Marine sponges are well known for their associations with highly diverse, yet very specific and often highly similar microbiota. The aim of this study was to identify potential bacterial sub-populations in relation to sponge phylogeny and sampling sites and to define the core bacterial community. 16S ribosomal RNA gene amplicon pyrosequencing was applied to 32 sponge species from eight locations around the world's oceans, thereby generating 2567 operational taxonomic units (OTUs at the 97% sequence similarity level) in total and up to 364 different OTUs per sponge species. The taxonomic richness detected in this study comprised 25 bacterial phyla with Proteobacteria, Chloroflexi and Poribacteria being most diverse in sponges. Among these phyla were nine candidate phyla, six of them found for the first time in sponges. Similarity comparison of bacterial communities revealed no correlation with host phylogeny but a tropical sub-population in that tropical sponges have more similar bacterial communities to each other than to subtropical sponges. A minimal core bacterial community consisting of very few OTUs (97%, 95% and 90%) was found. These microbes have a global distribution and are probably acquired via environmental transmission. In contrast, a large species-specific bacterial community was detected, which is represented by OTUs present in only a single sponge species. The species-specific bacterial community is probably mainly vertically transmitted. It is proposed that different sponges contain different bacterial species, however, these bacteria are still closely related to each other explaining the observed similarity of bacterial communities in sponges in this and previous studies. This global analysis represents the most comprehensive study of bacterial symbionts in sponges to date and provides novel insights into the complex structure of these unique associations.

Marine sponges (phylum Porifera) are a diverse, phylogenetically deep-branching clade known for forming intimate partnerships with complex communities of microorganisms. To date, 16S rRNA gene sequencing studies have largely utilised different extraction and amplification methodologies to target the microbial communities of a limited number of sponge species, severely limiting comparative analyses of sponge microbial diversity and structure. Here, we provide an extensive and standardised dataset that will facilitate sponge microbiome comparisons across large spatial, temporal, and environmental scales. Samples from marine sponges (n = 3569 specimens), seawater (n = 370), marine sediments (n = 65) and other environments (n = 29) were collected from different locations across the globe. This dataset incorporates at least 268 different sponge species, including several yet unidentified taxa. The V4 region of the 16S rRNA gene was amplified and sequenced from extracted DNA using standardised procedures. Raw sequences (total of 1.1 billion sequences) were processed and clustered with (i) a standard protocol using QIIME closed-reference picking resulting in 39 543 operational taxonomic units (OTU) at 97% sequence identity, (ii) a de novo clustering using Mothur resulting in 518 246 OTUs, and (iii) a new high-resolution Deblur protocol resulting in 83 908 unique bacterial sequences. Abundance tables, representative sequences, taxonomic classifications, and metadata are provided. This dataset represents a comprehensive resource of sponge-associated microbial communities based on 16S rRNA gene sequences that can be used to address overarching hypotheses regarding host-associated prokaryotes, including host specificity, convergent evolution, environmental drivers of microbiome structure, and the sponge-associated rare biosphere.

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Summary In order to understand physiological, ecological and biological processes, it is often crucial to determine an organism's volume and surface area (SA). Most of the available methods require sacrificing the organism or at least removing it from its natural habitat, in order to measure these parameters. Advances in computer vision algorithms now allow us to determine these parameters using non‐destructive, three‐dimensional modelling. The addition of cloud computing and the availability of freeware make this tool widely accessible. Photographs of corals and sponges were taken in natura and used to create digital 3D models using the ‘structure‐from‐motion’ technique. Modelling was done online using 123D Catch freeware (Autodesk Inc.). Volume and SA of the corals and sponges were calculated from these 3D models. Comparing in situ 3D modelling to current measuring methods (e.g. water displacement, paraffin dipping) showed that volume calculation by 3D modelling gave fast results accurate to within 8% of estimated true volume. Using cloud computing enabled the creation of a 3D model in <30 min. SA accuracy was found to differ significantly, depending on the shape of the modelled object, with an accuracy ranging widely from 2% to 18%. We found that in situ volume and SA measurements created by 3D modelling enable easy, fast and non‐intrusive studies of benthic aquatic organisms, without removing the subject organisms from their habitat, thus enabling continuous study of natural growth over extended time periods. The freely available freeware, along with ease of use, makes this method accessible to many areas of research.