Temperature-driven shifts in fungal community structure and potential pathogen prevalence in the surface water of Yangshan Deep-Water Harbor

Fungi represent a diverse and ecologically significant group of eukaryotic microorganisms. Here, we characterized fungal diversity in the surface water of Yangshan Deep-Water Harbor (YH)—a dynamic brackish habitat influenced by both Yangtze River freshwater and East China Sea seawater—using an internal transcribed spacer 1 (ITS1) based metagenomic approach. Our results reveal that fungal communities in YH are strongly shaped by water temperature, with samples at 20 °C showing greater similarity to those at 10 °C than to those at 30 °C, and overall communities more closely resembling seawater than freshwater assemblages. We further found that bacterial communities co-influence fungal diversity, and that fungal assemblages in YH exhibit relatively low ecological stability. Taxonomically, Ascomycota and Basidiomycota dominated among classified fungi, while a substantial proportion of fungal phylotypes (1,344 operational taxonomic units [OTUs], 51.4% of sequences) remained unclassified. Notably, Candida parapsilosis, a common opportunistic human pathogen, represented over 60% of sequences in YH samples at 20 °C, likely reflecting inputs from human-impacted coastal freshwater sources. This study highlights the ecological complexity of YH and underscores the role of anthropogenic activities in shaping its fungal communities.