the first time, NOAA and partner scientists have connected the concentration of
human-caused carbon dioxide in waters off the U.S. Pacific coast to the
dissolving of shells of microscopic marine sea snails called pteropods.
aboard NOAA Ship Fairweather sampled ocean waters and marine life to analyze
how they may be affected by ocean acidification during the 2013 West Coast
valuable fish such as salmon, sablefish and rock sole make the pteropod a major
part of their diet.
is the first time we’ve been able to tease out the percentage of human-caused
carbon dioxide from natural carbon dioxide along a large portion of the West Coast
and link it directly to pteropod shell dissolution,” said Richard Feely, a NOAA
senior scientist who led the research appearing in Estuarine, Coastal and Shelf
Science. “Our research shows that humans are increasing the acidification of
U.S. West Coast coastal waters, making it more difficult for marine species to
build strong shells.”
global ocean has soaked up one-third of human-caused CO2 emissions since the
start of the Industrial Era. While this reduces the amount of this greenhouse
gas in the atmosphere, it comes at a cost to the ocean. CO2 absorbed by
seawater increases its acidity, reducing carbonate ions, which are building
blocks used by shellfish to grow their shells.
pteropod, a sea snail the size of the head of a pin, is found in the Pacific
Ocean. It has been the focus of research in recent years because its shell is
affected by how much CO2 is in seawater and it may be an indicator of ocean
acidification affecting the larger marine ecosystem.
key piece of the new research was determining how much human CO2 emissions have
added to naturally occurring CO2 in seawater off the U.S. West Coast. Using
several decades of measurements from the Pacific Ocean taken through the U.S.
Global Ocean Carbon and Repeat Hydrography Program and new data from four NOAA
West Coast research cruises conducted between 2007 and 2013, the research team
developed a method to estimate additional CO2 from human-caused emissions since
the start of the Industrial Era as compared to CO2 from natural sources.
analysis shows that concentrations of human-caused CO2 are greatest in shallow
waters where the atmosphere gives up large amounts of its CO2 to the sea. The
researchers also estimated that CO2 concentrations from fossil fuel emissions
make up as much as 60 percent of the CO2 that enriches most West Coast
nearshore surface waters. But the concentrations dropped as they measured
deeper. It drops to 21 percent in deeper waters of 328 feet or 100 meters, and
falls even lower to about 18 percent in waters below 656 feet or 200 meters.
Concentrations vary depending on location and seasons as well.
researchers created a detailed map of the human-generated CO2 concentrations,
they looked at how pteropod shells fared in areas with varying seawater CO2 concentrations.
They found more than 50 percent of pteropod shells collected from coastal
waters with the high CO2 concentrations were severely dissolved. An estimated
10 to 35 percent of pteropods taken from offshore waters showed shell damage
when examined under a scanning electron microscope.
estimate that since pre-industrial times, pteropod shell dissolution has
increased 20 to 25 percent on average in waters along the U.S. West Coast,”
said Nina Bednaršek of the University of Washington. Earlier research by
Bednaršek and others has shown that shell dissolution affects pteropod swimming
ability and may hamper their ability to protect themselves from predators.
new research suggests we need a better understanding of how changes in
pteropods may be affecting other species in the food chain, especially
commercially valuable species such as salmon, sablefish, and rock sole that
feed on pteropods,” Bednaršek added.