Climate change threaten survival of the ocean’s deep-water corals

Elizabeth GROSSMAN

What deep-water corals also reveal about the process of ocean acidification is where these changes are occurring. This information can then help us understand how climate change is affecting ocean circulation. “There are strong geographical patterns to how the oceans are acidifying,” explains John Guinotte, marine biogeographer with the Marine Conservation Biology Institute, a nonprofit based near Seattle that advocates for ocean protection. “Because colder water holds more CO2, high latitude waters at the poles are acidifying at the fastest rate,” he says. “And the Arctic is acidifying faster than the Southern Ocean.”

Environmental Laboratory

Richard Feely, chemical oceanographer at NOAA’s Pacific Marine Environmental Laboratory points out that the finely tuned polar ecosystems that are most sensitive to the impacts of excess CO2 are those farthest removed from the sources. Because the majority of the world’s industry, power plants, and other fossil fuel emissions are released in the Northern Hemisphere, atmospheric circulation sweeps these gases toward the Arctic. There the exchange of CO2 between air and sea begins its lengthy journey to the bottom of the sea.

When trying to follow CO2’s journey to deep seas where cold-water corals live, it’s important to remember that atmospheric carbon can persist for years even decades and how correspondingly long these effects play out in the ocean. Scott Doney, a marine biologist at the Woods Hole Oceanographic Institution explains that water becomes acidified where it was exposed to the surface.

As it cools and evaporates, the surface water becomes saltier and heavier and begins to sink and travel with ocean currents. This is a slow process, Doney says, so deep water can be many years removed from contact with the surface. “As this deep water sloshes up onto the continental shelf, it brings acidic water with it. And just a little extra fossil fuel carbon can put things over the edge.”

This is not good news for deep-water corals. As Guinotte explains, these beautiful and complex creatures evolved to grow in cold, deep, nutrient-rich waters, and they grow very slowly.

Northern seas, where a great many of these corals are found, are loaded with CO2. “Stony corals in the North Pacific are now surviving but not flourishing like they are in other areas of the world,” Guinotte says.

“And this could be the future if we keep pumping CO2 into the atmosphere at the rate we are.”

What Guinotte and his colleagues are now trying to determine is how the relative current carbonate saturation of different ocean areas will affect different species of deep-water coral. Part of the reason this is a key piece to understanding the cold-water coral puzzle is that different corals use different forms of calcium carbonate to build their bones and branches. There are several different types - aragonite, calcite, and high magnesium calcite and each has a different solubility under high CO2 conditions.

Changing conditions

“We don’t yet know if they’re opportunistic or species specific,” says Guinotte of the different forms of calcium carbonate. “And we don’t yet know if they (the corals that use a specific type) can adapt to changing conditions.” Given the great diversity of deep-water coral species and that so many of these species appear to be site-specific and limited in range, a change in conditions that foster a particular coral’s growth could have significant ramifications not only for the coral, but also for the other species that depend on it for habitat and nutrient cycling.

The changes we’re now seeing in ocean conditions, says Murray Roberts, a marine biologist with the Scottish Association for Marine Science, are unprecedented, and are likely to have dramatic impact for species like cold-water corals that live on a geologic timescale. Or as Lance Morgan of the Marine Conservation Biology Institute puts it: “Ocean acidification is a geologic time showstopper.” If we lose these corals, we may lose essential deep-sea anchors of biodiversity. In doing so, we will also lose the longest-living records of Earth’s changing climate and chemistry, fossils that may reveal key details to understanding how the planet will respond to the changes now underway.

Deep-sea corals

So what do we do? Can we stop the destruction? If so, how?

Morgan and Guinotte remind me that while we’re busy burning coal and gas, loading the atmosphere with CO2 and other greenhouse gasses at a great clip, what destroys deep-sea corals even faster than ocean acidification is bottom trawling. This type of fishing gear is dragged over the sea floor, literally bulldozing whatever it encounters.

Unlike atmospheric carbon, which takes years or decades to dissipate, bottom trawling can stop immediately. With the aim of implementing an international ban on deep-sea bottom trawling, the Marine Conservation Biology Institute co-founded the Deep Sea Conservation Coalition and began UN negotiations among fishing nations. No such agreement has yet been reached, but there are now marine reserves and protected areas around the world where bottom trawling is prohibited.

“Resiliency is key,” Morgan says. “Reserves make a lot of sense when it’s hard to nail down which incremental stress is going to be the straw that breaks the camel’s back.” Reserves, he explains, can help preserve a full complement of biodiversity while limiting the introduction of additional elements of stress.

Closing sensitive benthic habitat to destructive bottom trawling will be essential to preserving corals and fish habitat, says Guinotte.

“No matter how remote the location, if you talk to scientists who go down in submersibles, there is trawler evidence.” Yet, he says, “the devil is in the details,” explaining that United States National Marine Sanctuaries are “multiple use” areas, with regulations specific to each area. In some, trawling and fishing are restricted, but in others they are not. Some of these regulations are federal, some are state, and some more local.

Protection Agency

Meanwhile, in late January 2009, the US Environmental Protection Agency agreed to review how ocean acidification may be addressed under the federal Clean Water Act.

At the same time, a panel of over 150 scientists working with UNESCO issued a statement calling for immediate action by international policy-makers to reduce CO2 emissions to avoid severe acidification damage to marine ecosystems.

“There is no magic bullet to turn around ocean chemistry,” cautions Guinotte. “So we have to look at creating protected areas and refugia.”

Listening to these scientists talk about deep-water corals, I find myself thinking about fossils in a race against the clock. The pace at which we are changing ocean chemistry is happening in a time frame utterly alien to these mind-bogglingly intricate deep-sea corals.

When I ask Murray Roberts why it is so important to understand what’s happening to these animals hardly anyone will ever see, he asks a question back: “Why does our generation have a right to stop the next generation from having a positive environment? Some of these corals have never been seen before. Does our generation have the right to remove them?”

- Third World Network Features