BiodiversityShapes the Climate Value of MacroalgalSystems

Abstract Biodiversity is central to the functioning, stability, and climate relevance of marine vegetated ecosystems, yet its role in macroalgal carbon sequestration remains underappreciated in current climate and biodiversity frameworks. Macroalgae contribute substantially to coastal primary production, habitat formation, and nutrient cycling, while supporting diverse ecological communities across temperate, tropical, and polar seas. However, their environmental value extends beyond that of carbon capture alone. In biologically diverse macroalgal systems, modulated biodiversity can also help control toxic materials arising from anthropogenic activities, including CO2, SOx, and NOx, by integrating these pollutants into existing elemental biogeochemical cycles and enabling their transformation into more benign and potentially useful chemical forms. In this review, we examine macroalgal biodiversity as a determinant of marine carbon sequestration potential across natural ecosystems, restoration efforts, and cultivated systems. We synthesize current understanding of how taxonomic and functional diversity influence carbon fixation, biomass stability, trophic transfer, detrital export, nutrient retention, pollutant buffering, and resistance to environmental stress. We further assess key uncertainties surrounding carbon permanence, ecological trade-offs, measurement, reporting, and verification, and the risks associated with simplified or monoculture-based deployment strategies. We argue that biodiversity should be treated not merely as a cobenefit of macroalgal systems but as a central design principle for evaluating their ecological performance, climate relevance, and broader capacity to restore biogeochemical balance in anthropogenically stressed environments.