Bacterial taxa
Ruegeria  and Roseobacter significantly increased in relative abundance in response heat stress (Fig. 2). High abundances of Rhodobacterales such as Ruegeria  and Roseobacter in juvenile and adult corals suggest they play a key role in coral fitness (Ceh et al. 2013a; Zhou et al. 2017), nitrogen acquisition and remineralization (Ceh et al. 2013b; McNally et al. 2017), and sulfur cycling (Raina et al. 2013). Ruegeria are among the three genera that are most frequently associated with coral species (Hugget and Appril 2019). Some strains of Ruegeria have probiotic potential as they can inhibit growth of pathogen Vibrio coralliilyticus(Miura et al. 2019) and support corals to withstand heat stress (Rosado et al. 2019, Kitamura et al. 2021, Santoro et al. 2021). In fact,Vibrio decreased in relative abundance in the coral microbiome under heat treatment (Fig. 2), indicating that P. strigosa was able to keep these potential pathogens in check. Lower abundances ofSynechococcus after heat stress (Fig. 2) could be an indication that corals are using these cyanobacteria as an energy and nutrient source via heterotrophic feeding to compensate for lower productivity of the algal symbiont (Fig. 1). Corals can preferentially feed onSynechococcus , especially to recover from heat stress and bleaching (McNally et al. 2017; Meunier et al. 2019; Hoadley et al. 2021).