SEATTLE – Scientists years ago figured out that a group of tiny snail-like sea creatures crucial to marine food webs may one day be an early victim of changing ocean chemistry.
Researchers predicted that pteropods, shelled animals known as sea butterflies, could begin dissolving by 2038 as human-caused carbon-dioxide emissions begin souring the seas in a process known as ocean acidification.
But new research by Seattle scientists concludes that corrosive seas are damaging pteropods right now – decades earlier than expected. And that damage was recorded in the south Atlantic Ocean, where surface pH doesn’t dip as low as it has off the Washington coast or in Puget Sound.
The finding suggests that changing sea chemistry already could be harming pteropods in the Northwest, with potentially vast implications for the marine food chain.
And it comes as a panel of experts organized by Washington Gov. Chris Gregoire last week unveiled recommendations for ways Washington can attempt to combat changes to ocean chemistry. The panel recommended 42 wide-ranging actions. It cited 18 priorities, ranging from finding innovative techniques such as seaweed farming to capture and remove carbon to reducing greenhouse gas emissions.
“This is really an important discovery because here in the Northwest, our pink salmon, for example, are dependent on pteropods for survival in the open ocean in their first year of life,” said Richard Feely, a scientist with the National Oceanic and Atmospheric Administration in Seattle. Feely, an acidification expert, participated in the research. “More than 50 percent of their diets are these pteropods.”
The first victims
Scientists have long known that greenhouse-gas emissions from the burning of fossil fuels were being taken up by the seas and slowly changing ocean chemistry, but research in recent years shows those changes are coming far faster than initially expected. As a result, scientists in laboratories around the world have been scrambling to figure out how those changes will affect marine life.
This lab work has shown that increasing carbon dioxide in the oceans eventually could kill, endanger or alter the behavior of many marine organisms, from crab and squid to clownfish and clams. The most sensitive species are those that rely on calcium carbonate to form shells or other body parts, such as the inner parts of many fish ears. Significant changes to important species are expected to ripple though the food chain.
This latest research, published Nov. 25 in the journal Nature Geoscience, is different. It places pteropods, which are eaten by many fish, among a mere handful of marine species worldwide being impacted right now. The others are Pacific oysters along the Northwest coast and tropical corals in the South Pacific.
“It was a surprise to me to see that level of damage in a wild field population,” said Dave Mackas, a scientist with Canada’s Department of Fisheries and Oceans who has studied pteropods in the Northwest. “I think we should take it as another warning signal.”
A vital role
Like corals, pteropods are central to many ocean ecosystems. They’re not much bigger than pepper grains, but they eat plankton and occur in great clusters that are easily scooped up by fish.
“They’re a great example of some tiny, not-charismatic creature that is incredibly important,” said Gretchen Hofmann, a University of California at Santa Barbara biologist and ocean-acidification expert. “They’re small, but carry an enormous amount of nutrition and are eaten even by very big fish. If you’re in the Antarctic and see a beautiful emperor penguin, it exists by eating fish under the sea ice. And those fish eat pteropods.”
The new discovery was made by an international team of researchers led by Nina Bednarsek, who was affiliated with the British Antarctic Survey. She since has been hired by NOAA in Seattle.
During a 2008 research cruise south and east of the Falkland Islands off the tip of South America, Bednarsek gathered samples of Limacina helicina antarctica, a southern Atlantic species of pteropod. Some of the samples came from an area where cold deep water wells up from below, much as it does off the Washington coast.
“We brought the samples back home and saw these really tiny changes on the shell,” Bednarsek said.
Pteropods create extremely thin shells that are highly susceptible to chemical changes in seawater. Using a complex set of tests, Bednarsek discovered the shells were dissolving.
While the damage wasn’t enough to kill the animals, it weakened them, making them more vulnerable to predators and infection. And, as scientists before her had predicted through lab work, the degree of dissolution worsened in creatures taken from waters containing more carbon dioxide.
Search for the cause
The discovery prompted a big question: “When we established that we had dissolution, we wondered, ‘What’s driving this?’ ” Bednarsek asked.
As it turns out the answer, in part, is: humans.
Because deep frigid water normally holds more carbon dioxide, its pH is naturally lower than that of surface waters. South Atlantic waters, naturally, would dissolve pteropods if they lived at depths below 1,000 meters.
But these creatures were being dissolved in some cases just 200 meters below the sea surface – up where pteropods actually live.
That deep water has always welled up from below, but the addition of carbon dioxide from fossil fuels had pushed it past the threshold that pteropods can withstand.
“The deep water coming up just keeps getting more and more acidic,” said Hofmann.
The researchers only saw particularly serious damage in one spot, which left other questions unanswered.
“Was that a worse-case event that happened to hit that site?” asked Mackas, the Canadian scientist. “Or is it common or persistent there? I’m sure someone is looking at that right now.”
It’s too soon to fully grasp the implications of Bednarsek’s work, especially in the Pacific Northwest.