Seasonal Changes in Aquatic Fungal Communities of a Coastal Lagoon (Ria de Aveiro, Portugal)

Despite the ecological and economic importance of Ria de Aveiro, Portugal, little is known about the diversity and seasonal dynamics of fungal communities. We analysed fungal communities in water samples from eight sites, during four seasonal campaigns, using DNA metabarcoding of the ITS1 region. A total of 12,929 ASVs (1,871,816 reads) were obtained, affiliated with 16 fungal phyla, though 33.9% of the reads could not be assigned at phylum level. The most abundant phyla throughout the year were Ascomycota, Basidiomycota, and Mortierellomycota, with Aspergillus, Cladosporium, and Fusarium being the most represented genera. Fungal richness did not vary among seasons, and evenness was lower in winter than in summer, mainly due to two samples. Fungal composition differed among seasons, mainly between winter and the other seasons. The winter change was associated with a higher proportion of reads without phylum assignment (putatively fungal), and the two dominant unassigned ASVs had no close relative in reference databases. Temperature, salinity, and dissolved oxygen were correlated with evenness and with the relative abundance of several fungal families, most of which were less abundant in winter. To our knowledge, this study provides the first overview of fungal communities in the water column of the Ria de Aveiro estuary.