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).