Marine algae play a key role in the global carbon cycle, converting CO₂ into organic matter. Much of this material is rapidly consumed, but a more resistant fraction, composed of complex algal glycans, remains as part of sequestered carbon. These glycans, which serve structural and defensive roles in algae, can also support specialized bacteria in the algal microbiome that have been largely overlooked. We hypothesize that specialized bacteria have co-evolved with algae and have a key role in unlocking glycans that maintain the algae microbiome and simultaneously modify the structure of glycans that participate in carbon sequestration processes. Bacteria belonging to the Verrucomicrobiota and Planctomycetota phyla are the only groups living on algae that carry the enzymes to consume these complex fucose-containing sulfated polysaccharides (FCPS). Using a combination of cutting-edge approaches (multi-omic, visualization, and physiologic examination), we will expand into the unknown diversity and population structure of FCSP-degrading bacteria on micro and macroalgae. Our ERC-funded project will investigate the interactions between these specialized bacteria and the algae that produce these complex sugars. Our goal is to reveal how these bacteria support algal health and examine the mechanisms that could play a role in carbon sequestration in marine environments.