Abstract: Biofouling organisms are a major factor affecting the power generation efficiency and operational safety of offshore floating photovoltaic (FPV) systems. To support material selection and biofouling control of FPV panel bases in subtropical seas of China, a two-year simulated panel suspension experiment was conducted in Dongshan Bay, a typical subtropical bay along the southeastern coast of China. A total of 101 species of macrofouling organisms were identified. Results showed that the intensity of biofouling attachment was significantly higher in spring and summer than in autumn and winter. The dominant species varied among panel materials: Amphibalanus reticulus predominated on Antimicrobial Boards, Ultra High Molecular Weight Polyethylene Boards, Concrete Boards, and High-Density Polyethylene Boards, whereas Obelia sp. and Botryllus sp. were dominant on Isolation Mesh Boards and Plush-covered Boards. Among all tested materials, High-Density Polyethylene Boards exhibited the highest annual average density (19289 ind/m²), biomass (889.5 g/m²), and attachment thickness (2.9 mm). In contrast, the lowest values were observed for settlement density on Isolation Mesh Boards and Antimicrobial Boards (5323 ind/m²), biomass on Ultra High Molecular Weight Polyethylene Boards (50.9 g/m²), and attachment thickness on Concrete Boards (1.3 mm). During the successional process, the maximum density (139504 ind/m²) was recorded on Antimicrobial Boards, while the maximum biomass (3386.8 g/m²) occurred on High-Density Polyethylene Boards; both minimum values were observed on Ultra High Molecular Weight Polyethylene Boards (21426 ind/m², 484.8 g/m²). Considering five integrated indicators—proportion of calcareous-shell organisms, biomass, surface coverage, attachment thickness, and cumulative biomass— Plush-covered Boards and Ultra High Molecular Weight Polyethylene Boards showed the lowest fouling intensity.