New coral associated fungi found at Curacao

Abstract

One of the most biologically diverse ecosystems on earth are tropical coral reefs. It is the habitat for one-third of the marine fish species for at least part of their life cycle. Hard corals are the major structural builders of this system. Nowadays, knowledge of the microbiome of corals is mainly focused on bacteria and symbiotic zooxanthellae. Thus, the importance of fungal coral interactions remains unrevealed which may be both beneficial and pathogenic.Only recently more marine fungi have been studied due to an increase in corals affected by pathogenic fungi. We extended these studies by cultivating endolithic fungi from healthy and diseased coral Sidrastrea siderea, as well as healthy corals of the species Agaricia agaricites, Montastraea annularis, Madracis mirabilis, Stephanocoenia intersepta and Montastraea cavernosa from the reef of Curacao in the Caribbean Sea. Sterilisation by UV light turned out to be a successful method to kill microorganisms at the surface of the coral without affecting the fungi from the internal part. A total of 90 colonies originating from internal parts of corals were purified on plates based on visual inspection, while 4species were found based on DNA sequencing. Newly found coral associated fungi were Aspergillus tamarii, Penicillium solitum, Aspergillus flavus or Aspergillus oryzae, Aspergillus tubingensis, Aspergillus penicillioides, Penicillium citrinum, and Penicillium westlingii. Aspergillus versicolor, Aspergillus sydowii, were identified in this study as well as in previous studies. Notably, a higher diversity of fungi was cultured from healthy than from diseased S. siderea coral. The identified fungi and what is known from these species suggest that coral associated fungi act as pathogens, bio-eroders, bio-borers, but may also be beneficial as being part of the coral microbiome. In the latter case it may produce mycotoxins, antibacterial, and / or fungal metabolites to protect the coral and its microbiome. In future studies, it would be interesting to combine metagenomics with the approach that was adopted in this study, especially since fungi play a bigger role in coral ecosystems than assumed so far.