Carbon dioxide removal (CDR) potential in temperate macroalgal forests: A comparative study of chemical and biological net ecosystem production (NEP)

The carbon dioxide removal (CDR) capacity of macroalgae, a crucial component in climate regulation, has gained increasing attention. However, accurately estimating the CDR potential of macroalgae in natural conditions remains challenging, necessitating the use of multiple independent methods to reduce the uncertainties in these estimates. In this study, we compared two methods for estimating net ecosystem production (NEP), a key parameter in determining CDR potential: 1) NEP^Chem., derived from seawater carbonate chemistry and 2) NEP^Biol., based on photorespiratory measurements using benthic tent incubation. This study, conducted in a macroalgal forest dominated by Ecklonia cava, involved simultaneous measurements of NEP^Chem. and NEP^Biol. over a course of one year. Our findings revealed that NEP^Biol. was 1.23 times higher than NEP^Chem., with an annual rate of 3.69 tons CO₂ ha⁻¹ yr⁻¹. These results suggest that both independent methods are reliable and can be used complementarily to improve the accuracy of NEP measurements, thereby enhancing estimates of the CDR potential of macroalgae.