Additionally, a less abundant core microbiota was specific to at least a monospecific diet and contained aerobic genera: the Flavobacteriia Lutimonas, Ulvibacter, and Polaribacter; the Alphaproteobacteria Roseobacter and Pseudahrensia; the Gammaproteobacteria Psychromonas and Escherichia-Shigella; and the Verrucomicrobia Roseibacillus [52–59]. Notably, all members of this diet-specific and less abundant core microbiota, with the exception of Pseudahrensia, were identified during a phytoplankton bloom in temperate coastal waters in the North Sea . This suggests that these bacteria may not only be part of the epiphytic algal diet microbiota but could also be part of the bacterioplankton and be ingested along with the alga. For instance, members of the genera, Roseobacter, Ulvibacter, and Roseibacillus, were previously isolated from green and brown algae, and Roseobacter was found associated with the red alga Gracilaria vermiculophylla [19, 53, 55, 58]. Strains of Polaribacter and Psychromonas were previously found associated with Laminaria sp. and S. latissima, and both genera have members that can degrade red algal polysaccharides [54, 57, 60, 61]. Lutimonas and Pseudahrensia, however, were found only in marine invertebrates or seawater but not associated with algae [52, 56, 62–64]. The occurrence and maintenance over time of few diet- or plankton-derived specific bacteria suggests a selectivity of some genera, which could participate to the global functioning of the digestive gland in abalone. The remaining OTUs that are not part of the core microbiota are transient bacteria and represent a smaller fraction of the digestive microbiota over the year (up to 14% of sequence reads per cage). These rarer bacteria are probably ingested along with the algal diet and have either (i) died and left DNA remains in the digestive gland or (ii) survived the selection pressure and may participate in the algal recycling in the abalone digestive gland .