Researchers studied the fate of the material produced by Posidonia seagrass meadows. This study, carried out in the Mediterranean Sea at STARESO, shows that the dead leaves of what is commonly known as Neptune grass accumulate in shallow areas, where they break down like a compost, remineralizing the organic matter. This has a previously underestimated effect on carbon fluxes in the Mediterranean coastal environments. Surprisingly, alongside this CO2 emission, oxygen production was also measured. This is linked to the presence of photosynthetic organisms living in this compost in the sea, which fundamentally differentiates it from compost on land.