Variation in Coral Microbiome Composition and Transcriptional Activity of Three Corals over Diel Cycles

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Caughman, Alicia Marie
Stewart, Frank J.
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Understanding the dynamics of coral microbiome composition and function is important because microbiomes play important roles in coral health and metabolism. While numerous long-term studies have investigated changes in the microbiome due to various physical or biotic stressors, little is known about the stability of the coral microbiome over diel cycle. For certain parameters (e.g., temperature, pH), the magnitude of diel fluctuation can exceed that observed in mean values over seasons, especially on shallow reefs. Such short-term environmental heterogeneity can affect longer term trends, for example by influencing the extent to which corals acclimate to stress and increase resilience. This study examined diel dynamics of microbiomes in three coral species (Porites lutea, Porites cylindrica, and Pocillopora damicornis) from a shallow, backreef lagoon in Mo’orea (French Polynesia). Porites is relatively resistant to stress, being one of the last coral genera to succumb to bleaching or several diseases, and one of the more abundant genera of corals remaining on degraded reefs. In contrast, Pocillopora is less resistant to many of these stresses and bleaches easily but is one of the genera that commonly recruits and rebounds rapidly after disturbances or strong stresses. We assessed microbiome taxonomic composition and relative transcriptional activity by analyzing 16S rRNA gene and transcript sequences from six time points over 48 hours for each of these coral species. Results showed that composition in P. damicornis varied significantly over the diel period, while composition in both Porites species remained more stable. However, the taxonomic composition of the transcript pool did not vary significantly over time across all corals sampled. This shows that diel stability of these coral microbiomes is dependent on host species, which could contribute to differences in host responses to environmental stressors.
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