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In the present study, we used Illumina sequencing to explore the prokaryote communities of 17 demosponge species and how they compare with bacterial mat, sediment and seawater samples (all sampled from coral reef habitat in Taiwan and Thailand). The studied sponge species formed three clusters. Operational taxonomic unit (OTU) richness and evenness were by far highest in the sediment and bacterial mat biotopes. There were pronounced differences in OTU richness and evenness among clusters and also considerable variation among certain host species within clusters. Additionally, the relative abundance of some prokaryotic taxa also differed among clusters with Poribacteria, e.g., being recorded in all sponge species, but with very low relative abundances in species of two of the three clusters. This sponge-associated phylum was, however, recorded at relatively high mean abundance in bacterial mat samples, which also housed relatively high abundances of actinobacterial and Chloroflexi members. Our results support high microbial abundance (HMA) status of the species Aaptos lobata, Hyrtios erectus, Pseudoceratina purpurea and Xestospongia testudinaria and low microbial abundance (LMA) status of the species Acanthella cavernosa, Echinodictyum asperum, Jaspis splendens, Ptilocaulis spiculifer, Stylissa carteri and Suberites diversicolor. Other species (Agelas cavernosa, Agelas nemoechinata, Acanthostylotella cornuta, Paratetilla sp., Hymeniacidon sp. and Haliclona cymaeformis) deviated somewhat from the typical HMA/LMA dichotomy and formed a strongly supported cluster., (© FEMS 2019.)

Much recent marine microbial research has focused on sponges, but very little is known about how the sponge microbiome fits in the greater coral reef microbial metacommunity. Here, we present an extensive survey of the prokaryote communities of a wide range of biotopes from Indo-Pacific coral reef environments. We find a large variation in operational taxonomic unit (OTU) richness, with algae, chitons, stony corals and sea cucumbers housing the most diverse prokaryote communities. These biotopes share a higher percentage and number of OTUs with sediment and are particularly enriched in members of the phylum Planctomycetes. Despite having lower OTU richness, sponges share the greatest percentage (>90%) of OTUs with >100 sequences with the environment (sediment and/or seawater) although there is considerable variation among sponge species. Our results, furthermore, highlight that prokaryote microorganisms are shared among multiple coral reef biotopes, and that, although compositionally distinct, the sponge prokaryote community does not appear to be as sponge-specific as previously thought.