Why might you want fungus in your skeleton?

Fungi grow epi- and endo-biontically in reef corals and some even bore into coral skeleton.  Goés-Neto et al. used 18S rRNA metabarcoding to identify endolithic fungi from 11 coral genera from around Australia and PNG.  At 97% similarity over 90% of OTUs were matched to reference sequences and FunGuild was used to classify OTUs by broad trophic mode.

Most OTUs were Ascomycota or Basidiomycota, a few of which had never been associated with corals before, and at least some of the 8% unassigned OTUs may be new to science. There was great diversity in fungal communities between coral taxa with Porites showing most fungal genera. Most fungal OTUs were, unsurprisingly, classed as saprotrophs, including the most common genera, Lulworthia and Lulwoana, which occur across a wide geographical range.  

This paper is valuable in revealing the fungi present within coral.  Sampling was, however, skewed towards Porites (17 of 25 samples); more balanced sampling may show greater diversity in other coral genera which were limited to one individual.  Other research has found fungal genes which reduce nitrate and assimilate ammonia suggesting fungi may have important nutrient recycling roles in oligotrophic oceans.  Further Metagenome/transcriptone work would be needed to illuminate detailed fungal functions.

GOÉS-NETO, A., MARCELINO, V. R., VERBRUGGEN, H., DA SILVA, F. F. & BADOTTI, F. Biodiversity of endolithic fungi in coral skeletons and other reef substrates revealed with 18S rDNA metabarcoding. Coral Reefs.