Host-specific epibiomes of distinct Acropora cervicornis genotypes persist after field transplantation

Abstract

Microbiome studies across taxa have established the influence of host genotype on microbial recruitment and maintenance. However, research exploring host-specific epibionts in scleractinian corals is scant, and the influence of intraspecific differences across environments remains unclear. Here, we studied ten Acropora cervicornis genotypes to investigate the relative roles of host genotype and environment in structuring the epibiome. Coral mucus was sampled in a common garden nursery from replicate ramets of distinct genotypes (T0). Coral fragment replicates (n = 3) of each genotype were then transplanted to nine different field sites in the Lower Florida Keys, and mucus was again sampled one year later from surviving ramets (T12). 16S rRNA amplicon sequencing was used to assess microbial composition, richness, and beta-diversity. The most abundant and consistent amplicon sequencing variants (ASVs) in all samples belonged to Midichloriaceae (MD3-55 genus) and Cyanobacteria (Synechococccus). The relative abundances of these bacterial taxa varied consistently between genotypes, whereas neither the composition nor taxonomic relative abundance were significantly different among field sites. Interestingly, several high MD3-55 hosting genotypes showed rapid diversification and an increase in MD3-55 following transplantation. Overall, our results indicate healthy A. cervicornis genotypes retain distinct epibiome signatures through time, suggesting a strong host component. Lastly, our results show that differences in MD3-55 abundances can be consistently detected in the epibiome of distinct host genotypes of A. cervicornis. As this organism (sensu Aquarickettsia rohweri) has been implicated as a marker of disease resistance, this finding reinforces the potential use of microbial indicators in reef restoration efforts via non-invasive surface/mucus sampling.