Dead matter

But what do the dynamics of carbon storage actually mean? “Above all, it’s a question of studying what is known as the ecosystem’s primary production”, Alberto Borges explains. “It’s the organic matter formed in a marine environment from carbon dioxide (CO₂) and the energy provided by light. In other words, this is the organic matter generated by photosynthesis, which involves the consumption of CO₂ and the production of oxygen. Part of the oxygen produced is consumed to ensure the respiration of the seagrass meadow”. In classic terms, the concentration of oxygen in the seagrass meadow increases during the day – i.e. photosynthesis occurs, which only takes place during the day because it needs light – and at night, this is where oxygen is consumed; this is why the ecosystem is said to 'breathe'. “In the summer, there is a maximum amount of organic matter in the seagrass meadow, as is the case in our gardens, owing to heat and light. But as autumn approaches, the leaves of the seagrass meadow start to fall, die and rot in the meadow to form what is known as litter, and to a lesser extent, the ‘matte’. The litter is exported out of the meadow”, the researcher continues, “but it’s in the matte that the carbon is stored for thousands of years: not in the living matter, but in the dead organic matter”. Therefore, the amount of matte, hence the storage of carbon, is directly linked to the amount of organic matter generated in the spring and summer (the primary production). As a result, measuring the variations in oxygen concentrations in the meadow all year round provides information on the status of its metabolism, i.e. the extent of its primary production on which the amount of dead matter, which allows the carbon to be stored, ultimately depends.