Acidification Is ‘Fundamentally Altering’ Oceans (Fourth in a series)
*Note to readers: With CERF’s biennial conference in Portland, Oregon, only a few weeks away, we examine how increased ocean acidification and the development of hypoxic waters along the West Coast are affecting the region’s shellfish, and the implications of ocean acidification for coastal waters, in a fourth and final article about Pacific Northwest estuaries. The third article, “Adapting to Climate Change,” discussed management options for addressing climate change in the Pacific Northwest, with a special focus on wind energy production along the Columbia River (CERF June 2009). The second article, “Diversity of Pacific Northwest Estuaries,” highlighted some of the habitats found in estuaries from Humboldt Bay, California north to coastal Washington, Puget Sound and the Fraser River (CERF February 2009). The first article, “Pacific Northwest Estuaries Were Born of Fire and Ice,” discussed the physical and geological setting of northwest estuaries (CERF October 2008).
The series of articles is coordinated by John Bragg, coastal training coordinator for the South Slough National Estuarine Research Reserve in Charleston, Oregon.
In 2005 oyster growers in Willapa Bay, Washington, took it in stride when their oysters failed to reproduce, but as successive brood also failed in 2006, 2007 and 2008, the oystermen went looking for an answer. Even as they watched, the wave of deaths spread to Oregon, where in Netarts, a tiny seafront town, the epidemic struck a shellfish hatchery that supplies oyster-growers up and down the West Coast. Nearly four-fifths of the hatchery’s brood died. University and industry scientists scrambled into the field to search for answers. What was causing such catastrophic losses?
Commercial harvest of Pacific oysters (Crassostrea gigas) in the Pacific Northwest was worth $111 million in 2005, when the region accounted for three-fourths of the West Coast’s shellfish production. West Coast oyster farms provide more than 3,000 family-wage jobs in rural coastal communities from northern California to Puget Sound, where other opportunities for work are limited. Including service businesses and suppliers, the Pacific Coast Shellfish Growers Association estimates the total economic contribution of West Coast shellfish farming to be $278 million annually. But if the trend of the past four years continues, the industry faces an $83 million loss – nearly a third of its value.
As the losses mounted in 2006 and 2007, attention first focused on a bacterium, Vibrio tubiashii, as an immediate source of trouble. Vibrio infects shellfish larvae and juveniles, and can be lethal. High levels of Vibrio were found in the oyster hatchery in 2006 and 2007. Where there had been previous, sporadic outbreaks, now, it seemed, the bacteria were able to out-compete other more-benign species.
About the same time—2007—a team of researchers aboard an Oregon State University research vessel was studying carbon cycles in waters along the West Coast. Burke Hales, an associate professor of chemical oceanography at OSU and a member of the research team, said the researchers noted extremely high CO2 levels in the upwelled source waters. Carbon dioxide, when dissolved in water, reacts to form carbonic acid which lowers the pH of the seawater and consumes alkaline carbonate ions.
“Carbonate ions (CO3=) are a key part of the calcium carbonate (CaCO3) mineral shells that numerous marine organisms, including oysters, depend on through various life stages,” Hales said. “While most of the elevated CO2 was from natural decomposition processes that happen in the ocean interior while upwelled water was enroute to the upwelling areas, a small portion originated from the invasion of atmospheric CO2 due to rising atmospheric CO2 levels. This small additional contribution pushed upwelled waters over the corrosion threshold for aragonite, a common mineral form of calcium carbonate.”
Further complicating matters is the apparent increase in frequency and intensity of hypoxic conditions along the Oregon coast. Hypoxic zones have been documented occurring off the central and northern Oregon coast since 2000, stressing, though not necessarily killing, populations of many marine creatures, and sparking reports of “dead zones” in the news. Hales said hypoxic conditions are always a threat off the Oregon coast, since upwelled waters are not only low in oxygen when they reach the coast, but they also contain abundant dissolved nutrients that fuel phytoplankton blooms. When these blooms die off, the remnants sink into deeper waters and decompose. The decomposition consumes oxygen and produces CO2, resulting in even more corrosive conditions. It’s a direct link between increased hypoxia and the corrosiveness of the upwelled waters off the Oregon coast.
The Pacific Northwest region is one of the world’s great upwelling zones. Upwelling occurs during summers when winds blow out of the north, driving surface waters away from shore and drawing up dense, cold water from the shelf to replace it. In wintertime the winds become southerly, the surface water is pushed ashore, and the dense, cold water sinks back into the ocean depths. Summer upwelling is the basis of marine food webs in the northeastern Pacific Ocean and is seen as both an ecologic and economic boon. Upwelled water is laden with nutrients such as nitrate, phosphate, and silicate. The water reaches the surface near the shore, where photosynthesis triggers the production of massive blooms of phytoplankton, usually dominated by fast-growing diatoms. This in turn fuels the webs of food organisms that ultimately grow tuna, salmon and other sea life, and feed humans as well. Since upwelling depends on persistent north winds, it can occur in fits and starts from May through September, but in years when upwelling fails altogether, lots of fish and seabirds die.
In July Hales discussed the team’s findings during a presentation at the Oregon Institute of Marine Biology’s Summer Lecture series in Charleston, Oregon. Hales and his colleagues (Richard A. Feely and Christopher L. Sabine, of NOAA’s Pacific Marine Environmental Laboratory in Seattle, Washington; Debby Ianson, of Fisheries and Oceans Canada in Sidney, British Columbia; and J. Martin Hernandez-Ayon, Instituto de Investigaciones Oceanologicas at the University of Baja California, in Ensenada, Mexico) studied sea water samples collected from the Queen Charlotte Sound to Baja California. They found corrosive sea water within 20 miles of the coast – and showed for the first time that this condition was significantly influenced by rising atmospheric CO2. In one case the corrosive water was found as near as four miles from shore.
When atmospheric carbon dioxide is absorbed in sea water, a series of reactions inevitably takes place that results in the release of hydrogen ions, increasing the acidity of the sea water and the consumption of carbonate ions. Adult oysters build their shells using calcite, the least soluble of the calcium carbonate minerals. Larval oysters, on the other hand, form their shells from aragonite, a much more soluble form of calcium carbonate. Hales said larval oysters that are being exposed to the acidic waters occurring over the shelf are unable to make aragonite shells and without shells, die. That’s what has been happening at the oyster hatchery in Netarts.
“Alan Barton at Whiskey Creek Shellfish tells me that after hatching, the juvenile oysters appear physiologically fine. They grow, they metabolize, but they never grow their shells. They can do that for about two weeks and then the whole colony dies,” Hales said.
Ocean acidification is fundamentally altering the biological and geochemical processes of the sea. Ocean acidification is not a side-effect of climate change, but rather a wholly separate problem resulting from the presence of too much CO2 in the atmosphere. Hales offered a definition: “It’s the name given to changes in carbonate chemistry and the acid-base balances in the ocean that result from invasion of anthropogenic CO2 from the atmosphere.”
Acidification relates directly to the concentration of atmospheric CO2. According to NOAA, the release of CO2 from human industrial activity has raised the level of atmospheric CO2 from about 280 to 385 parts per million (ppm) within the last century. The level of atmospheric CO2 is now higher on Earth than at any time in the last million years or so, probably higher than in the last 20 million years, and is expected to keep rising at an increasing rate. Since CO2 readily dissolves in seawater, the pH of ocean surface waters has already decreased by about 0.1 pH, from an average of about 8.2 to 8.1 since the industrial revolution. NOAA estimates that future atmospheric CO2 concentration could reach more than 500 ppm by mid-century and exceed 800 ppm by 2100, based on the Intergovernmental Panel on Climate Change’s CO2 emission and ocean-atmosphere models. That would mean an additional decrease in the pH of surface water of approximately 0.3 pH units by 2100.
The bad news is that the water that upwells is likely to become even more acidic over time. The waters upwelling today were last exposed to air roughly 50 years ago, at a time when atmospheric carbon was at a much lower level. The lag represents the amount of time it takes the sea water to become dense enough and cold enough to sink in the western north Pacific, circulate around the sub-surface waters of the Pacific basin, and return to the Pacific Northwest coast to upwell again. Water exposed to the atmosphere today will return to the surface again around 2059.
In an interview with Elizabeth Kolbert of The New Yorker (published July 9, 2009 in Yale Environment 360), Jane Lubchenco, a marine ecologist formerly on the faculty of Oregon State University and now administrator of NOAA, called ocean acidification global warming’s “equally evil twin.” Ocean acidification threatens ocean life from coral reefs to plankton, Lubchenco said. In fact it may already be having serious impacts on marine life on the continental shelf. As oyster farmers have already learned, any marine species that relies on the alkaline forms of carbon to make a shell or for structural strength can be at risk.
Corrosive seawater can erode the shells of shellfish, or dissolve them altogether, as has been shown with the Whiskey Creek hatchery’s larval oysters. Hypoxia can stunt the growth of larval or juvenile shellfish just at that critical time when their shells are most vulnerable to the effects of acidification. Also, the Vibrio bacterium thrives in hypoxic conditions, said Robin Downey, executive director of the Pacific Coast Shellfish Growers Association.
In previous studies scientists found that acid sea water erodes the shells of tiny sea snails known as pteropods. In one experiment whole shells of the pteropod Clio pyramidata were collected from the subarctic Pacific Ocean and kept in corrosive sea water for 48 hours. The shells showed advanced dissolution on their leading edges, while no erosion was observed at the edges of C. pyramidata kept in non-corrosive sea water. Pteropods are an important food source for Pacific salmon, mackerel, herring, cod, and even whales. So if pteropods are adversely impacted by acidification, salmon could be too, said research team member Debby Ianson, quoted in a press release from NOAA. The loss of shellfish, particularly of water-filtering bivalves, could dramatically affect coastal water quality.
Reduced shell rubble means less habitat available for species that depend on using discarded shells for a portion of their life history. Free-swimming zooplankton may lose their ability to maintain protective shells. Since these species form the basis of many ocean food webs, their loss could be catastrophic. The survival of larval marine species, including commercial fish and shellfish, is likely to be reduced. The survival of adult shell-forming creatures might be less problematic—for example, clams and many other shell bearers live happily in estuarine mud, which is a highly-acidic environment.
Increased acidity also reduces the rate at which reef-building corals build their skeletons, and lowers the ability of corals to recover from bleaching and disease. According to NOAA, when the amount of atmospheric carbon reaches about 840 ppm, the oceans may no longer be able to maintain existing coral reefs. NOAA projects the atmosphere will reach that critical level by 2100.
The loss of coral reefs is likely to bring about further declines in commercial fisheries. Approximately half of all federally-managed fisheries depend on coral reefs and related habitats for some portion of their life cycles. The U.S. is the third largest seafood consumer in the world, with total consumer spending for fish and shellfish products approximately $60 billion per year, according to NOAA. Commercial fishing generates as much as $30 billion per year and accounts for nearly 70,000 jobs.
To better understand acidification and adapt to an increasingly acidified ocean, NOAA recommends increased monitoring of nearshore water chemistry, long-term satellite monitoring of coral reefs and ocean surfaces, expanded monitoring to predict changes in the ocean carbon cycle, improved technology to measure nearshore acidification, and better analysis of the social and economic impacts of acidification.
Hales said the study of ocean acidification is in its very early stages and presents plenty of opportunity for new research. “We’re in at the ground floor. If there is a silvery lining on this cloud, it’s that we may have a real opportunity to predict and respond to this issue.”
Richard A. Feely, Christopher L. Sabine, J. Martin Hernandez-Ayon, Debby Ianson, and Burke Hales. Evidence for Upwelling of Corrosive “Acidified” Water onto the Continental Shelf. Science 13 June 2008. 320: 1490-1492. First published online in Science Express, 22 May 2008. [DOI: 10.1126/science.1155676] (in Reports).
Ocean Acidification: State of the Science Fact Sheet. 2008. National Oceanic and Atmospheric Administration, US Dept. of Commerce. Washington, D.C.
PMEL Ocean Acidification Home Page. 2009 http://www.pmel.noaa.gov/co2/OA/. Accessed on the Web 20 July.
Northwest Association of Networked Ocean Observing Systems. http://www.nanoos.org/data/products/noaa_ocean_acidification/summary.php. Accessed on the Web 20 July.
Kolbert, Elizabeth. 2009. NOAA’s New Chief On Restoring Science To U.S. Climate Policy. Interview published in Yale Environment 360, http://www.e360.yale.edu/content/feature.msp?id=2169 9 July. Accessed on the Web 17 July.
Emergency Plan to Save Oyster Production on the West Coast. A Collaborative Proposal Prepared by the Pacific Coast Shellfish Growers Association, Whiskey Creek Hatchery, Taylor Hatchery, Pacific Shellfish Institute, Willapa-Grays Harbor Oyster Growers Association, Lummi Indian Tribe Hatchery, U.S. Department of Commerce (NOAA Aquaculture Program), Northwest Fisheries Science Center (NOAA), U.S. Department of Agriculture (ARS and CSREES), Oregon State University, AquaTechnics, Inc., and the Nature Conservancy. January 2009.
Burke Hales, Oregon State University College of Oceanic and Atmospheric Sciences. Carbon fluxes, hypoxia and ocean acidification: Lessons learned from carbon cycle studies of Oregon coastal waters. Public presentation given July 22, 2009 at Oregon Institute of Marine Biology, Charleston, Oregon.
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