Among the five to eight additional core genera per diet, we only found genomes of the genera Roseobacter, Psychromonas (two genomes each), and Polaribacter (six genome) in the CAZy and SulfAtlas databases, and we searched for their algal polysaccharide degradation abilities (Fig. 4, Additional file 4: Table S3). Roseobacter (a genus only found associated with the two brown algal diets) shows a low capacity to degrade algal polysaccharides with only some secreted exo-glycosidases. Psychromonas (associated with the L. digitata and P. palmata diets) is likely able to degrade brown algal polysaccharides with several enzymes acting on extracellular oligosaccharides and a laminarinase from family GH16, but there was no sign of enzymes acting on red algal polysaccharides. All six genomes of the genus Polaribacter, associated with the P. palmata diet, contain enzymes acting on red algal polysaccharides, such as agar or porphyran (e.g., enzymes from families GH16, GH86, or GH117), or more specifically on carrageenans (P. sp. KT25b contains 2 iota-carrageenases from family GH82). Most of these genomes also encode enzymes able to degrade major algal cell wall polymers such as cellulose and hemicelluloses (e.g., presence of an endo-1,4-β-xylanase from family GH10, a GH39 xylosidase, and enzymes from families GH43, GH51, GH53, GH115, GH127).