The population of a microscopic marine alga in the north Atlantic Ocean apparently is booming due to climate change, but scientists - who've been caught off-guard by the development - aren't sure what it means for the aquatic environment.
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The abundance of single-celled aquatic organisms called coccolithophores increased by a factor of 10 since 1965 and 2010, with a particularly huge spike since the late 1990s, according to a study just published in the journal Science. That increase shocked scientists, some of whom had predicted that the alga might actually decline, due to increasing acidity of the water in which it lives.
"Something strange is happening here, and it's happening much more quickly than we thought it should," Anand Gnanadesikan, associate professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at Johns Hopkins University and one of the study's co-authors, said in a release.
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The coccolithophore surge might be good news for some of the creatures who consume them, such as smaller fish and zooplankton - or not, because it could be a sign that climate change is affecting marine ecosystems more drastically than scientists had believed.
"What is worrisome is that our result points out how little we know about how complex ecosystems function," Ghanadesikan said.
Researchers' statistical analysis of data from the Continuous Plankton Recorder survey, which was collected in the North Atlantic and the North Sea over the past half-century, points to rising CO2 in the ocean as the cause of the population spike.
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Some scientists expected that rising ocean acidity from the extra CO2 that's being absorbed would be harmful to the coccolithophores. But study co-author Wlliam M. Balch, a marine scientist at the Bigelow Laboratory for Ocean Sciences in Maine, said their increasing abundance also is consistent with natural history.
"Coccolithophores have been typically more abundant during Earth's warm interglacial and high CO2 periods," said Balch, an expert on coccolithophores. "The results presented here are consistent with this and may portend, like the ‘canary in the coal mine,' where we are headed climatologically."
It's also unclear what effect the abundance of coccolithophores will have on the oceans' ability to store carbon, which serves as a major brake on climate change. The creatures cloak themselves in a distinctive cluster of pale disks made of calcium carbonate, or chalk, and for every ton of them produced, 320 pounds of carbon is taken out of circulation.
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When the creatures die, their bodies sink harmlessly to the ocean bottom and become part of the sediment, keeping the carbon from rising to the surface. That makes them a long-term positive factor in the fight against global warming.
Over the short term, though, the coccolithophore population explosion could have a detrimental effect, because they release carbon dioxide as they form their plates of calcium carbonate, which are called coccoliths. Those immediate emissions add to the greenhouse effect in the atmosphere, and there is concern that the increase in the creatures' number could cause those emissions to spike.