Sustainable production of ulvan from green macroalgae and its potential in carbon sequestration: A critical review

Ulvan, a sulfated polysaccharide abundant in green macroalgae, has emerged as a promising biopolymer due to its diverse biological activities. However, current understanding of its large-scale production pathways and ecological application potentials remains fragmented. This review synthesizes ulvan content in green seaweeds, revealing that it varies widely among species-ranging from very low to over 40 % of dry weight-and is significantly influenced by environmental factors such as temperature and light. We further analyze global biomass trends, noting a shift from wild harvest to aquaculture, alongside the immense and fluctuating biomass contributed by green tides, which represents a substantial yet underutilized source of ulvan. Crucially, we highlight ulvan's inherent resistance to bacterial degradation, which, combined with the massive biomass of green macroalgae in coastal ecosystems, underscores its significant but unexploited potential for long-term carbon sequestration. To balance economic feasibility and ecological sustainability, we propose an integrated framework for ulvan production and utilization. Offshore-grown macroalgae are prioritized for high-purity ulvan extraction to support the food and biomedical industries. Meanwhile, coastal algal biomass is leveraged for bioenergy production, with the resultant CO₂ sequestered in geological reservoirs. By synthesizing production dynamics and ecological synergies, this study provides novel insights into unlocking ulvan's potential as a sustainable biopolymer for blue bioeconomy and carbon-neutral initiatives.