Purple sea urchin (Photo: Shane Anderson)

On a global basis, ocean acidity has increased about 30 percent since the start of the Industrial Revolution. So what, you might ask? The problem lies in basic chemistry: carbon dioxide (CO2) in the air mixes into seawater and, through a series of reactions, weakens calcium carbonate structures such as shells and coral reefs. In addition, recent studies suggest that increasing acidity (carbon dioxide forms carbonic acid in water) interferes with the ability of corals, sea urchins and other creatures to regulate functions from metabolism to reproduction.

Not all parts of the ocean are equally vulnerable, says Chan, an assistant professor of zoology. “Some places are going to be pretty resilient. They won’t feel the effects (of increasing acidity) for many decades or even a couple of hundred years. But there are other areas where people have said we really need to pay attention, that will be early warning systems, the canary in the coal mine.”

Two Sides of the Same Coin

The West Coast is one of those areas, and what makes it so vulnerable, says Chan, is the cold, deep water that swimmers in Oregon encounter during the summer. As north winds push warmer surface water away from the shoreline and out to sea, cold water comes up from offshore to replace it. This water tends to be more acidic and lower in oxygen than surface water, and as if adding insult to injury, it is loaded with nutrients that, under the right conditions, feed massive plankton blooms and set the stage for the so-called “dead zone” that has occurred regularly off Oregon since 2002.

Scientists define a dead zone as water with little oxygen, less than two parts per million to be precise (a condition known as “hypoxia”). As microbes chew away on dead plankton, they drop oxygen levels further still. “Hypoxia and acidification are opposite sides of the same coin,” says Chan. The microbes that feed on plankton blooms also release carbon-dioxide and make the water more acidic.

Since April 2009, Chan and colleagues in the Partnership for Interdisciplinary Studies of Coastal Oceans, or PISCO, have been measuring just how acidic this water gets. From a station just offshore of Strawberry Hill State Park, (“a long fly ball from the surf zone,” says Chan) to about 20 miles out, they have placed sensors that record CO2 (actually, pCO2, or the partial pressure of CO2 in the water, a measure of its concentration) and pH. They have found that upwelling water can contain from 150 to 1,450 microatmospheres, reaching levels nearly four times the global average. At the same time, pH levels can drop as low as 7.5. Such corrosive conditions can last for up to five months during the summer and fall.

Limits to Growth

Through PISCO, scientists are working to understand how sea urchins and mussels are responding to these variable conditions and how they might adapt in a warmer, more acidic future. “They already may be close to their acclimatization or adaptational capacity,” says Bruce Menge, OSU distinguished professor of zoology and lead scientist on the project, “and thus may have limited ability to respond to additional increases in CO2.”

Monitoring the West Coast’s pH “climate” is a high priority. To complement the Oregon data from Strawberry Point, scientists will establish stations off Southern and Northern California. In addition, researchers at UC Santa Barbara and the UC Davis Bodega Marine Lab will raise sea urchins and mussels in laboratory tanks, expose both larvae and adults to increasing CO2 and analyze differences in gene function. By using multiple sites, the project will evaluate the likely future for urchins and mussels across a wide range of ocean conditions.

“Here are organisms that we’ve studied for decades,” says Chan, “and we know the important roles they have in structuring the communities we see out there. We know they’re important players in the coastal ecosystem.”
“For the first time,” adds Menge, “we will be able to examine the genetics and ecology of these key organisms to see how populations that span over a thousand miles of coastline are coping with changes in ocean chemistry.”

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Learn how PISCO is taking a collaborative approach to the science of ocean acidification.

In Shellfish on Acid, learn how OSU researchers are working with the Whiskey Creek Shellfish Hatchery to understand the effects of acidification on oysters, clams and mussels.

For information about supporting research and teaching through faculty endowments, contact the Oregon State University Foundation, 1-800-354-7281 or visit CampaignforOSU.org.

Burke Hales, OSU College of Oceanic and Atmospheric Sciences (Photo: Don Frank)

Water that upwells seasonally along the West Coast of North America is growing increasingly acidic, according to a survey conducted in 2007 by an international team of scientists. In June, they reported finding acidified ocean water within 20 miles of the shoreline, raising concern for marine ecosystems from Canada to Mexico.

Deep-ocean currents take years to transport acidified water to upwelling regions, say members of the research team, which included Burke Hales, an associate professor in the College of Oceanic and Atmospheric Sciences at Oregon State University. Thus it is likely that increasingly acidic water will continue to upwell along the West Coast in the future, they add.

“The coastal ocean acidification train has left the station, and there not much we can do to derail it,” says Hales, an author of a report published in Science. The research was funded by the National Oceanic and Atmospheric Administration (NOAA) and the National Aeronautics and Space Administration (NASA).

In their survey, the researchers used the Wecoma, an OSU research vessel owned by the National Science Foundation, to collect water samples at pre-determined points off shore. They found indications that acidified water in upwelling regions had previously been at the ocean surface about 50 years ago. At that time, atmospheric CO₂ levels were roughly 310 parts per million.

Since then, CO₂ levels have risen in the atmosphere by about 20 percent. When it reacts with water, CO₂ generates carbonic acid, which, at high enough concentrations, can harm shell-building organisms such as corals, clams, snails and oysters. Scientists call such water “corrosive” because it can weaken shells and coral reefs.

The study was the first in a planned series of biennial observations of the carbon cycle along the West Coast. In addition to Hales, principal investigators included Richard A. Feely and Christopher Sabine of the NOAA Pacific Marine Environmental Laboratory; J. Martin Hernandez-Ayon, the University of Baja California in Mexico; and Debby Ianson, of Fisheries and Oceans Canada, Sidney, B.C.

Shells at Risk

Pink scallop (Illustration courtesy of Oregon Sea Grant)

“When the upwelled water was last at the surface, it was exposed to an atmosphere with much lower CO₂ levels than today’s,” Hales points out. “The water that will upwell off the coast in future years already is making its undersea trek toward us, with ever-increasing levels of carbon dioxide and acidity.”

Scientists have become increasingly concerned about ocean acidification in recent years, as the world’s oceans absorb growing levels of carbon dioxide from the atmosphere. Carbonic acid has a corrosive effect on aragonite, the calcium carbonate mineral that forms the shells of many marine creatures.

Certain species of phytoplankton and zooplankton, which are critical to the marine food web, may also be susceptible, the scientists point out, although other species of open-ocean phytoplankton have calcite shells that are not as sensitive.

“There is much research that needs to be done about the biological implications of ocean acidification,” Hales says. “We now have a fairly good idea of how the chemistry works.”

Atmospheric CO₂ levels form the beginning baseline for carbon levels in ocean water. As water sinks away from the surface and moves toward upwelling areas, CO₂ levels also rise from the normal process of respiration by plants and animals. As that nutrient-rich water is upwelled, it triggers additional phytoplankton blooms that continue the process.

Dead Zones and Acidification

There is a strong correlation between recent hypoxia events off the Northwest coast and increasing acidification, Hales says.

“The hypoxia is caused by persistent upwelling that produces an over-abundance of phytoplankton. When the system works, the upwelling winds subside for a day or two every couple of weeks in what we call a ‘relaxation event’ that allows that buildup of decomposing organic matter to be washed out to the deep ocean.

Razor clam (Illustration courtesy of Oregon Sea Grant)

“But in recent years, especially in 2002 and 2006, there were few if any of these relaxation breaks in the upwelling, and the phytoplankton blooms were enormous,” Hales adds. “This decomposition puts more CO₂ into the system and increases the acidification.”

The researchers found that the 50-year-old upwelled water had CO₂ levels of 900 to 1,000 parts per million, making it “right on the edge of solubility” for calcium carbonate-shelled aragonites, Hales says.

“If we’re right on the edge now based on a starting point of 310 parts per million, we may have to assume that CO₂ levels will gradually increase through the next half century as the water that originally was exposed to increasing levels of atmospheric carbon dioxide is cycled through the system. Whether those elevated levels of carbon dioxide tip the scale for aragonites remains to be seen.

“But if we somehow got our atmospheric CO₂ level to immediately quit increasing,” Hales adds, “we’d still have increasingly acidified ocean water to contend with over the next 50 years.”

Variation is the Rule

Mussel (Illustration courtesy of Oregon Sea Grant)

Hales says it is too early to predict the biological response to increasing ocean acidification. There is already a huge seasonal variation in ocean acidity based on phytoplankton blooms, upwelling patterns, water movement and natural terrain. Upwelled water can be pushed all the way onto shore, he says, and barnacles, clams and other aragonites have likely already been exposed to corrosive waters for a period of time.

They may be adapting, or they may already be suffering consequences that scientists have not yet determined.

“You can’t just splash some acid on a clamshell and replicate the range of conditions the Pacific Ocean presents,” Hales says. “This points out the need for cross-disciplinary research. Luckily, we have a fantastic laboratory right off the central Oregon coast that will allow us to look at the implications of ocean acidification.”

• Burke Hales’s Web page
• College of Oceanic and Atmospheric Sciences
• NOAA Press release
• Journal article in Science
• The National Oceanic and Atmospheric Administration
• The National Aeronautics and Space Administration
• National Science Foundation