a–d Host phylogenies are inferred from COI, 18S rRNA and ITS1 sequences while microbial dendrograms are based on Bray–Curtis dissimilarity for microbial composition of each host species. Cladiella sp. was used as an outgroup for a sponges, while C. foliascens was used as an outgroup for b coral, c octocoral and d ascidians. Numbers at nodes reflect posterior probability for clade support in host trees and jackknife support values in dendrograms. Branch tips are coloured to reflect clades in host phylogeny. Initials in brackets next to species names refer to collection site. BR Broadhurst Reef, DR Davies Reef, OR Osprey Reef, PI Palm Islands (Orpheus and Pelorus), PR Pandora Reef, RB Rib Reef, RR Ribbon Reefs. P. massive refers to massive Porites sp.