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Warming Boosts Phytoplankton Productivity & Diversity

Rising temperatures benefit phytoplankton, increasing photosynthesis and biodiversity of these primary producers, according to a new study conducted by scientists from the University of Exeter and Queen Mary University of London (QMUL).

Phytoplankton are microscopic single-celled plants that are found in both freshwater and marine ecosystems around the world. Yet, despite their tiny size, they absorb the equivalent amount of carbon dioxide as the world's tropical rainforests, and thus play a significant role in carbon sequestration. It is therefore important that we understand how these organisms respond to climate warming.

The results of this study, which was conducted over a five year period in ponds that were artificially warmed to simulate the rise in temperatures anticipated towards the end of this century, were recently published in the scientific journal PLOS Biology.

The scientists discovered that phytoplankton residing in ponds where temperature increased by 4 degrees had a more diverse species richness (they consisted of 70% more phytoplankton species), and phytoplankton in these ponds had a higher rate of photosynthesis, which in turn enables them to remove even more atmospheric CO2.

The researchers examined the phytoplankton cells under a microscope, identifying the species, as well as counting and measuring them. The rate of photosynthesis and/or respiration was determined by measuring the consumption (photosynthesis) and production (respiration) of oxygen respectively.

The study revealed that phytoplankton in warmer ponds showed the following characteristics:

  • They had a greater species richness
  • Species abundance was more consistent
  • They had a greater biomass
  • The phytoplankton community consisted dominantly of larger species

Compared to previous studies conducted on a smaller scale in laboratory experiments over a shorter time-frame, the results of this new study show that projected climate warming could in fact result in an increase in phytoplankton biodiversity as well as photosynthesis in certain regions. However, the researchers point out that their results can't be extrapolated on a global scale because other areas may see declines due to different ecological factors at play.

The researchers acknowledge that their findings can be largely attributed to the fact that their study was conducted in outdoor ponds — effectively open ecosystems that facilitated immigration from the surrounding environment to replace any species lost in the process.

According to lead author, Dr. Gabriel Yvon-Durocher from the Environment and Sustainability Institute at the University of Exeter, the increases observed in phytoplankton biodiversity seem to be a consequence of the effect that warming has on zooplankton — the tiny organisms that feed on phytoplankton.

"Higher grazing rates by the zooplankton, which prefer small abundant phytoplankton species, prevent the ecosystem being dominated by just a few of these highly competitive species, allowing species which are inferior competitors for resources to coexist," Yvon-Durocher explains. "What our study clearly shows is that future global warming is likely to have a major impact on the composition, biodiversity and functioning of plankton, which play a pivotal role in aquatic ecosystems."

References & Further Reading

Five Years of Experimental Warming Increases the Biodiversity and Productivity of Phytoplankton.
Gabriel Yvon-Durocher, Andrew P. Allen, Maria Cellamare, Matteo Dossena, Kevin J. Gaston, Maria Leitao, José M. Montoya, Daniel C. Reuman, Guy Woodward, Mark Trimmer. PLOS Biology, 2015;
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