Researchers say ocean changes could limit plankton growth in the tropics
By Summit Voice
SUMMIT COUNTY — Warming ocean temperatures during the coming decades could result in a significant shift in the distribution of phytoplankton, with as-yet unknown consequences for global climate, according to researchers with Michigan State University.
Starting with what they do know, the scientists said warmer oceans will cause populations of these marine microorganisms to thrive near the poles and shrink in equatorial waters.
“In the tropical oceans, we are predicting a 40 percent drop in potential diversity, the number of strains of phytoplankton,” said MSU biologist Mridul Thomas.
“If the oceans continue to warm as predicted, there will be a sharp decline in the diversity of phytoplankton in tropical waters and a poleward shift in species’ thermal niche — if they don’t adapt,” Thomas said. Phytoplankton and Earth’s climate are inextricably intertwined. The microorganisms use light, carbon dioxide and nutrients to grow. Although phytoplankton are small, they flourish in every ocean, consuming about half of the carbon dioxide emitted into the atmosphere.
When they die, some sink to the ocean bottom, depositing their carbon in the sediment, where it can be trapped for long periods of time.
Phytoplankton in warmer equatorial waters grow much faster than their cold-water cousins. With worldwide temperatures predicted to increase over the next century, it’s important to gauge the reactions of phytoplankton species, say the scientists.
“The research is an important contribution to predicting plankton productivity and community structure in the oceans of the future,” said David Garrison, program director in the National Science Foundation’s Division of Ocean Sciences, which funded the research along with NSF’s Division of Environmental Biology. “The work addresses how phytoplankton species are affected by a changing environmentand the really difficult question of whether adaptation to these changes is possible,” Garrison said.
“These results will allow scientists to make predictions about how global warming will shift phytoplankton species distribution and diversity in the oceans,” said Alan Tessier, program director in NSF’s Division of Environmental Biology. “They illustrate the value of combining ecology and evolution in predicting species’ responses.”
The research shows that phytoplankton have adapted to local temperatures, but based on projections of ocean temperatures in the future, many phytoplankton may not adapt quickly enough.
Since they can’t regulate their temperatures or migrate, if they don’t adapt, they could be hard hit, said MSU’s Colin Kremer.
“We’ve shown that a critical group of the world’s organisms has evolved to do well under the temperatures to which they’re accustomed,” Kremer said.
“Future models that incorporate genetic variability within species will allow us to determine whether particular species can adapt, or whether they will face extinction,” said Christopher Klausmeier, also of MSU.
The research was reported in this week’s online journal Science Express.