# Phytoplankton Structure and Ecological Niche Differentiation of Dominant Species in Tahe Bay, China

## TL;DR

This study explores the diversity and ecological niches of phytoplankton in Tahe Bay, China, and how they are influenced by environmental factors.

## Contribution

The study identifies key environmental variables affecting phytoplankton niche differentiation and provides insights for sustainable marine resource management.

## Key findings

- Bacillariophyta dominates the phytoplankton community with high species diversity and resistance to disturbances.
- Paralia sulcata is the most prevalent species except in summer, with seasonal variations in niche overlap.
- COD, water temperature, NO3-N, DIP, NO2-N, and NH3-N are the main factors influencing niche differentiation.

## Abstract

Phytoplankton are the basis of the productivity of the sea area, and understanding the characteristics of the phytoplankton community is a guarantee for the sustainable development of local marine fisheries. A survey was conducted in the waters of Tahe Bay to study the characteristics of the phytoplankton structure and the dominant species’ niche. The results showed that 83 phytoplankton species were identified in six phyla and forty-one genera, dominated by Bacillariophyta, and the phytoplankton community has high species diversity and strong resistance to external disturbances. The dominant species, 20 species in three phyla, mainly consisted of wide-niche species; Paralia sulcata was always the dominant species except in summer. The niche overlap of dominant species was highest in winter, followed by spring, autumn, and summer. The abundance and community diversity of phytoplankton were significantly correlated with environmental variables; an increase in NO3-N and DIP would probably inhibit the growth of species in the Pyrrophyta, Chrysophyta, and Cyanophyta. COD, water temperature, NO3-N, DIP, NO2-N, and NH3-N were the main environmental factors affecting the ecological niche differentiation of dominant phytoplankton species. The results of the study provide scientific references for a deeper understanding of the sustainability of local ecosystems and thus promote high-quality mariculture development.

Phytoplankton serve as crucial producers in marine ecosystems, and their community composition and populations’ dispersion directly or indirectly influence the productivity of marine waters via the trophic cascade effect within the food chain. A survey was undertaken in September 2021 and March, April, and November 2022 to examine the phytoplankton structure and the environmental variables influencing ecological niche differentiation in the waters of Tahe Bay in Lushun, Dalian city, China. The findings indicated that there are 83 species representing forty-one genera and six phyla, with an annual mean abundance of 22.13 × 104 ind·m−3, predominantly represented by Bacillariophyta (65 species, constituting 78.31% of the total species). The phytoplankton richness indices varied from 0.83 to 4.99, diversity indices ranged from 2.03 to 2.80, and evenness indices spanned from 0.28 to 0.84. Pearson’s correlation between phytoplankton abundance and community diversity with environmental parameters, including water temperature, salinity, pH, DO, NH3-N, and NO3-N, was substantial in Tahe Bay’s waters. The dominant species, comprising 20 species across three phyla, primarily include broad-niche species, with Paralia sulcata being the most prevalent species, except during summer. The extent of ecological niche overlap among the dominant species varied by season, exhibiting 40.0% severe overlap in September 2021, 100.0% severe overlap in March 2022, 93.0% severe overlap in April 2022, and 58.0% severe overlap in November 2022. The findings of redundancy analysis (RDA) and canonical correspondence analysis (CCA) revealed that COD, water temperature, NO3-N, DIP, NO2-N, and NH3-N are the primary environmental variables influencing the ecological niche differentiation of dominant species of phytoplankton. The results of the study elucidate the alteration rules of dominant species and the stability of the community structure of the phytoplankton community in this sea area, thereby offering a theoretical foundation for the scientific assessment of the ecological health of the area and the sustainable utilization of marine biological resources.