Reviews and syntheses: A trait-based approach to constrain controls on planktic foraminiferal ecology – key trade-offs and current knowledge gaps

Planktic foraminifera are a major contributor to global marine inorganic carbon production. They leave abundant calcium carbonate shells on the seafloor that serve as prime proxies for the physical and chemical attributes of past oceans. Despite their well-preserved fossil record and widespread use in palaeoceanography, our understanding of their ecology remains limited due to their low-standing stocks in the modern ocean and the challenges in culturing multiple generations under laboratory conditions, even after decades of data collection. This limitation affects our ability to interpret their fossil remains to describe past ecosystems and predict their responses to ongoing environmental changes. Trait-based ecology offers a powerful framework to characterise how and why foraminifera interact with their environment. Here, we review the current state of knowledge on key planktic foraminifera 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. Integration of trait-based modelling with metabarcoding, environmental DNA, and enhanced standardised data collection made openly available will help to fill critical gaps in our understanding of planktic foraminiferal ecology and allow us to use foraminifera as a key model organism for addressing fundamental ecological questions.