Climate Change Threatens Key Ocean Plankton Groups

Ocean warming and acidification disrupt marine ecosystems

Planktonic foraminifera are tiny marine organisms, which are essential to the ocean's carbon cycle. A recent study conducted by the CEREGE research center in Aix-en-Provence,  Aix-Marseille University, the Center for the Synthesis and Analysis of Biodiversity (CESAB) in Montpellier, and the Max Planck Institute for Chemistry in Mainz, reveals that these populations are shrinking at an alarming rate due to ocean warming and acidification. Elevated CO₂ levels and thus acidifying waters are making it harder for these single-cell organisms to form their shells, putting their survival at risk. Some foraminifera have begun migrating to cooler waters in an attempt to adapt, but environmental changes are occurring faster than they can keep up with.

According to a recent study published in Nature, many planktonic foraminifera species may face unprecedented environmental conditions by the end of this century, potentially surpassing their survival thresholds. Planktonic foraminifera are single-celled organisms living in seawater, many of which carry a calcium carbonate shell. In tropical regions, the changing environmental conditions could trigger further extinctions, impacting marine ecosystems and the ocean's carbon storage capacity.
An international team involving scientists from France, Germany, the Netherlands, Japan, and Spain analyzed nearly 200,000 datasets since 1910 to examine their response of planktic foraminifers to climate change.

The research shows that many species are migrating poleward towards cooler waters, at rates up to 10 kilometers per year. The data also reveal that some species have migrated deeper into the ocean to escape the rising surface temperatures. Despite these shifts, foraminifera populations have declined by 25 % over the past 80 years. Tropical species experienced the biggest losses because the intense warming in these regions disrupts their reproductive cycles. The rising CO₂ levels and ocean acidification also reduce the formation of calcium carbonate (CaCO₃) from which foraminifera build their shells. Since the empty shells of deceased plankton sink to the seafloor, less carbon is stored when shell production decreases.

Sonia Chaabane, the study's lead author and researcher at CEREGE and the Max Planck Institute for Chemistry, emphasized the implications of the findings: "Our data show that planktonic foraminifera, which play a crucial role in the ocean’s carbon cycle, are struggling to survive in a rapidly changing climate. These organisms are like sentinels, warning us of the drastic effects that warming and acidification have on marine ecosystems." Complex interactions between climate and ecosystems are likely to be better understood as a whole through bioindicators like foraminifera rather than through individual measurements. “In view of advancing climate change, researchers are faced with the question of adaptation strategies individual species of planktonic foraminifera will develop in the near future” says Ralf Schiebel from the Max Planck Institute for Chemistry.

This research was funded by the French Foundation for Biodiversity Research (FRB) within the Centre for the Synthesis and Analysis of Biodiversity (CESAB) and was co-funded by the Max Planck Institute for Chemistry (MPIC) in Mainz, Germany, the INSU LEFE program and the Initiative d’Excellence d’Aix-Marseille Université – A*MIDEX.