Sea snails showing signs of global warming wear and tear

Study helps quantify ocean acidification impacts

snails
Scientists estimate that pteropod shell dissolution has increased 20 to 25 percent on average in waters along the U.S. West Coast due to CO2 emitted by humans.

Staff Report

By mapping CO2 emissions and comparing that information with data on CO levels in the ocean, scientists say they can now show to what degree the build-up of heat-trapping pollution contributes to the dissolving of shells of microscopic marine sea snails called pteropods.

Other studies from the Southern Hemisphere have reached similar conclusions. Pteropods are an important food for commercially valuable fish species like salmon, sablefish and rock sole.

“This 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.

“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.” The findings appear in the journal Estuarine, Coastal and Shelf Science.

Oceans have absorbed about a thirnd of human-caused CO2 emissions since the start of the industrial era. The CO2 is making oceans more acidic, reducing the amount of carbonate ions that shellfish use a building blocks for their shells. Pteropods, about the size of the head of a pin, may be indicators of how ocean acidification affects ecosystems.

 To make their findings, the scientists first had to figure out how human CO2  emissions have added to naturally occurring CO2 in seawater off the U.S. West Coast. The answers came from several decades of measurements in the Pacific 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 analysis showed 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.

As 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.

“We 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.
“This 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.
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