Investigating the benefits and costs of spines and diet on planktonic foraminifera distribution with a trait-based ecosystem model

Abstract Planktonic foraminifera are important calcifiers in the modern ocean. Despite this importance, the main functions of foraminifera's test and ornamentation such as spines are unclear. Spinose species dominate the planktonic foraminifera population in subtropical oligotrophic gyres, while non-spinose species dominate in deeper waters and at high latitudes suggesting that spines help foraminifera in food-limited areas. Here we take a novel approach to investigate the benefits of spines on foraminifera foraging using a 0-D trait-based ecosystem model. The model considers the traits of size, calcification, spines, passive feeding, and diet. We assess how the presence of spines impact foraminifera diet and fitness via a series of simulated environments representing oligo, meso- and eutrophic settings at different temperatures. We find that independent of diet, non-spinose taxa need to be more size-generalist predators than other zooplankton species to maintain their population. In contrast, spinose species benefit from a relatively higher surface-to-volume ratio compared to non-spinose species, which allows them to be as generalist as other zooplankton groups. In agreement with observations, we find that herbivory is the most successful diet in cold environments, while carnivory allows foraminifera to be more successful in warm environments.