Ecological role
Posidonia oceanica absorbs and sequesters carbon dioxide (41,500,000 kg in total per year) by the same process as terrestrial chlorophyll plants (photosynthesis) and produces a large amount of oxygen (1 m² of seagrass produces 10 to 14 litres of oxygen per 24 hours).
Moreover, the dead leaves and aegagropiles[1] of the meadow washed up on the shore also retain heat and humidity.
Posidonia oceanica therefore contributes to the reduction of the greenhouse effect (Fig.11) and thus to the fight against global warming.
[1] Fibrous remains of the rhizomes which, when torn out, agglomerate under the effect of the currents with the remains of the leaves and scales.
Figure 9. Internet Geography Greenhouse Effect
To prove that Posidonia oceanica absorbs Co2 and releases O2, and that its dead leaves and aegagropiles retain heat, we realized two experiments.
Click here to read the report on the experiment on Co2 absorption and O2 release by Posidonia oceanica
Click here to read the report of the experiment on heat capture by dead leaves and aegagropiles of Posidonia oceanica.
Posidonia oceanica produces a large quantity of plant matter and thus remains an essential link in the food chain (Fig. 10) .
Indeed, thanks to its leaves and the epiphytes growing on them, the Posidonia oceanica meadow provides an important part of the primary benthic production (Ramzi Sghaier, 2013).
This biomass is then either: 1. stored in the matte; 2. assimilated by detritus feeders (micro-organisms, crustaceans, etc.); or 3. exported to other ecosystems (shores, sea bed, etc.) in the form of dead leaves.
It should be noted that these plant materials are very rarely consumed by herbivores as they are degraded by detritivores which are then consumed by other species.
Figure 10. Fate of primary production (as a percentage of carbon) of Posidonia oceanica. Primary production of epiphytes is not considered here. According to G. Pergent (original)
Finally, Posidonia oceanica is a major centre of biodiversity.
Indeed, this meadow is a spawning ground, a nursery and a permanent habitat for many species (Fig. 11) (more than 400 different species of plants and several thousand animal species inhabit Posidonia oceanica meadows).
Figure 11. Ecological role of the Posidonia oceanica meadow (according to J.G. Harmelin 1993; M-A. Mateo)