What's fueling the rise of coccolithophores in the oceans?

Rising carbon dioxide in the ocean is causing a spike in population of microscopic marine alga, says a new study.  

Karl Bruun/Nostoca Algae Laborator/Nikon Small World/AP/File
This undated handout image provided by Karl Bruun, Nostoca Algae Laboratory, photo courtesy of Nikon Small World, shows a number of marine diatom cells (Rhizosolenia setigera), which are an important group of phytoplankton in the oceans. Much of life on Earth depends on tiny plant plankton. They are the foundation of the bountiful ocean food web, make half the world's oxygen and suck up harmful carbon dioxide. A new study published Monday in the journal Nature Climate Change demonstrates that ocean acidification could dramatically impact the world's plankton.

Phytoplankton, micro-organisms that float, as opposed to swim, are rapidly thriving in the North Atlantic, suggesting an environmental shift that defies previous scientific predictions.

Scientists have long thought that the number of plankton species would decline due to increased acidity in the oceans. However, over the last four decades or so they have grown to be much more in abundance, a new study indicates.

The study, led researchers from Johns Hopkins University, shows a ten-fold increase in the number of coccolithophores, single-celled algae with a limestone shell, that are found throughout the planet's oceans between 1965 and 2010, and a particularly sharp spike since the late 1990s.

"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, and also one of the study's five authors said, in a news release.  

During their study, the team, analyzed Continuous Plankton Recorder survey data from the North Atlantic Ocean and North Sea since the mid-1960s. This revealed that higher carbon dioxide levels in our planet’s oceans may be causing an increase in the population of coccolithophores.

"Our statistical analyses on field data from the CPR point to carbon dioxide as the best predictor of the increase in coccolithophores,” Sara Rivero-Calle, a Johns Hopkins doctoral student and lead author of the study said. "The consequences of releasing tons of CO2 over the years are already here and this is just the tip of the iceberg."

According to William M. Balch of the Bigelow Laboratory for Ocean Sciences in Maine, a co-author of the study, scientisits have long expected that increasing ocean acidification acidity due to higher carbon dioxide would suppress these chalk-shelled organisms. The new study shows, it didn't.

"Coccolithophores have been typically more abundant during Earth's warm interglacial and high CO2 periods," said Balch. "The results presented here are consistent with this and may portend, like the 'canary in the coal mine,' where we are headed climatologically."

A study last summer projected that the balance of various plankton species will radically change as the world’s oceans increase in acidity over the next 85 years. The Christian Science Monitor reported, “By 2100, ocean acidification will have grown to such an extent that some species of phytoplankton ‘will die out, while others will flourish’”.

According to the researchers of the latest study, the report sheds light on the effects of increasing carbon to marine life.

"These clearly represent major shifts in ecosystem type," Gnanadesikan said. "But unless we understand what drives coccolithophore abundance, we can't understand what is driving such shifts. Is it carbon dioxide?"

Gnanadesikan notes that while the report is certainly is good news for creatures that eat coccolithophores, it is not clear whether the rapid growth in the tiny plankton's population is harmful or beneficial to the planet.

"What is worrisome," he said, "is that our result points out how little we know about how complex ecosystems function." 

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