Biodiversity of endolithic fungi in coral skeletons and other reef substrates revealed with 18S rDNA metabarcoding

Corals live in close association with a diverse community of eukaryotes, bacteria, archaea and viruses that, together with the coral host, form the coral holobiont. Fungi are an important component of the coral holobiont; however, knowledge about their taxonomic diversity and the ecological functions these organisms play in reef corals is still scarce. In this study, we used metabarcoding to characterize the fungal community inhabiting the skeleton of eleven coral genera, as well as samples of crustose coralline algae, from Australia and Papua New Guinea. Most of the 24 distinct fungal genera identified were assigned to the phylum Ascomycota, followed by Basidiomycota. Lulworthia and Lulwoana (Ascomycota) were the most abundant and prevalent genera detected in our study. Besides these widely distributed genera, others never associated with corals or marine environments before, such as Geranomyces (Chytriomycota), Flammulina (Basidiomycota) and Ophiosphaerella (Ascomycota), were also detected. The predicted functional groups give insights into potential lifestyles and ecological functions of the fungal community in reef ecosystems. This study provides important observational data on a group of holobiont members that has received little attention.