Reviews and Syntheses: Trait-based approach to constrain controls on planktic foraminiferal ecology: key trade-offs and current knowledge gaps 

Abstract. Planktic foraminifera are a major contributor to marine inorganic carbon production. They leave abundant calcium carbonate shells on the sea floor, which serve as prime proxies for the physical and chemical attributes of past oceans. Despite a well-preserved fossil record and wide use in palaeoceanography, our understanding of their ecology is limited due to their low-standing stocks in the modern surface ocean and the challenges in culturing multiple generations under laboratory conditions, even after decades of data collection. This limitation affects our ability to use their fossil remains to describe past ecosystems and predict their responses to modern environmental changes. Trait-based ecology can be particularly useful at characterising how and why foraminifera might interact with their environment. Here, we review the state of knowledge of planktic foraminifera key traits, including morphological, physiological, behavioural and life history traits. Most spinose taxa are carnivorous, host to dinoflagellate photosymbionts, and are abundant and diverse in oligotrophic environments. In contrast, non-spinose taxa are typically herbivorous and most common in high-productivity regions. We highlight the potential of trait modelling to generate hypotheses testable in the field. We propose that trait modelling, metabarcoding, eDNA, and enhanced standardised data collection, released in open data, can help fill critical gaps in our understanding of planktic foraminiferal trait-based ecology and allow us to use foraminifera as a key model organism for ecological questions.