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 the epibiome of 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 Fokiniaceae (MD3-55 genus) and Cyanobacteria (Synechococccus). The abundances of these bacterial taxa varied consistently between genotypes whereas neither the composition nor taxonomic 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.

22Remote populations can influence connectivity and may serve as refugia from climate 23 change. Here, we investigated two reef-building corals (Pseudodiploria strigosa and 24Orbicella franksi) from the Flower Garden Banks (FGB)the most isolated, high-25 latitude Caribbean reef system that retains high coral cover. We characterized coral size 26 frequency distributions, quantified larval mortality rates and onset of competence, 27 estimated larval production, and created detailed biophysical models incorporating these 28 parameters to evaluate source-sink dynamics from 2009 to 2012. Mortality rates were 29 similar across species but competency differed dramatically: P. strigosa was capable of 30 metamorphosis within 2.5 days post fertilization (dpf), while O. franksi were not 31 competent until >20dpf and remained competent up to 120dpf. Despite these differences, 32models demonstrated that larvae of both types were similarly successful in reseeding the 33 FGB. Nevertheless, corals with shorter pelagic larval durations (PLD), such as P. 34 strigosa, were highly isolated from the rest of the Caribbean, while long PLD corals, such 35as O. franksi, could export larvae to distant northern Caribbean reefs. These results 36suggest that FGB coral populations are self-sustaining and highlight the potential of long 37PLD corals, such as endangered Orbicella, to act as larval sources for other degraded 38Caribbean reefs. 39 40 20 dpf for the short-PLD model (P. strigosalike) and 20 to 120 dpf for the long-PLD 107 model (O. franksilike). 108