Microeukaryote communities exhibit phyla-specific distance-decay patterns and an intimate link between seawater and sediment habitats in the Western Pacific Ocean

Abstract Microeukaryotes are mainly composed of highly diverse and abundant protists, whose diversity and distribution in deep oceans have not been well studied. We investigated the vertical profiles of microeukaryotes throughout the water column down to abyssal sediments and their horizontal distribution over a distance of 1,300 km in the Western Pacific Ocean, using high throughput DNA sequencing. A distinct vertical distribution was detected for microeukaryote communities, which could be clustered into euphotic, aphotic and sediment groups. Nearly half of the operational taxonomic units detected in the sediment samples were also found in overlying water, indicating a frequent species exchange between seawater habitats and abyssal sediment habitats, which was similar to that observed for prokaryote communities. On the horizontal scaling side, a significant distance-decay relationship was found in the microeukaryote community. Furthermore, the major microeukaryotic groups revealed different distance-decay patterns which appeared to be significant for Dinoflagellata and Radiolaria, but insignificant for Ciliophora. Environmental selection contributed more to the variations in microeukaryote and Dinoflagellata communities than neutral processes, whereas neutral processes explained more variations in Radiolaria community. Generally, community variations explained by both processes were less than 30%, which was lower than that in coastal zones. These results imply that the complex distribution pattern within microeukaryote communities and more drivers, such as currents, water mass and biotic interactions, might contribute in shaping the distribution of microeukaryotes in the open ocean.