Uncovering fungal diversity in mangroves: new records, ecological insights, and phylogenetic analysis of Ascocylindrica marina from Tarout Island, Saudi Arabia

Abstract

This study investigated the diversity and ecological patterns of marine fungi associated with decayed Avicennia marina wood in the mangrove ecosystems of Tarout Island, Saudi Arabia. A total of 17 fungal species were isolated from four distinct mangrove stands that varied in vegetation density and environmental characteristics. These included ten teleomorphic ascomycetes and seven anamorphic fungi. Notably, 15 species were recorded for the first time from Tarout Island, and 13 species represent new records for the marine mycobiota of Saudi Arabia. Ascocylindrica marina was the most frequently encountered species, accounting for 30.07% of total isolates. Morphological identification was supported by scanning electron microscopy (SEM), revealing characteristic features such as erumpent ascomata and rough-walled ascospores. Molecular identification was conducted using large subunit (LSU) and small subunit (SSU) rDNA sequencing, and phylogenetic analysis confirmed the placement of A. marina within the family Ascocylindraceae. Environmental data collected from each stand revealed significant correlations between fungal diversity and key abiotic factors. Species richness showed a strong positive correlation with sediment nitrogen concentration (r = 0.72, p < 0.05), while the abundance of A. marina was positively associated with high salinity levels (r = 0.85, p < 0.05). Canonical correspondence analysis (CCA) further confirmed that salinity and nutrient availability were the main environmental variables shaping fungal community composition. The findings provide new insights into the underexplored marine fungal biodiversity of Arabian Gulf mangroves and underscore the ecological specialization of halotolerant fungi. The study highlights the potential of these organisms for use in biotechnological applications, particularly those requiring tolerance to high salinity and nutrient-stressed environments.