Insights into the ecology of epibenthic calcareous foraminifera from a colonization study at 4000 m (Station M) in the NE Pacific Ocean

Abstract Benthic foraminifera are an abundant and important component of modern and ancient deep-sea ecosystems, and these single-celled organisms generate a fossil record that facilitates the assessment of paleoceanographic changes through time. Despite recent advances in taxonomic and ecological information about deep-sea foraminifera, many basic questions remain, requiring a better understanding of ecological tolerances, morphologic plasticity, and distribution of deep-sea foraminiferal species. This study focuses on the phylogenetics, morphology, and colonization dynamics of deep-sea foraminifera at abyssal Station M in the eastern Pacific Ocean. After 368 days at 4000 m on the Pacific Ocean seafloor, 546 foraminifera ∼80% of which were calcareous species, occupied elevated substrate experiments. Genetic analyses of the most abundant calcareous foraminiferal taxon indicate that this trochospiral species is a morphological variant of Cibicidoides wuellerstorfi (referred to as C. wuellerstorfi var. lobatulus). Although Pyrgo and other milioline foraminifera are commonly found within sediments, two morphological variants of Pyrgo colonized elevated substrates at the Station M study site. Many Pyrgo spp. and C. wuellerstorfi var. lobatulus, were covered in an organic cyst, perhaps as a feeding structure. These results suggest that these calcareous foraminifera are able to flourish in deep-sea settings where hard substrates are available, and may be more widely distributed and diverse in lower bathyal and upper abyssal habitats when elevated substrates are present.