Abstract: The study conducted quarterly investigations in 2023 across Porphyra cultivation areas and control areas of Haizhou Bay to elucidate phytoplankton community dynamics and their responses to aquaculture activities. Results revealed seasonal fluctuating differences in environmental parameters between aquaculture and control regions, particularly in chemical oxygen demand, soluble reactive phosphate, and silicate concentrations. A total of 139 phytoplankton taxa (including varieties) from 5 phyla were identified, with diatoms demonstrating predominance at 51.08% relative abundance. Phytoplankton abundance exhibited significant seasonal variation (p<0.05), peaking at 3.68×10⁸ cells/m³ in winter and decreasing to magnitudes of 10⁵–10⁶ cells/m³ during spring, summer, and autumn, while spatial distribution patterns showed no statistical significance. Cluster analysis revealed distinct seasonal succession characteristics in phytoplankton communities (p<0.05), though no statistically discernible structural differences emerged between aquaculture and control areas. Canonical correspondence analysis identified water temperature, dissolved oxygen, salinity, silicate, and nitrate as key environmental drivers governing phytoplankton assemblage variations. The findings demonstrate that current Porphyra aquaculture practices in Haizhou Bay have not yet induced significant alterations in phytoplankton community structure.