Underwater measurements of carbon dioxide evolution in marine plant communities: A new method

We developed a new methodology to determine CO2 fluxes in intertidal and shallow subtidal plant communities, namely seagrasses, both when the plants are submerged and when they are air-exposed. The apparatus comprises closed incubation chambers and a gas exchange column, designed to remove carbon dioxide from the water. Different types of incubation chambers were designed and built to adapt the system to distinct environments and incubation requirements. The methodology was tested under a comprehensive range of situations and its advantages and limitations are discussed. Overall, the method provides precise measurements of community carbon dioxide fluxes, through a fast and nonintrusive process, allowing repeatable in situ measurements of carbon uptake both in submerged and airexposed conditions. As the experimental apparatus is identical, directly comparable measurements of air-exposed and submerged community production may be obtained, allowing sound estimates of daily carbon budgets of intertidal and shallow subtidal communities.