The living prokaryotic microbiome of the calcified geniculate (articulated) red alga, Corallina officinalis from the intertidal seashore is characterised for the first time based</p><p>on the V6 hypervariable region of 16S rRNA. Results revealed an extraordinary diversity of bacteria associated with the microbiome. Thirty-five prokaryotic phyla were</p><p>recovered, of which Proteobacteria, Cyanobacteria, Bacteroidetes, Actinobacteria, Planctomycetes, Acidobacteria, Verrucomicrobia, Firmicutes and Chloroflexi made up the</p><p>core microbiome. Unclassified sequences made up twenty-five percent of sequences suggesting insufficient sampling of the world’s oceans/macroalgae. The greatest diversity</p><p>in the microbiome was on the upper shore, followed by the lower shore then the middle shore, although the microbiome community composition did not vary between shore</p><p>levels. The C. officinalis core microbiome was broadly similar in composition to those reported in the literature for crustose coralline algae (CCAs) and free-living rhodoliths.</p><p>Differences in relative abundance of the phyla between the different types of calcified macroalgal species may relate to the intertidal versus subtidal habit of the taxa and</p><p>functionality of the microbiome components. The results indicate that much work is needed to identify prokaryotic taxa, and to determine the nature of the relationship of</p><p>the bacteria with the calcified host spatially, temporally and functionally.