Celestine Nwojiji^{1, 2,}, Bryony Caswell³, Fabienne Marret¹

Foraminifera are marine microorganisms which provide essential ecological functions in the oceans. They are very sensitive to the physio-chemical changes in the marine environment and tend to incorporate the changes in the environment they lived into their test during calcification. The records of the changes in their test serves as a black box for the changes in ocean ecology over time. In view of current changes in the global marine ecosystem as a result of anthropogenic and natural pressures, it is important to understand the reaction of foraminifera (both at the community level and individual attributes) to the late Palaeocene - early Eocene hyperthemal event [the Palaeocene-Eocene thermal maximum (PETM)]. The PETM was a global warming event that occurred 55 million years ago. It resulted in the acidification of the deep sea, shoaling of the lysocline and Carbon Compensation Depth (CCD), massive extinction of benthic foraminifera as well as diversification and migration of both marine and terrestrial organisms. This study used Biological Trait Analysis (BTA) to understand the changes in foraminiferal population and trait composition during the PETM. The results from this study demonstrated that BTA techniques could be used to detect ecological disturbance based on non-metric multi-dimensional scaling (nmMDS) ordination. The nmMDS ordination of all the studied sites showed wider separation during environmental disturbance [period of negative Carbon Isotopic Excursion (CIE)] compared to other intervals. Thirteen (13) foraminiferal traits and over 60 trait categories were perceived to be crucial for the foraminiferal ecological functioning in the marine environment. However, BTA recognised test composition, chamber arrangement/ shape, ornamentation, primary aperture position, perforations and living/feeding habit as the most important foraminiferal trait in the benthic ecosystem. Traits such infauna and sessile life habits; cylindrical elongate and bi-triserial test forms; complex terminal apertures and omnivorous feeding modes were the most resilient traits during the hyperthermal.

PETM, benthic foraminifera, palaeooceanography, palaeocology, extreme climate, biological traits