Host performance related OTUs
Some OTUs that were strongly correlated may represent taxa affecting host performance. For instance, OTU2 (classified toGranulosicoccus ), which is an abundant core member of theG. vermiculophylla holobiont (Bonthond et al., 2020). Also in the present experiment it was detected in high numbers as epiphyte and correlated positively with growth (Figure S2C). Granulosicoccusspecies have also been detected in high abundances (Ramirez-Puebla et al., 2020) or as core microbiota (Park, Davis, Lajoie, & Parfrey, 2022) on other seaweeds. OTU8, (classified to Schizothrix ) is a core OTU (Bonthond et al., 2020) correlating negatively with thallus brittleness, which could hint at a protective role within the holobiont (Saha & Weinberger, 2019).