Abstract: To explore the factors influencing the population dynamics of macroalgae and benthic fauna in the marine area surrounding Lvhua Island, this study conducted field ecological surveys employing methods such as the Index of Relative Importance (IRI), biodiversity indices, and Canonical Correspondence Analysis (CCA). These methods were applied across three growth stages of macroalgae in the algal beds: seedling (August-September 2021), growth (November-December 2021), and flourishing (May-June 2022), to analyze the community composition, biodiversity, and environmental factors related to population changes of macrobenthic organisms in Lvhua Island and its adjacent waters. The results indicated that: (1) A total of 113 species of macrobenthic organisms were identified in the algal beds of Lvhua Island and its neighboring waters, including 49 species of benthic fauna and 64 species of macroalgae, belonging to nine phyla. Among the taxa, the phylum Mollusca and Rhodophyta had the highest number of species, with Rhodophyta consistently dominating species diversity across all observed periods. Sargassum vachellianum, Sargassum horneri, Chlorostoma rustica, and Anthocidaris crassispina were identified as the dominant species. The average abundance of the nine phyla across the three growth stages was 30 ind·m^-2, and the average biomass was 23.83 g·m^-2. (2) The number of species varied across growth stages, with the highest species richness observed during the seedling stage. The variation in abundance and biomass was closely linked to the periodic changes in water temperature, with abundance following the order of seedling stage (36 ind·m^-2) > flourishing stage (30 ind·m^-2) > growth stage (23 ind·m^-2), while biomass also varied as seedling stage (25.40 g·m^-2) > flourishing stage (23.88 g·m^-2) > growth stage (22.20 g·m^-2). Principal Coordinates Analysis (PCoA) indicated significant differences in the structure of macrobenthic communities across different growth stages (P<0.05). (3) The Mentoushan station exhibited the highest species richness, abundance, biomass, and biodiversity, while Menduishan station had the lowest diversity, and the Xilvhua station had the fewest species. The dominant and important species differed little at the Donglvhua South station, where both biomass and abundance were at the lowest levels, whereas the overlap of dominant and important species was relatively low in the mussel farming area. (4) With the exception of salinity, water temperature (P=0.009), pH (P=0.001), and dissolved oxygen (P=0.002) were significant environmental factors influencing the distribution of macrobenthic organisms in the waters around Lvhua Island, while the effect of salinity (P=0.149) was not significant. The adaptability of organisms to environmental factors varied among stations, with Mentoushan and Menduishan stations showing a positive correlation with the four environmental factors, while Yibeidi, Xilvhua, and Donglvhua North stations showed negative correlations. Among the nine phyla, Phaeophyta exhibited a negative correlation with all four environmental factors, while salinity showed a positive correlation with Cnidaria. This study contributes to a deeper understanding of the regulatory role of macrobenthic organisms within the algal bed ecosystem and provides a scientific basis for the conservation and utilization of biological resources, algal bed construction, and ecological restoration in the study area.

Key words: Lvhua Island, seaweed beds, macroalgae, macrozoobenthos, growth stages, environmental factors