Plankton changes radically according to latitude

The diversity and functions of the plankton species that inhabit the different oceans vary radically according to latitude, reveal the most recent analyzes made from the data collected during the French expedition Tara Oceans.

From 2009 and 2013, the sailboat Tara has traveled all the oceans of the globe. The objective of the biologists on board was to make a first mapping of planktonic species (bacteria, viruses, small animals drifting with the current) on a planetary scale.

First results have already described the variety of these planktonic organisms and their interactions in temperate and tropical regions.

The work published this week in the journal Cell incorporates new data from the schooner’s navigation around the North Pole.

Plankton 101

  • The word Planktos means “wanderer” in Greek;
  • they live in suspension or moves passively with the currents;
  • There is phytoplankton (plants) and zooplankton (animals);
  • It is at the base of the food chain of the aquatic ecosystem.

A great diversity

These recent analyzes are based on data collected from 189 sampling stations. They show that planktonic species are unevenly distributed on a planetary scale and that they are likely to adapt differently to the environmental conditions between the equator and the poles.

Our results clearly show that plankton diversity is greater around the equator and decreasing towards the poles.

Lucie Zinger, PSL University

These results could have important ecological, environmental and economic implications if ocean temperatures exceed a certain threshold.

In water as on land

“The patterns of biodiversity on earth, that of trees, animals, microbes, have been known for about 200 years, thanks to Alexander von Humboldt [naturalist and German explorer],” explains Chris Bowler, CNRS biologist and scientific coordinator of the mission Tara Oceans.

He observed that it [biodiversity] was rich in the tropics, and that it was declining towards the poles. 

Chris Bowler

“It remained to prove that this mechanism was also observed in the oceans, which are however very different, and where everything moves more dynamically than the ground,” explains the researcher.

Climate adaptation

This overriding influence of temperature on the distribution of plankton species raises questions about their ability to adapt to climate change, researchers say, recalling that they form the basis of the marine food chain, capture a significant share of dioxide of atmospheric carbon and emit oxygen by photosynthesis.

A parallel analysis of 47 million oceanic microbial genes has shown that microbial populations in warm waters have a vast genetic makeup that allows them to adapt their metabolism in case of change.

But the planktonic bacteria of the polar waters are more specifically adapted to their ecological niche than those of warm waters , and therefore less able to adapt their metabolism to oceanic warming .

These new data suggest that these bacteria may disappear to be replaced by new species from warmer waters.

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