Marine Macrophytes as Macromolecular Resources in the Mediterranean Circular Bioeconomy: Ecology, Green Ex-Traction, Bioactivity, and Valorization of Posidonia oceanica, Padina pavonica, and Chaetomorpha linum

Abstract

Marine macrophytes are major components of Mediterranean coastal ecosystems and potential sources of renewable macromolecules, functional extracts, and structural materials. This review critically compares three taxonomically and chemically distinct biomasses: the endemic seagrass Posidonia oceanica, the calcified brown macroalga Padina pavonica, and the filamentous green macroalga Chaetomorpha linum. Their ecological functions and biomass-generation pathways are distinguished because beach-cast seagrass leaves, seasonally detached macroalgae, and biomass removed from eutrophic lagoons cannot be treated as equivalent feedstocks. The review examines green extraction technologies, principal macromolecular and bioactive fractions, biological activities, and application pathways in remediation, agriculture, cosmetics, nutraceuticals, packaging, composites, and construction. Particular attention is given to feedstock heterogeneity, contaminant control, evidence strength, standardization, ecological sourcing, and translational readiness. Comparative analysis identifies P. oceanica primarily as a lignocellulosic and fibrous platform, P. pavonica as a source of brown-algal polysaccharides and phlorotannins, and C. linum as a nutrient-recovery biomass with promising extractive and agronomic applications. The most credible development route is a species-specific cascading biorefinery supported by standardized feedstocks, real-world validation, regulatory planning, and integrated techno-economic and life-cycle assessment.