Molecular diversity and spatial distribution of benthic foraminifera of the seamounts and adjacent abyssal plains in the tropical Western Pacific Ocean

Deep-sea systems are among the least understood ecosystems on Earth. Forming large proportions of deep-sea benthic communities, benthic foraminifera play important roles; however, their molecular diversity and distribution patterns in the deep-sea seamounts and abyssal plains of the tropical Western Pacific Ocean are poorly known. In this study, using next-generation sequencing, we investigated the molecular diversities and community compositions of benthic foraminifera of the tropical Western Pacific Ocean seamounts and adjacent abyssal plains, with water depth ranging between 263 and 5900 m. A region of the small subunit (SSU) rRNA gene (about 300 bp) was amplified with the foraminiferal-specific primers (s14F3-s17), and the PR2 database was selected as the reference database for sequence assignment. Monothalamiids were assigned most of the 1399 operational taxonomic units (OTUs) obtained. The foraminifera genetic novelty, with an average similarity of 91.33% to reference sequences in the deep sea, was extremely high. Comparing the different habitats, the foraminiferal diversities of the seamounts investigated were both higher than those of their adjacent abyssal plains. Clustering of results showed the foraminifera community composition of the Y3 Seamount to be most like that of its adjacent abyssal plain. Our study indicates that the foraminiferal diversity distribution patterns and community structures between the two seamounts differ, yet they resemble those of their adjacent abyssal plain areas. We infer the possibilities that seamounts are diversity hotspots, possessing particularly high benthic species richness, and that foraminifera spread from them to the adjacent abyssal plains. The results also revealed variations in foraminifera at different water depths and temperatures in seamounts and adjacent abyssal plains. Additionally, an extremely high genetic novelty of foraminifera was observed in these habitats, which points to a hotspot for the discovery of new foraminifera species in deep-sea systems.