Acidification threatens oceans

BY PAULA DEL GIUDICE
Most of the news surrounding too much carbon dioxide in the atmosphere is aimed at our changing climate. But there’s another issue when it comes to carbon in the atmosphere that threatens to harm the oceans and disrupt the food chain. It’s ocean acidification.
The oceans cover 71 percent of the Earth’s surface. They act as huge “sinks” for carbon dioxide, but when carbon dioxide is absorbed by seawater, chemical reactions occur that reduce the potential for hydrogen, carbonate ion concentration and the saturation state of biologically important calcium carbonate minerals which are essential for forming shells and bones for many ocean organisms. This is ocean acidification.
Our oceans are 30 percent more acidic since the Industrial Revolution began. If trends continue, by the end of this century our oceans will be 100-150 percent more acidic, according to the National Oceanic and Atmospheric Administration.
That will create a chemical imbalance the oceans haven’t experienced in 20 million years.
Some plants in the ocean, such as algae and seagrasses, can make use of that extra carbon dioxide to accomplish photosynthesis, similar to plants on land.
However, the dramatic effect increasing acidity can have on calcifying organisms, such as oysters, clams, sea urchins, corals, calcareous plankton and pteropods is devastating.
Pteropods are tiny mollusks that are eaten by a wide variety of ocean creatures from krill to whales. They are a major source of food for Pacific salmon. When placed in ocean water with the predicted acidity for the year 2100, their shells dissolve after 45 days. According to Richard Feely, a senior scientist with NOAA’s Pacific Marine Environmental Laboratory a 10 percent decrease in pteropod production leads to a 20 percent drop in mature salmon body weight.
No one knows the evolving situation of ocean acidification better than Bill Dewey, director of public affairs for Taylor Shellfish Farms in Shelton, Washington. In 2006, oyster seed hatcheries on the West Coast began experiencing massive die-offs of their stock.
In 2009, Taylor Shellfish had a major die-off of the wild oyster larvae in its facility. Down in Netarts, Oregon, a major die-off occurred at the Whiskey Creek Hatchery the previous year. It was at first, attributed to larvae-eating bacterium called Vibrio tubiashii raging through their tanks, but the die-offs continued, even when Vibrio tubiashii wasn’t present any longer.
The shellfish industry is responsible for a combined $110 million of income to the states of California, Oregon and Washington. In some places, shellfish aquaculture is the No. 1 employer.
Oyster farmers throughout the country depend on seed stocks from hatcheries to begin their growing cycle. With this massive die-off, not only were seed farmers and their businesses devastated, but so were the hundreds of farms they supply. While this was happening scientists noticed that the water entering the hatcheries was more acidic than normal. A strong ocean upwelling was the culprit.
Upwelling is when more carbon dioxide fills the air and it is absorbed by phytoplankton on the surface.
As those phytoplankton die and begin to decompose, they release carbon dioxide into the water column. This is when the carbonic acid develops. Cold water can hold more carbon dioxide so it sinks to the bottom of the ocean. It might not be so bad if the carbon dioxide-filled water remained at the bottom of the ocean, but it doesn’t. Particularly along the West Coast it rolls back to the surface. The water that wells up from the bottom of the ocean today was actually absorbed about 30 to 50 years ago, when increased industrialization began pushing more carbon dioxide into the atmosphere. Just think about what will happen in 30 to 50 years from now since we’ve pushed past 400 parts of carbon dioxide per million in the atmosphere.
In 2007, Feely and an international team of scientists conducted the first large-scale carbon dioxide survey of waters along the West Coast from Canada to Mexico. Their work showed what occurs when the winds blow from the north causing the upwelling of cold, carbon dioxide-laden waters to reach very near the shore.
Those studies allowed hatchery managers, who operate in controlled environments, to experiment with adaptive management strategies.
At Taylor Shellfish, when they see the weather shifting to more northerly winds, staff hurries to fill their tanks and then shut off the intake. They know they have about 24 hours before the upwelling brings acidic waters through their intake pipes.
They also wait to fill the tanks until the afternoon when the phytoplankton and eel grasses have had a chance to complete photosynthesis, pulling some of the carbon out of the water. Taylor Shellfish is experimenting with growing seagrass refuges near the hatchery to pull additional carbon out of the water.
The company also injects calcium carbonate into the hatchery water system to assist in reducing the acidity. Some of the seed production has been shifted to Hawaii where production is easier during the winter and waters are not impacted by upwelling.
While adaptive management strategies can assist the production of shellfish in controlled situations short-term, they do little to address the long-term health of our oceans.
“Ocean acidification is a big deal,” Dewey said. “Sea water chemistry is going to change in dramatic ways in our lifetime. We are going to watch all the organisms shift in the ocean in ways we can’t fully understand.” ♦
— Circle of Chiefs articles are written by those who have received the Circle of Chiefs Award for conservation reporting and coverage. The Circle of Chiefs are considered OWAA’s conservation council. The article reflects the opinion of the author. If you’d like to add to the discussion, please send a letter to the editor.
— Paula J. Del Giudice is the executive director of the nonprofit Pacific Northwest Pollution Prevention Resource Center. Her articles have appeared On GreenBiz.com. She has been a member of OWAA since 1980 and is a member of OWAA’s Circle of Chiefs.