Global warming also threatens Canada's cold-water corals

The Hercules robot explores a forest of corals and sponges off the coast of British Columbia, in 2018.

Around the world, coral reefs are in decline due to anthropogenic CO2 emissions. Cold-water corals, such as those found off British Columbia, attract less public attention. Yet they are as threatened by global warming as their tropical counterparts.

Off Vancouver Island, underwater mountain ranges rise in the depths of the ocean peaceful. These remains of volcanoes are home to ecosystems of phenomenal diversity, says Robert Rangeley, scientific director of the ocean protection organization, Oceana Canada.

There are huge forests, of different types of corals, such as red tree corals or bamboo. They can be several meters high. There are also glass sponges, false starfish, octopuses, tons and tons of fish, describes the researcher, who participated in an expedition to explore 13 of these seamounts in 2018.

A remote-controlled vehicle called Hercules is deployed from the Nautilus for the first dive of the expedition.

However, these organisms play an essential role in marine ecosystems. Corals can serve as shelters and nurseries for many species of fish. They create a whole habitat, summarizes Gabriel Reygondeau, research associate at the University of British Columbia's Ocean Change Research Unit.

“If they fall, the whole ecosystem that lives on them falls. It's like taking the shell off a turtle. It's like having your home taken away from you. »

— Gabriel Reygondeau, research associate at the University of British Columbia's Ocean Change Research Unit

This octopus is one of hundreds of species that researchers observed during their expedition off the coast of British Columbia.

However, cold-water corals are particularly vulnerable to changes in their environmental conditions. Deep-sea organisms live in stable spaces, where there is almost total darkness and no diurnal/nocturnal temperature variations.

“The slightest change in temperature or pH can have an impact on resilience capacity. »

— Gabriel Reygondeau, Research Associate, Ocean Change Research Unit, University of British Columbia

Everyone thinks corals are ;is the Great Barrier Reef. It's really hard to tell ourselves that there are plenty of other species that live at depth, which are of the same family, and which are just as threatened, he adds.

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Even though they are buried more than a kilometer below the surface of the water, the accumulation of GHGs in the atmosphere has an impact on these organisms, as they warm the oceans, acidify them and reduce the amount of carbon dioxide. x27;oxygen they can carry.

The surface ocean is indeed not the only one warming; the temperature of the deep ocean, which lies more than 200 m below the water surface, is also increasing due to global warming.

In the North Pacific, temperatures have increased by about two degrees Celsius at the surface, and by about one degree Celsius at 300 meters depth compared to the period 1981-2010, found a study published in 2021.

CO2 is also naturally captured by the oceans, where it dissolves in water to form carbonic acid. When CO2 concentrations are too high, however, it lowers the pH of the water and thus increases its acidity. The hotter the water, the more this cycle is accelerated, argues Gabriel Reygondeau.

“Have you ever put acid on limescale?” Well, it makes a little white smoke and it goes pshhhht!

— Gabriel Reygondeau, Research Associate, Ocean Change Research Unit, University of British Columbia

Ocean acidification alters the calcification process of corals, which build their skeleton on limestone, explains Gabriel Reygondeau. Some of their vital growth and reproduction functions are also affected.

A halibut and redfish with yellow eyes venture into the corals of the seamounts.

This phenomenon of acidification is more marked in high latitudes than in the tropics, because cold waters are less saturated with calcium carbonate than warm waters.

According to a 2020 study , the rate of ocean deoxygenation is also unprecedented at North Pacific seamounts. We were surprised to see so many changes in oxygen. We expected changes closer to the surface, but not at 1500 m depth, says Tetjana Ross, researcher at Fisheries and Oceans Canada, who wrote the study.

It is difficult for scientists to predict how corals will react to these changing conditions. Migration to more favorable areas, as fish species already do, seems limited.

“They don't have many escape strategies. So they are very very, very in danger. »

— Gabriel Reygondeau, Research Associate, Ocean Change Research Unit, University of British Columbia

Last month, Ottawa committed to creating a protected marine area off Vancouver Island to help protect what he said is a sea floor with extraordinary characteristics.

The area concerned covers a territory of more than 133,000 square kilometers in the Pacific Ocean, approximately 150 kilometers from the west coast of Vancouver Island.

The organization Océana Canada had been campaigning for the creation of this protected area for years, alongside many First Nations. The more than 133,000 square kilometer area is home to more than 46 seamounts, according to the federal government.

This protection measure will at least reduce the cumulative pressure on these species, due to fishing and mining, explains Robert Rangeley.

However, he confirms that this will do nothing to curb ocean acidification or warming. Only limiting our greenhouse gas emissions can help, he says.