Deep in the ocean, brown algae and diatoms produce a complex carbohydrate molecule called fucoidan, which helps form the algae's protective outer layer. The fucoidan molecule is very difficult for microbes to break down because its chemical structure may include dozens of different linkages and branching patterns that vary from one algae species to another. This resistance to decay is one reason why fucoidan matters; when microbes struggle to break it down, fucoidan can sink deep into the ocean, carrying carbon with it and potentially storing it for long periods. This could make fucoidan an important player in the ocean’s carbon cycle.For many years, scientists knew of individual bacteria th...