Posidonia herbarium
Native to the Mediterranean, the Posidonia seagrass meadows cover an area of more than 2 million hectares along the coasts. This underwater forest of high ecological interest is threatened by global warming and by boat anchors near the coasts. VIDEOGRAPHIC
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00:00Native to the Mediterranean, the Posidonia seagrass meadows cover an area of more than
00:122 million hectares along the coasts.
00:14The leaves can reach up to a metre high.
00:17They provide shelter and a place to reproduce for fish, which feed on the small invertebrates
00:21which live there, such as worms and shrimp-like crustaceans.
00:25The Posidonia seagrass meadows also protect the coast from erosion by breaking the swell
00:30and forming a covering on the beaches where it accumulates in winter.
00:34This underwater forest also absorbs carbon, which helps to reduce greenhouse gases causing
00:39climate change.
00:40Carbon, which is absorbed in the leaves via photosynthesis, travels to the roots and the
00:45rhizomes, as do the sediments floating in the ocean.
00:49The seagrass roots and sediments form a dense mattress which can become several metres thick
00:54and hold carbon for thousands of years.
00:57For the same amount of surface area, the seagrass meadows absorb more carbon than a tropical
01:02rainforest.
01:04But the Posidonia seagrass meadows are threatened by the heating of the oceans and are damaged
01:09by boat anchors near the coast.
01:11Scientists fear that the degradation of the seagrasses could result in the release of
01:15the large amounts of carbon they contain into the atmosphere.
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