Although the biochemical composition of algae is very different among algal groups, cellulose is a common material among many algal species. The process of cellulose biological degradation has been extensively studied in recent years. The mechanism of cellulose enzymatic hydrolysis by anaerobic bacteria is quite different from the mechanism of aerobic organisms. Anaerobic bacteria have a large multienzyme complex—cellulosome, which is attached to the cell envelope and consists of up to 11 different catalytic enzymes carried by scaffold-proteins [113, 114]. The enzy­matic hydrolysis of algal cellulose is relatively slow and can be inhibited by the close association with other structural materials, such as polyphenols, fucoidan, protein, and alginate. Therefore, other specie-specific sulphonated, methylated or carboxylated polysaccharides, mannitol, proteins, and lipids usually determine the more readily biodegradable fraction of algal biomass.