Production and ecological function of fucoidans from marine algae in a changing ocean

Fucoidans have multiple biological and biomedical functions, e.g., antibacterial, antiviral, immunomodulatory, inflammatory, and growth-promoting effects. Recent studies show that they also have essential ecological functions whereas our understanding in this field is very superficial. This study first reviewed the fucoidan content in algae and the highest content of 13.3 % in Undaria pinnatifida sporophyll and the lowest content of 0.1 % in Alaria angusta were found. Field investigation demonstrates that light, temperature, salinity, and nutrient can affect fucoidan production in algae; while more laboratory experiments need to be carried out to verify these conclusions. Brown algae can excrete 8-31 % of their net carbon fixation into seawater in the form of fucoidans. Fucoidans are highly recalcitrant to bacterial degradation, enabling the carbon within them to be stored for centuries. Therefore, fucoidans can play an essential role in carbon sequestration. Ocean afforestation with brown algae may be an effective approach to remove atmospheric CO₂ since fucoidans have a high carbon content while seldom need any nitrogen or phosphorus. Fucoidan production in a warming and CO₂ enriched ocean was also discussed. This study provides new insight into production and ecological functions of fucoidans, indicating their role in carbon sequestration and climate change alleviation.