In February 2012, after abalone had not been fed for a week, the most abundant phyla were Fusobacteria, Tenericutes, and Gammaproteobacteria (average of 72, 14, and 9% of all sequence reads per cage, respectively, Additional file 1: Figure S3). The phylum Fusobacteria was mostly composed of the genus Psychrilyobacter (99.9% of sequences in the phylum; 31% to 94% of all sequence reads per cage) and the phylum Tenericutes of Mycoplasma (99.9% of sequences in the phylum; 3–32% of all sequence reads per cage). The third most abundant taxonomic group, the class Gammaproteobacteria, was composed mainly of Vibrio (68% of sequence reads in the phylum; 1–23% of all sequence reads per sample). Other genera present in all cages represented 2% or less of the sequence reads per cage (Fig. 2). These global patterns validate the dominance of few genera in the abalone digestive microbiota at the starting point of the experiment.Fig. 2Relative abundance and taxonomical composition of abalone digestive microbiota at the genus level. Each panel represents the digestive bacterial community associated with feeding with Palmaria palmata (a), Laminaria digitata (b), Ulva lactuca (c), and Saccharina latissima (d). The taxonomical composition is represented for each cage triplicate over 1 year. Water temperature is indicated on the right side of each panel (values varying from 10 °C (blue) to 15 °C (red)). Less abundant genera: total number of sequence reads of these 651 genera for clearer representation in the figure. In c, the sample from cage U1 in January 2013 is missing. For unclassified genera, genera were assigned to the lowest taxonomic level identified. Verruc., Verrucomicrobiales; BD7-8, BD7-8 marine group; JTB255, JTB255 marine benthic group; OM60_clade, Alteromonadaceae OM60_clade; Gammap., Gammaproteobacteria; unc, unclassified