Paris (AFP)
With global warming, northern hemisphere plankton tend to migrate farther north, according to a study published Wednesday in the journal Nature and dedicated to these microorganisms at the base of the ocean food chain.
"This is not good news for marine ecosystems," says Lukas Jonkers, lead author and researcher at the University of Bremen.
"We have pushed marine ecosystems, or at least this group of zooplankton, far from their natural state, and that is very worrisome: it means that even if we manage to keep warming below 1.5 ° C, Doubtful, the world's ecosystems are likely to be deeply affected. "
The team studied the case of planktonic foraminifera, unicellular microorganisms with a rigid and resistant envelope. An envelope that falls to the bottom of the water at their death, and allows scientists to keep for centuries the trace of these populations in various parts of the world.
The researchers compared recent samples (1978-2013) with others from ocean sediments dating back several centuries.
Appraisal: recent samples similar to ancient ones collected in seas further south, suggesting that plankton migrated northward as the water gained temperature.
"Everything has moved north," says Jonkers for AFP. "At this place you always find many different species, but now we see that this set consists of species preferring warmer waters".
For example, the species found today near Greenland evolved further south, judging by sediments dating from the pre-industrial era and collected further south.
In total nearly 4,000 samples were analyzed from various areas of the northern hemisphere. The situation in the southern hemisphere is not analyzed by this study, but for Lukas Jonkers, the pattern is similar.
"Where temperatures have changed the most, species have changed the most," he says, evoking a rather gradual pace of change.
According to him, nothing has shown at this stage of extinction of species.
However, questions of survival could arise for plankton as for the fauna resting on this food, if they do not adapt quickly enough to survive and cohabit with others in their new environment.
This study adds to others that show the impact of warming on the ocean and its people. So in the Arctic, seals and whales are already forced to change their eating habits, showed work published in March.
? 2019 AFP