Abstract
In order to mitigate the loss experienced by coral reef ecosystems, coral outplanting has become increasingly popular. Despite the success of this method, there is still high variation in the survivorship of out planted corals due to heat stress, disease, and environmental variation that wiped out prior wild populations. Today, scientists are searching for corals that exhibit resilience or resistance to these conditions for continued success in the future. This relative “resistance” can be attributed to genotypic variation as well as microbiome variation within the host coral. Previously in 2016, a field disease grafting assay was conducted with nursery-reared Acropora palmata and Acropora cervicornis to begin quantifying disease susceptibility by genotype. This assay was conducted on two separate occasions, first in the summer of 2016, and then the following summer of 2017. In this study, the microbiome from 2016 samples were investigated for its own microbiome patterns and differences as well as compared to the microbiome results previously determined from the 2017 samples (Rosales et al.2019). To do so, a 16S rRNA gene high-throughput sequencing was done on both control and disease samples. Based on the analysis of the 16S RNA sequences, A. palmata and A. cervicornis have distinctly different microbiome patterns independent of treatment. In addition, dominant microbes were identified in both species from control and experimental samples. The bacteria type that dominated A. cervicornis samples was classified to the genus level as MD3-55, part of the larger phylum of Proteobacteria. This bacterium has been previously identified as a possible parasitic pathogen often associated with White Band Disease (WBD), however it has also been observed to be common within A. cervicornis without any pathogenic effects. The most prominent bacteria present in the A. palmata is classified to the genus level as Spirochaeta 2of the phylum Spirochaetes. There is not much known about this species and its relationship to coral yet, however it is part of a taxa noted to have nitrogen-fixing abilities and prevalence among the microbiomes of other coral species. In addition, Rhizobiaceae (phylum Proteobacteria) was identified to be a potential pathogen, especially in A. cervicornis, and Brevundimonas (phylum Proteobacteria) was identified in A. palmata as a potentially beneficial microbe.