CO2 sequestration by the marine planktonic microalgae Nannochl-oropsis salina and Isochrysis galbana as well as macroforms Gracilaria corticata, Sargassum polycystum and Ulva lactuca was estimated under laboratory conditions. The green seaweed U. lactuca registered 100% utilization of CO2 towards carbon fixation from the ambient water up to 15 mg/l and beyond that it declined to 60%. The microalgae were able to utilize 27.7% of dissolved CO2 at 15 mg/l, but did not show any effect either for carbon fixation or for emission at lower and higher levels. Gross primary productivity of these algae were also not affected by increase in the CO2 levels. It is estimated that the seaweed biomass along the Indian coast is capable of utilizing 9052 tCO2/d against emission of 365 tCO2 /d indicating a net carbon credit of 8687 t/d.

Carbon sequestration, microalgae, seaweeds, carbon credits