Ecological processes shaping the diversity and biogeography of marine microeukaryotes

Microeukaryotes are diverse with different trophic modes and play important roles in many habitats. Same to other microorganisms, their communities are fundamentally affected by several deterministic (e.g., environmental selection) and stochastic (e.g., ecological drift) processes. How this suite of different processes regulates the biogeography of microeukaryotes remains to be comprehensively explored. In this thesis, microeukaryotic community and its regulating ecological processes were explored at different habitats including coastal, pelagic ocean and cold seep sediment. The results showed that (1) heterogeneous selection mainly regulated the phytoplankton (both eukaryotic and prokaryotic) communities in the Pacific Ocean, with varying relative importance (compared with other processes) across spaces due to the spatial scale, traits of phytoplankton and environmental gradients; (2) Ocean current, by promoting species dispersal, played important roles in the connectivity between local microeukaryotic communities in coastal regions. It largely homogenized the community (by homogenizing dispersal) and reduced the effects of environmental selection, leading to the weak relations between community composition and measured environmental factors; (3) Microeukaryotic communities in the cold seep sediment, represented by abundant and diverse parasitic taxa, were regionally divergent with local phylogenesis. Relative higher species dispersal rate and heterogeneous selection (mainly from metazoans) made active cold seep as hotspots for microeukaryotic diversity. These mechanistic findings deepen our understanding of community ecology of microeukaryotes and provide indications for conservations of marine biodiversity.