Abstract. The stratification of the upper oligotrophic ocean has a direct
impact on biogeochemistry by regulating the components of the upper-ocean
environment that are critical to biological productivity, such as light
availability for photosynthesis and nutrient supply from the deep ocean. We
investigated the spatial distribution pattern and diversity of phytoplankton
communities in the western Pacific Ocean (WPO) in the autumn of 2016, 2017,
and 2018. Our results showed the phytoplankton community structure mainly
consisted of cyanobacteria, diatoms, and dinoflagellates, while the
abundance of Chrysophyceae was negligible. Phytoplankton abundance was high
from the equatorial region to 10∘ N and decreased with
increasing latitude in spatial distribution. Phytoplankton also showed a
strong variation in the vertical distribution. The potential influences of
physicochemical parameters on phytoplankton abundance were analyzed by a
structural equation model (SEM) to determine nutrient ratios driven by
vertical stratification to regulate phytoplankton community structure in the
typical oligotrophic ocean. Regions with strong vertical stratification were
more favorable for cyanobacteria, whereas weak vertical stratification was
more conducive to diatoms and dinoflagellates. Our study shows that
stratification is a major determinant of phytoplankton community structure
and highlights that physical processes in the ocean control phytoplankton
community structure by driving the balance of chemical elements, providing a
database to better predict models of changes in phytoplankton community
structure under future ocean scenarios.
Seasonal analysis of protistan community structure and diversity at the USC Microbial Observatory (San Pedro Channel, North Pacific Ocean)
