The FORCIS project (Foraminifera Response to Climatic Stress: evaluating biodiversity changes of calcifying zooplankton in response to multiple stressors), and Mediterranean context for the response of planktonic foraminifera

Anthropogenic carbon dioxide (CO₂) emissions lead not only to oceanic warming, but also to a decrease in the pH of surface waters. Such ocean acidification is known to affect the calcifying marine biota, a key component of the carbonate pump. Fossilized shells of planktonic foraminifera constitute one of the sources of carbonate to the deep sea, making it particularly important to understand the dynamics of this clade in a changing climate. Yet, historical changes in planktonic foraminiferal assemblages have not been synthesized on the global scale, although there is some evidence that they are already likely responding to anthropogenic changes in the ocean.

In order to assess these changes, the FORCIS working group is working on a synthesis of historical plankton nets, combined with available Continuous Plankton Recorder (CPR) and sediment trap datasets. We have compiled a comprehensive database of all available foraminiferal census data and accompanying hydrographic data when available from plankton samples collected since the early 1950’s. To date, our database gathers >44000 CPR data ; >1400 sediment trap datasets and >2600 plankton nets. These datasets were collected from 1950 to 2019 and combine both published and unpublished datasets from the working group members.

A first analysis of the database indicates that the standing stock of planktonic foraminifera spans several orders of magnitude, reaching thousands of foraminifera per cubic meters. This first analysis does not allow detection of a significant trend in the absolute abundance of foraminifera, though absolute abundance of foraminifera retrieved from finer nets seems to decrease after the 1980’s.

Here we will present this new synthesis to yield insights into (i) spatial (ii) vertical and (iii) seasonal patterns of planktonic foraminifera over the last decades. We will also highlight the Mediterranean Sea as an interesting and suitable microcosm of the global pattern. These new insights on the ecology of planktonic foraminifera will then be used to improve ecophysiological and population dynamics models for this taxon.