The gut microbiota is of major importance for terrestrial herbivores; grinding and host enzymes are not sufficient for a complete digestion of plant material. Indeed, specific bacterial groups help degrade complex plant polysaccharides such as cellulose or starch (Bacteroidetes and Firmicutes in cow's rumen). In the marine world, herbivore digestion is still poorly understood. Red, green, and brown algae present a large array of complex polysaccharides for herbivores to digest. The abalone is a good study-case as it can digest these three algal groups but the role and fluctuations of the associated microbiota are poorly known. We thus investigated the effect of 4 algal diets (Palmaria palmata, Ulva lactuca, Saccharina latissima and Laminaria digitata) on abalone digestive microbiota on the Northwest coast of France over a year. Bacterial community composition from abalone digestive glands sampled every 2 months was explored using Illumina sequencing. Three bacterial genera dominated the community (86%-92%) for the whole year; the strictly anaerobic Psychrilyobacter, and facultatively anaerobic Mycoplasma and Vibrio. Their respective genomes showed their ability to ferment pyruvate but only Vibrio contained necessary enzymes for algal polysaccharide degradation, implying its role as a preliminary degrader. Diversity analyses showed specific seasonal patterns of the bacterial community according to algal diet. Communities associated to L. digitata and P. palmata diets seemed more stable over the year than those associated to S. latissima or U. lactuca. Altogether, in comparison to terrestrial herbivores, abalone presents a specific digestive microbiota, where diet-specific bacteria may assist in algal polysaccharide degradation.