Colony preparation and acclimation
After collection, the coral colonies were placed in an outdoor tank with opaque roof supplied with unfiltered flowing seawater to acclimate for a week. Each colony was fragmented in four pieces using a tile saw, tagged and all non-coral tissue area was cleaned and covered in reef-safe epoxy. The colony fragments, here referred as “coral nubbins”, were left acclimating in the indoor system for two weeks (ambient temperature 25°C ± 1°C). Using coral nubbins in laboratorial experiments is a way to expose the same colony and microbiome to different treatments, allowing for assessment of genetic variability among treatments, as well as reducing the number of coral colonies collected. The nubbins were monitored and only healthy ones, assessed by recovery of the coring process (outward growth as opposed to tissue regression) and visual endosymbiont function as measured by color and fluorescence readings (Fv/Fm > 0.6) with a pulse amplitude modulated fluorometer (DIVING-PAM Walz Inc.) were used in the experiments.