Undersea mountain ranges rise from the depths of the Pacific Ocean off Vancouver Island. These remains of volcanoes are home to phenomenally diverse ecosystems, says Robert Rangeley, scientific director of marine conservation organization Oceana Canada.
There are huge forests with different types of coral, such as red tree coral or bamboo. They can grow several meters high. There are also glass sponges, false starfish, squid, tons and tons of fish, says the researcher, who took part in a 2018 expedition to study 13 of these seamounts.
A remote-controlled vehicle called the Hercules is used by the Nautilus for the expedition’s first dive.
Photo: Seamount Expedition Partners in the Northeast Pacific
However, these organisms play an essential role in marine ecosystems. Corals can serve as a shelter and nursery for many species of fish. They create an entire habitat, summarizes Gabriel Reygondeau, an associate researcher at the University of British Columbia’s Ocean Change Research Unit.
“When they fall, the entire ecosystem that lives on them falls. It’s like taking the shell off a turtle. It’s like taking your home away from you. »
— A quote from Gabriel Reygondeau, Research Associate at the University of British Columbia’s Ocean Change Research Unit
This octopus is one of hundreds of species the researchers observed during their expedition off the coast of British Columbia.
Photo: Ocean Exploration Trust, Seamount Expedition Partner in the Northeast Pacific
However, cold-water corals are particularly vulnerable to changes in their environmental conditions. Deep-sea organisms live in stable spaces where it is almost completely dark and without diurnal/nocturnal temperature fluctuations.
“The slightest change in temperature or pH can affect resilience. »
— A quote from Gabriel Reygondeau, Research Associate, Ocean Change Research Unit, University of British Columbia
Everyone thinks coral is the Great Barrier Reef. It’s really hard to say that there are many other deep-dwelling species that belong to the same family that are just as threatened, he adds.
Altered deep oceans
Despite being buried more than a kilometer below the surface of the water, the accumulation of greenhouse gases in the atmosphere affects these organisms as they warm the oceans, acidifying them and reducing the amount of oxygen they can carry.
Indeed, the surface ocean is not the only one warming; The temperature of the deep sea, which lies more than 200 m below the water surface, is also rising as a result of global warming.
In the North Pacific, compared to the 1981-2010 period, temperatures have increased by about 2 degrees Celsius at the surface and by about 1 degree Celsius at 300 meters below ground, according to a study published in 2021.
CO2 is also naturally captured by the oceans, where it dissolves in water to form carbonic acid. However, excessive CO2 concentrations lower the pH value of the water and thus increase its acidity. The hotter the water, the more this cycle accelerates, argues Gabriel Reygondeau.
“Have you ever put acid on limestone? Well it makes a little white smoke and it goes pshhhht! »
— A quote from Gabriel Reygondeau, Research Associate, Ocean Change Research Unit, University of British Columbia
Ocean acidification changes the calcification process of corals, which build their skeleton on limestone, explains Gabriel Reygondeau. Some of their vital functions of growth and reproduction are also affected.
A halibut and a yellow-eyed scorpionfish venture into the corals of the seamounts.
Photo: Ocean Exploration Trust, Seamount Expedition Partner in the Northeast Pacific
This acidification phenomenon is more pronounced at high latitudes than in the tropics because cold water is less saturated with calcium carbonate than warm water.
According to a 2020 study, the ocean’s oxygen depletion rate is also unprecedented at seamounts in the North Pacific. We were surprised to see so many changes in oxygen levels. We expected changes closer to the surface but not at 1500m depth, testifies Tetjana Ross, a researcher at Fisheries and Oceans Canada who wrote the study.
Protected areas can help, but they cannot solve everything
It is difficult for scientists to predict how corals will respond to these changing conditions. Migration to more favorable areas, as fish species are already doing, appears to be limited.
“They don’t have many escape strategies. So you are in very, very, very danger. »
— A quote from Gabriel Reygondeau, Research Associate, Ocean Change Research Unit, University of British Columbia
Last month, Ottawa pledged to create a marine sanctuary off Vancouver Island to help protect what it calls a seabed of exceptional properties.
The affected area covers an area of more than 133,000 square kilometers in the Pacific Ocean, approximately 150 kilometers from the west coast of Vancouver Island.
Photo: Fisheries and Oceans Canada
The organization Océana Canada, along with many First Nations, has been campaigning for the creation of this protected area for years. According to the federal government, the area, which is more than 133,000 square kilometers, is home to more than 46 seamounts.
This conservation measure will at least reduce the cumulative pressure on these species from fishing and mining, explains Robert Rangeley.
However, he confirms that this will do nothing to stop ocean acidification or warming. Only limiting our greenhouse gas emissions can help, he says.