Why are seagrasses important?
1-Ecological contribution
Primary production: They produce more vegetal matter than tropical forests.
Source of food: They are at the base of numerous food chains.
Biodiversity hot spots: They provide shelter to several hundred of macro-invertebrates, and algae.
Water oxygenation: They generate over 10 litre of oxygen per m2 per day.
Protection from predators: They offer a refuge beneath the foliar shoots.
2-Sedimentary contribution
Reduction of water movement: They reduce wave and current force.
Stabilization of soft bottoms: They trap and fix sediment.
Fight against erosion in beaches: They function as barriers in the littoral zone due to the accumulation of dead leaves.
3-Economic contribution
Spawning areas and nurseries: They promote the reproduction of fish and crustaceans.
Habitats for numerous species: They provide shelter for economically important fish thus allow sustainable fishing activities.

Why do seagrass beds disappear?
1- Coastal development
They are threatened by port facilities, recreational activities and pollution.
2- Urban and industrial waste
Due to domestic/industrial discharges they can’t utilize light in the water column for photosynthesis.
3- Mechanical damage
Their rhizomes are removed from sediment by fishermen’s trawls and boat anchors.
4-Nutrient increase
They compete with epiphytic algae covering their leaves caused by nutrient increases from fish farming, agriculture and urban activity.

Studied seagrass beds on the Turkish coast
Mediterranean coastline, Turkey presents convenient conditions for the development of large seagrass beds.
Studies done at the Gökçeada Island and Mersin Area, in collaboration with the Istanbul University Fisheries Faculty, and the Middle East Technical University Institute of Marine Sciences respectively, confirmed the importance of these meadows.

The Mersin area has a particular importance as it corresponds to the limit of North-Eastern extension of the Posidonia meadows in the Mediterranean Sea. This geographical limit of extension of the species seems related to a too high water temperature during summer season.
Whereas the meadows in Gökçeada Island seem to be under the influence of water masses from the Black Sea (low water salinity) and Mediterranean Sea (high water salinity).

Action Plan for the Conservation of Marine Vegetation in the Mediterranean Sea
Adopted in 1999, by the Contracting Parties to the Barcelona Convention, this Action Plan has several objectives:
*To implement measures for the management and protection of marine plant species
*To fight against the destruction of these formations, accepted to be key components of littoral ecosystems
*To ensure the preservation of these formations in characteristic areas.
The implementation of this Action Plan has been entrusted to the Regional Activity Centre for Specially Protected Areas (UNEP/MAP-RAC/SPA).

The MedPosidonia Project
In the framework of this Action Plan, a sub-regional project for the inventorying, mapping and monitoring of Posidonia meadows in Algeria, Libya, Tunisia and Turkey (MedPosidonia Project) has been implemented over a three-year period (2006-2008), thanks to the financial support of the Total corporate Foundation.
The Project aims at collecting information on the presence and evolution of Posidonia meadows in selected sites, and training national teams to make them able to pursue these tasks in the future.

Posidonia oceanica (Linnaeus) Delile

Common names: Seagrass (En), Deniz çayırı (Tr)
Distribution: An endemic marine phanerogame of the Mediterranean and Aegean Seas.
Habitat: It forms extensive beds in the infralittoral bottom of the basin. Most commonly on mobile and soft substrates, such as coarse sand, sometimes mixed with mud, but also on rocky sea bottoms. The plant needs strong light. The two limiting factors fort the growth of P. oceanica are transperancy of water and depth. These extend from the surface to depths of around 30-35 meters, reaching 40 meters (according to water limpidity) in particularly clear water. It is stenohaline (tolerance regarding salinity) and disappears near river mouths and is completely absent in freshwater areas. Broken leaves of this seagrass may form brownish soft balls (sea-balls), when mixed with sand grains and rolled by the waves.
Life history: The primary mechanism of reproduction is vegetative from perennial rhizomes. Flowering and fruiting is considered uncommon.
Dimension: Leaves are norrow and flat and about 1 cm width and 30 cm or more in length.
Morphology: P. oceanica is one of the most important primary producer in the Aegean and Mediterranean Seas. It is organized in roots a stem named rhizome and leaves. The rhizomes are developed horizontally and vertically. Posidonia meadows are considered as the most important ecosystems along the coasts. It forms a suitable substrate and shelter area for other macro and microalgae and it constitutes a habitat for many other species. It is the main biodiversity reservoir in the Mediterranean (with the Coralligenous community); the meadows weaken the hydrodynamic force (waves swell). This species is under protection by law in Turkish waters. However, they are declining due to coastal infrastructure; bottom trawling, beach set net, gill nets, anchoring, turbidity, and pollution. Because of the particular importance of Posidonia meadows in the Mediterranean, their conservation is considered one of the main priorities of the present Action Plan.

References

Öztürk, B., Aktan, Y.,Topaloğlu, B., Keskin, Ç., Karakulak, S., Öztürk, A.A., Dede, A., Türkozan, O. (2004). Marine Life of Turkey in the Aegean & Mediterranean Seas (ed., B. Öztürk). Turkish Marine Research Foundation (TÜDAV) Publications. Marine Education series. Number 10. İstanbul, Turkey. 200pp.

http://www.rac-spa.org/medposidonia