Long-term variation in coral microbiome

The coral microbiome is known to fluctuate in response to environmental variation and has been suggested to vary seasonally. However, most studies to date, particularly on bacterial communities, have examined temporal variation on a less than one-year time frame, which is insufficient to establish if microbiome variations are indeed seasonal in nature. Here, we aimed to expand our understanding of long-term variability in microbial community composition using two common branching coral species, Acropora hyacinthus and Acropora spathulata at two mid-shelf reefs on the Great Barrier Reef, by determining whether temporal variations reflect seasonal cycles over a two-year time period. Community composition of both bacteria and Symbiodiniaceae was characterized through 16S rRNA gene and ITS2 rDNA metabarcoding. The results of this study confirm that the coral microbiome is both dynamic and complex in nature, with significant variations in community composition of both bacteria and Symbiodiniaceae present among time points for A. hyacinthus and A. spathulata. However, there was no evidence to suggest that these temporal variations were cyclical in nature and represented seasonal variation. We suggest that in order to identify the basis of temporal patterns in coral microbial community composition, future studies need to use longer time series of sampling at sufficient resolution to identify the environmental correlates of microbiome variation.