Distribution and influencing factors of microeukaryote in different water layers of the southwestern Indian Ocean Ridge

Microeukaryotes play a vital role in shaping marine ecosystems, especially in marine productivity, the microbial food web, and carbon cycle. The Indian Ocean is one of the largest oligotrophic areas in the world, but little is known about the biodiversity of microeukaryotes in the area. The community composition and geographical distribution of microeukaryotes collected from the surface (SUR) and deep chlorophyll maximum (DCM) layers in the southwestern Indian Ocean were studied using high-throughput sequencing of the 18S rRNA gene. The metagenomic data helped quantify the impact of environmental factors on microeukaryotic communities. The relative abundance of different taxa groups exhibited distinct patterns between SUR and DCM layers, except for the most dominant Dinoflagellata that accounted for more than 40.6% abundance in each sample. Radiolaria was much more abundant in the nutrient-rich DCM layer than the SUR layer. The community similarity of microeukaryotes decreased with increasing of geographic distance, whereas the temperature and inorganic nitrogen were the most important environmental parameters to community structure. Abundant communities were more influenced by dispersal limitations and rare communities were more responsive to environmental factors. Correlation network analyses revealed strong biotic interactions indicative of parasitism, predation and competition, and their contribution to microeukaryotic population in diverse environments. Overall, this study provided insights into the biodiversity of microeukaryotes by characterizing the differences between water layers and identifying the driving factors in the ocean.