Climate change threatens calcifying plankton

Climate change is exerting increasing pressure on marine ecosystems, particularly affecting planktonic foraminifera, micro-organisms essential to the ocean carbon cycle. A recent study, conducted by the CEREGE research center in Aix-en-Provence, the Fondation pour la Recherche sur la Biodiversité (FRB) within the Centre de Synthèse et d'Analyse sur la Biodiversité (CESAB) in Montpellier, and the Max Planck Institute for Chemistry in Mainz (Germany), reveals that foraminifera populations are declining at an unprecedented rate due to ocean warming and acidification. High levels of CO₂, responsible for water acidification, are complicating the shell formation of these unicellular organisms, threatening their survival. These climate sentinels migrate to cooler waters in an attempt to adapt, but environmental changes are occurring faster than they can adjust.

A population of foraminifera in steep decline

The international team, made up of scientists from France, Germany, the Netherlands, Japan and Spain, analyzed nearly 200,000 samples of foraminifera collected since 1910 to study their response to climate change. The study, recently published in the journal Nature, shows that these species are migrating poleward, in search of warmer waters, at a rate of up to 10 kilometers per year. By examining vertical profiles, the researchers also found that some species are moving deeper into the ocean to escape warmer surface temperatures. Despite these movements, foraminifera populations have declined by 25% over the last 80 years. Tropical species are the hardest hit, as intense warming in these regions is probably disrupting their reproductive cycles, leading to a major decline.

Adaptation set to become increasingly difficult

Researchers estimate that by the end of the 21st century, many species of planktonic foraminifera could be faced with unprecedented environmental conditions, potentially exceeding their survival thresholds. This could lead to further extinctions in tropical regions, with consequent repercussions for marine ecosystems and carbon storage. Rising CO₂ levels in the ocean, limit the formation of calcium carbonate, an essential component for the construction of foraminifera shells. The reduced production of planktonic foraminifera shells could thus reduce the amount of carbon trapped on the seabed.

Key questions remain as to how these species will adapt to extreme acidification and rapidly changing environments. 

This research was funded by the Fondation pour la Recherche sur la Biodiversité (FRB) within the Centre de Synthèse et d'Analyse sur la Biodiversité (CESAB) and co-financed by the Max Planck Institute for Chemistry (MPIC) in Mainz, Germany, the CNRS-INSU LEFE program and the Aix Marseille Université - Amidex Initiative of Excellence.