Microbial Surface Biofilm Responds to the Growth-Reproduction-Senescence Cycle of the Dominant Coral Reef Macroalgae spp.

Macroalgae play an intricate role in microbial-mediated coral reef degradation processes due to the release of dissolved nutrients. However, temporal variabilities of macroalgal surface biofilms and their implication on the wider reef system remain poorly characterized. Here, we study the microbial biofilm of the dominant reef macroalgae over a period of one year at an inshore Great Barrier Reef site (Magnetic Island, Australia). Monthly sampling of the biofilm links the temporal taxonomic and putative functional metabolic microbiome changes, examined using 16S rRNA gene amplicon and metagenomic sequencing, to the pronounced growth-reproduction-senescence cycle of the host. Overall, the macroalgal biofilm was dominated by the heterotrophic phyla (35% ± 5.9% SD) and (12% ± 0.6% SD); their relative abundance ratio shifted significantly along the annual growth-reproduction-senescence cycle of . For example, were 1.7 to 3.9 times more abundant during host growth and reproduction cycles than . Both phyla varied in their carbohydrate degradation capabilities; hence, temporal fluctuations in the carbohydrate availability are potentially linked to the observed shift. Dominant heterotrophic macroalgal biofilm members, such as and , are implicated in exacerbating or ameliorating the release of dissolved nutrients into the ambient environment, though their contribution to microbial-mediated reef degradation processes remains to be determined.