breast cancer cells. It is certainly a pool of unexplored potential to advance medical knowledge, but coral mining (whether for medicine or other purposes) makes it susceptible to over-exploitation in the long run and will eventually suffer the same fate as clearcut forests.

Coral mining is a large business, with over $ 375 billion worth of coral being harvested annually for a number of purposes. For example, in the Maldives, coral is used to make limestone and a cement substitute to build houses, roads, and sea walls, as it is the only local building material, but the depletion of corals leaves the low-lying islands exposed to extreme storms caused by climate change since coral reefs act as natural sea defenses. Coral reefs are also victims of commercial fishing, which increasingly targets deeper waters and their machineries trawl the seafloor, destroying entire reef colonies.

Oil spills, such as the Deepwater Horizon incident, can also devastate these habitats, as well as ocean acidification, land-based runoff, pollutant discharges, and increased water temperatures. These reefs are home to incredible biodiversity and food sources for both marine mammals and humans. They act as natural barriers to shorelines and prevent flooding from storms, hurricanes, and cyclones. Additionally, the ocean and coastal ecosystems, such as the Great Barrier Reef, absorb CO2 from the atmosphere much faster than forests do. But when these “carbon sinks” are damaged, they release carbon back into the atmosphere, making the CO2 emissions worse.

Deep-sea coral reefs are among the planet’s oldest and most diverse ecosystems, and they are quickly deteriorating because of rising temperatures, ocean acidification, and other environmental stressors, and their extinction would have significant repercussions for the stability and health of the deep oceans. Since people cannot tolerate the extreme pressures of the deep sea, sending human exploration there is expensive, and the technology is underdeveloped, thus it is challenging to undertake coral regeneration in such deep waters. Moreover, additional research is needed to better understand the effects of climate change on deep-sea marine life in order to find the best ways to mitigate their deterioration.