Wada S. auteur aut IRD Kurosawa S. auteur aut IRD Agostini Sylvain auteur aut IRD Harvey B. auteur aut IRD Satoh Y. auteur aut IRD Milazzo M. auteur aut IRD Hall-Spencer J. M. auteur aut IRD text journalArticle eng text/pdf reformatted digital access Ocean acidification, driven by rising atmospheric carbon dioxide levels, has impacts on marine ecosystems. While elevated carbon dioxide concentrations have the potential to enhance Blue Carbon fixation and storage, the response of community photosynthesis in macroalgal-dominated ecosystems remains poorly understood. Here, we investigated the effects of elevated carbon dioxide on macroalgal communities using volcanic carbon dioxide vents as a natural analogue of ocean acidification. Net community photosynthesis was assessed using chambers positioned on the seafloor as well as water mass dynamics monitoring. Despite a shift in algal community composition, only minimal differences in net community photosynthesis were observed between reference and high carbon dioxide sites. The high carbon dioxide site had a lower abundance of algal species with carbon dioxide concentrating mechanisms, based on delta 13C isotope measurements. Carbon dioxide concentrating mechanisms facilitate photosynthesis under present-day levels of carbon dioxide in seawater, resulting in a negligible effect of elevated carbon dioxide on macroalgal community photosynthesis. These results challenge the assumption that ocean acidification will enhance Blue Carbon uptake and storage, necessitating a reevaluation of this perspective. specialized JAPON SHIKINE JIMA ILE 036 021 6 1 840 [8 p.] 2025 https://www.documentation.ird.fr/hor/fdi:010095461 10.1038/s43247-025-02730-2 [F B010095461] https://www.documentation.ird.fr/hor/fdi:010095461 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2025-12/010095461.pdf IRD - Base Horizon / Pleins textes 2025-12-10 2025-12-10 fdi:010095461 fre