Analysis of phytoplankton community structure and its relationship with environmental factors in coastal waters of eastern Leizhou Peninsula during spring and autumn

Based on the seasonal net sampling conducted in the coastal waters of the eastern Leizhou Peninsula during spring and autumn of 2023, we investigated the structural characteristics of the phytoplankton community and its relationship with environmental factors. A total of 131 species of phytoplankton which belong to 5 phyla and 44 genera had been identified, including 105 species of Bacillariophyta, 24 species of Pyrrhophyta, and one species each of Chrysophyta, Euglenophyta and Haptophyta. Bacillariophyta was the dominant group in both spring and autumn. The dominant species in spring were Rhizosolenia styliformis var. longispina, Leptocylindrus danicus, and Thalassiosira subtilis, while the dominant species was Skeletonema costatum in autumn. The average phytoplankton abundances were 9.1×10⁶ cells·m⁻³ in spring and 3.0×10⁸ cells·m⁻³ in autumn, respectively. In spring, phytoplankton abundance exhibited a trend of being higher nearshore and decreasing offshore, whereas in autumn, the abundance was higher offshore and lower nearshore. The proportion of Bacillariophyta exceeded 97.6% in both seasons. Phytoplankton diversity was high in both spring and autumn (Diversity level I), and could be divided into two sub-communities in each season. Redundancy analysis indicates that the primary environmental factors influencing the phytoplankton community structure in this region during spring were temperature, transparency, pH, dissolved oxygen, inorganic nitrogen and inorganic phosphorus, while during autumn, the main factors were salinity, temperature and chlorophyll a (p<0.01).