Seagrass beds (other than Posidonia) on Mediterranean infralittoral sand

Mediterranean seagrasses form dense and highly productive meadows or beds, between the surface to 15 m depth in coastal lagoons and down to 50 m depth in the open-sea, in clear water conditions. Besides the seagrass Posidonia oceanica, these meadows are built by several submerged magnoliophytes, such as: Cymodocea nodosa, Zostera marina, Zostera noltei or the introduced species Halophila stipulacea, and, in transitional waters and coastal lagoons by Ruppia sp. All these species can be found alone or combined among them to form mixed meadows. The basic physical requirements of seagrass meadows habitats are sufficient light, a suitable substratum (muddy or sandy bottom) and moderate levels of wave exposure. Their tolerance to variation of environmental factors (e.g. salinity, temperature, nutrient concentration) and their geographical distribution differ depending on the dominant seagrass species.

Seagrasses provide habitat for a large set of organisms. The leaf canopy and the network of rhizomes and roots provide substratum for attachment, and creates hiding places to avoid predation. As a result, the abundance and diversity of the fauna and flora living in seagrass meadows are consistently higher than those of adjacent unvegetated areas. In addition seagrass meadows play an important role as spawning zone and hatchery for several species of fishes and are wintering areas of several species of birds

Several sub-habitat can be distinguished. Cymodocea nodosa beds are widely distributed throughout the Mediterranean, and outside, around the Canary Islands and down the North African coast, and are usually frequent in areas with salinity fluctuations from 26 to 44%. These meadows are observed in coastal lagoons and in the open-sea. Eelgrass beds (Z. marina) are rare in the Mediterranean and it is found mostly as small isolated stands, down to 10-15 meters depth depending on water clarity. Dense meadows can however occur, especially, in coastal lagoons and transitional waters. They are distributed from the Arctic waters until the Mediterranean and are very abundant in the Baltic Sea, the North Sea and along the Atlantic coasts down to northern Spain. Ruppia beds grow in brackish waters, in permanent pools of mud or sand flats, as well as in inlets or estuaries. Mixed beds of Zostera and Ruppia can be observed in shallow sublittoral sediments. These communities are generally found in extremely sheltered bays and coastal lagoons, with very weak tidal currents.

Indicators of quality:

Extended seagrass beds with a good penetration to deep waters are characteristic of coastal waters with minimal anthropogenic impact. Since seagrasses are mostly perennial organisms, they reflect the temporally integrated environmental conditions, and, therefore, seagrasses are very good indicator on which environmental monitoring and management of coastal waters can focus. Cymodocea nodosa is considered at the Mediterranean level, as a biological quality element for the implementation of the Water Framework Directive and several indicators have been proposed for this assessment.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats