Reef-building scleractinian corals are complex holobionts composed of the coral host and a diverse, dynamic microbiome that includes symbiotic microalgae of the family Symbiodiniaceae, as well as bacteria, archaea, viruses, and fungi. This consortium plays a central role in coral nutrition, particularly in tropical reef environments characterized by strong oligotrophy. Under optimal environmental conditions, photosynthetic symbionts provide the primary source of energy to the coral host through autotrophic carbon fixation, supplying up to 95% of the coral’s metabolic carbon demand and thereby sustaining calcification, growth, and reef persistence over time. Additionally, associated bacterial communities contribute to nutrient recycling, specifically through nitrogen cycling pathways that support holobiont functioning.
Under environmental stress, especially during marine heatwaves, symbiosis stability can be disrupted. Expulsion or loss of algal symbionts leads to coral bleaching and a drastic reduction in photosynthetically derived energy. During such events, the microbial community may play a critical compensatory role by maintaining nutrient recycling processes, promoting heterotrophic feeding on organic matter, and contributing to host resistance and post-stress recovery mechanisms.
This study aims to investigate differences in microbiome composition and structure according to the health status of three coral species. Healthy corals are commonly associated with stable and functionally integrated microbial assemblages, whereas bleached corals often exhibit microbial dysbiosis. High-throughput sequencing approaches targeting the ITS2 (Internal Transcribed Spacer 2) region, the reference marker for characterizing lineages within Symbiodiniaceae, and bacterial 16S rRNA gene are employed to link microbiome structure with nutritional functions and resilience mechanisms of the coral holobiont in the context of ongoing climate change.
