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Can plankton adapt to warmer oceans?
14 February 2013
Issue 317
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weekly News Alert
Source: Thomas, M.K.,
Kremer, C.T., Klausmeier,
C.A., and Litchman, E.
(2012) A Global Pattern of
Thermal Adaptation in
Marine Phytoplankton.
Science. 338: 1085-1088.
DOI:
10.1126/science.1224836.
Contact:
[email protected]
Theme(s): Climate
Change and Energy,
Biodiversity, Marine
ecosystems
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SCU, The University of the
West of England, Bristol.
Future decades could see shifts in phytoplankton populations, leading to less
diversity among phytoplankton strains in increasingly warm tropical oceans,
researchers predict. These microorganisms play an important role in regulating the
Earth’s climate.
Phytoplankton carry out around half of all photosynthesis on Earth. They lower CO 2
concentrations in the oceans, add oxygen to our atmosphere, and are the basis of most
ocean and many freshwater food chains. When they die, phytoplankton also sequester
carbon in the deep ocean as they sink towards the ocean floor. The organisms’ close
relationship with CO2 and the carbon cycle means that climate change scientists need to
understand how global warming will alter phytoplankton populations. Additionally, ecologists
wish to understand phytoplankton to predict the oceans’ future health.
Water temperatures significantly affect the limits of phytoplankton growth rates: populations
near the equator have the potential to grow much faster than strains found in cooler waters,
near the poles, given sufficient nutrients. The researchers of this study believe that current
models underestimate the effects of rising temperatures on ocean ecosystems. Such models
focus on indirect mechanisms, such as how rising temperatures lead to fewer nutrients in
surface ocean waters. This study therefore investigated the direct effect of higher
temperatures on individual phytoplankton species.
The scientists used an eco-evolutionary model to investigate how strains of phytoplankton
adapt to current ocean temperatures. They also used species distribution models, to predict
how ocean temperature changes would affect populations. They analysed phytoplankton data
collected over 76 years by previous studies (published between 1935 and 2011), and also
used future temperature predictions generated by climate scientists. 194 strains of
phytoplankton belonging to over 130 species from the major groups were analysed.
The results suggest that by the end of the 21 st century, warmer oceans will lead to a greater
diversity of plankton populations nearer the poles, but fewer varieties in warmer, tropical
waters at the equator. Even though marine organisms can disperse over long distances
carried by ocean currents, each plankton strain grows best at an optimum temperature and
adapts to its local environment. Tropical strains appear to be most vulnerable to rising
temperatures. The researchers predict that around a third of current strains in the tropics
would become extinct by 2100 if mean temperatures increase by just 2°C. However, high
genetic diversity within species may prevent the loss of entire species.
Rising temperatures will thus affect phytoplankton in different ways, depending on their
location. Until we learn more about how phytoplankton evolve, there is significant
uncertainty regarding how these organisms will respond to climate change and to what
extent we can rely upon them to remove CO2 from our atmosphere. The future health of the
ocean ecosystems that depend on them is also threatened.