Different phytoplankton distributions and assembly processes in marine water masses with contrasting nutrient...

Phytoplankton play a vital role in global primary production and carbon fixation in marine ecosystems. A comprehensive understanding of their distribution patterns and assembly mechanisms under different nutrient conditions is essential for phytoplankton ecology. However, research in this field remains insufficient.

This study used environmental DNA (eDNA) technology targeting the 23S rRNA gene of phytoplankton to investigate the community structure and assembly processes of phytoplankton (algae and cyanobacteria) in the East China Sea. The analysis identified 224 phytoplankton species, including 72 Bacillariophyta, 44 Cyanobacteria, and 34 Chlorophyta. Based on the relative proportion of each phytoplankton 23S rRNA gene in the sequencing data, Bacillariophyta and Dinoflagellata were found to be predominated in the nutrient-rich Changjiang Diluted Water (CDW), while cyanobacteria dominated in the low-nutrient Kuroshio Branch Current (KBC). The distribution of phytoplankton was significantly influenced by salinity and nutrient levels. Deterministic processes primarily governed community assembly in both the CDW and the KBC. Co-occurrence network analysis revealed stronger phytoplankton interactions in the KBC compared to the CDW, suggesting enhanced cooperative or competitive dynamics. The CDW network, on the other hand, exhibited more modules, likely due to greater environmental heterogeneity.

This study highlights the effectiveness of eDNA technology in elucidating phytoplankton community structure and assembly mechanisms across diverse nutrient environments. These findings enhance our understanding of the ecological impacts of relatively high nutrient concentrations on phytoplankton in a changing ocean.