Plastic waste in marine environments provides novel habitats for diverse organisms, forming distinct microbial ecosystems known as the ‘plastisphere’. Although bacteria of the plastisphere have been widely studied, the role of fungi in plastisphere formation and plastic degradation remains largely unexplored. Thus, we investigated temporal changes in culturable fungal community composition on three common plastic types—high-density polyethylene, low-density polyethylene, and polypropylene—across the early (seven days) and mature (30 days) plastisphere developmental stages through a marine mesocosm experiment. In total, 436 fungal strains were isolated and identified as belonging to 179 taxa, with Penicillium, Cladosporium, Trichoderma, Aspergillus, and Fusarium as the dominant genera. Temporal shifts in the species richness of the dominant genera were observed: Cladosporium showed higher species richness at the early stage, whereas that of Trichoderma increased at the mature stage. Plastic degradation assays revealed that 54.6% of the strains exhibited measurable degradation capacity, with patterns varying by plastic type rather than fungal developmental stage. Scanning electron microscope observations revealed surface damage patterns including cracks, pitting, and erosion on the plastic surfaces. These findings provide novel insights into the composition and functional heterogeneity of culturable fungal communities in the marine plastisphere and suggest that plastisphere fungi play diverse ecological roles beyond direct plastic degradation.