|Scope: Global & Mediterranean|
|Scientific Name:||Posidonia oceanica (L.) Delile|
Alga oceanica (L.) Kuntze
Zostera oceanica L.
|Taxonomic Source(s):||The Plant List. 2015. The Plant List. Version 1.1. Available at: http://www.theplantlist.org/.|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Pergent, G., Gerakaris, V., Sghaier, Y.R., Zakhama-Sraier, R., Fernández Torquemada, Y. & Pergent-Martini, C.|
|Reviewer(s):||Short, F.T., Otero Villanueva, M., Semroud, R. & Buia, M.|
|Contributor(s):||Panayotidis, P., Ruiz, J. & Yücel Gier, G.|
Posidonia oceanica is endemic to the Mediterranean Sea, and is the most widespread seagrass species in the region. It is an important habitat forming species and provides habitat for many species. There have been declines in the population of P. oceanica due to mechanical damage from trawling and boat anchoring, coastal development, and eutrophication and other forms of pollution, with losses particularly observed in the western and northern Mediterranean. The overall decline in the Mediterranean has been measured as approximately 10% over the last 100 years (Pergent et al. 2009) but recent analysis of area coverage indicates 34% of decline in distribution area or degradation in the last 50 years (Telesca et al. 2015). Further information is needed. P. oceanica is a very slow growing species and takes a long time to recolonize areas from where it has been removed, although there is some evidence that it has recolonized sites where it has been protected.
Estimations indicate that the area decreased between 1910 and 1965 of 5%, and since then to present time this percentage has increased to 34%. Assuming that the decreasing percentage in area coverage is equivalent to the decreasing in population, the estimated percentage of regression in three generation lengths (105 years) is estimated to be 39%. These data are based on the areas where historical information is available which mainly correspond to the Western Mediterranean basin. Here, the species could qualify as Vulnerable in one or two generation lengths if the threats are not reduced. Considering the current conservation actions in place however, the species should be considered as Near Threatened in the Western Mediterranean basin.
At global level this Mediterranean endemic species is listed as Least Concern in view of its extended AOO and EOO, the suspected stable populations in part of its range and the present conservation actions together with the recovery capacity of damaged meadows observed in some protected areas. More information on species distribution, and threats impact in the Eastern and Southern Mediterranean basin is needed.
|Previously published Red List assessments:|
Posidonia oceanica is present in the entire Mediterranean basin with the exception of large estuaries, and colder parts of the Mediterranean such as most of the Gulf of Lion, the northern part of the Adriatic and the westernmost part of the Alboran Sea close to the Gibraltar Strait. Moreover, its absence in the extreme southeast part of the basin seems to be directly related to the environmental conditions with very high water temperature during summer time (Celebi et al. 2006).
The species is also present along the east Aegean coast from Alanya province to the Dardanelles Strait and in the Marmara Sea of Turkey (Yüksek and Okus 2004, Meinesz et al. 2009).
The most extensive Posidonia oceanica meadows in the western Mediterranean can be found in France (Hyères and Giens bays and off the eastern coast of Corsica), Italy (western Sardinia and Sicily, especially) and several sites in Spain, though less extensive meadows can be found scattered across the region (Leonardini et al. 2008, Pergent-Martini et al. 2009). The species is abundant from the regions of northern Catalonia, Valencia, Murcia, the Balearic Islands, and down to Cabo de Gata (Almería) in the Andalusian region. Between Cabo de Gata and the Gibraltar Strait, Posidonia oceanica is only present at some localities, forming isolated patches, with “no true meadows” (Luque and Templado 2004).
Off the Ligurian coast of Italy, Posidonia oceanica meadows are found in the Island Ischia from the northern part of the Gulf of Naples (Green and Short 2003) and Capo Feto (southwest of Sicily) (Badalamenti et al. 2006). In the northern Ionian Sea, it forms isolated beds from ∼10 to 25 m in depth (Costantino et al. 2010). Rich meadows spread along the coasts of the southern Adriatic and northern Ionian Seas (Apulia region, southern Italy) and more isolated populations are found from Velipoja to Rodoni Promontory, and from Durresi to Vlora (Albanian coast).
Posidonia oceanica is widely distributed in the Aegean Sea. In Greece, Posidonia oceanica meadows can be found almost everywhere on the Greek coastline with the exception of the river mouths and the estuarine areas of the large rivers as Evros, Nestos, Strymonas, Aliakmonas, Axios as well as in some very isolated bays (Elefsis Bay, Saronikos Gulf). The population in the northern Adriatic is present in a small area between the towns of Koper and Izola at the Slovenian coast in the Gulf of Trieste (the northernmost part of the Adriatic). It is also found along the western coast of the Istria Peninsula in Croatia including the National Park of Brijuni (Jogan 1994). Also, Posidonia oceanica is present in other Croatian marine protected areas such as Telašćica, Natural Park of Lastovo Islands and National Park Mljet (Guala et al. 2012).
In the north Aegean Sea P. oceanica meadows can be found down to 25 m depth, in the gulfs (Alexandroupolis, Kavalla, Strymonikos, Kassadrian, Mount Athos, outer Thermaikos, Pagasitikos) and around the islands (Thasos, Limnos, northern Sporades, Lesvos). In the central Aegean Sea, P. oceanica meadows can be found down to 30 m depth, around the islands (Chios, Samos, Ikaria, Evoia) and in the gulfs (North and South Evoikos). In the south Aegean Sea P. oceanica meadows can be found down to 35m depth, in the Cyclades and, Dodecanese islands, Crete and in the gulfs (Saronikos, Argolikos, Lakonikos, Messiniakos). In the Ionian Sea P. oceanica meadows can be found down to 45 m depth, around the Ionian islands (Kerkyra, Lefkada, Paxoi, Ithaki, Kefallonia, Zakynthos) and almost in all western Greek coastline from Igoumenitsa – Messolongi (Ipeiros, Fokida), Patra - Methoni (Peloponissos) and Korinthiakos Gulf (Greek Ministry of Environment 2001, Gerakaris 2012, UNEP-MAP-RAC/SPA 2009b).
Posidonia oceanica meadows cover large areas the Montenegrin coastline extending to a maximum depth of 33 m (Buskovic et al. 2004).
Around Malta, the Malta-Comino Channel particularly, supports extensive meadows of Posidonia oceanica that in some places extend to a depth of around 43 m (Borg et al. 2006).
P. oceanica meadows cover large areas along the coasts of Turkey such as the Izmir region, the coast of Akkum (Sıgacık Bay, Aegean Sea), Edremit Bay, Kas and Kekova along the Lycian coast (WWF 2009), as well as in the Marmara Sea, the only place where there are found in a brackish environment (Dural et al. 2012, 2010, Meinesz et al. 2009, Albayrak et al. 2007). Here it occurs in the Dardanelles Strait and from Tekirdag in the North to the Gemlik Peninsula in the south of the Marmara Sea.
The species is rare on the Syrian coast, previously it was only is found at two localities: the northwest of Al Arwad islet and in the bay near Ras Ibn Hani (Mayhoub 1976) and its distribution is uncertain now. In contrast, nearby, the coast of Cyprus at the centre of the Levant Sea, sustains dense meadows. Dense stands of Posidonia oceanica and Cymodocea nodosa are common at different depths around the island of Cyprus (Green and Short 2003).
Posidonia oceanica meadows are also distributed in the majority of infralittoral and some mediolittoral zones of Libyan waters. mainly on the open sea but also around islands (Garah) and within the gulfs (Bumba, Ras Hilal and others) as well as within or at mouths of lagoons (Farwa) and at Ain Al Ghazala forming rare barrier reefs at 0.5-2 m (IUCN 2011).
In Tunisia, the species has a wide geographical distribution, particularly in the Gulf of Gabes and Gulf of Hammamet (INSTM/APAL 2003). Meadows are rarer in the Tunis Gulf although they form barrier reefs at Sidi Rais in the Cap-Bon region (El Asmi et al. 2003).
Posidonia oceanica has also been reported in many sites of Algeria (El Kala (Bebacha), Annaba, Taza, all the coast of Jijélienne in Oran, Faycel, Mostaganem coast, the island of Bounettah, Reghaia) (Lamouti and Gasmi pers. comm. 2010) and Morocco (Chafarinas Islands (Ya`fariyya) (Altamirano et al. 2010).
Native:Albania; Algeria; Croatia; Cyprus; Egypt (Egypt (African part)); France (Corsica, France (mainland)); Gibraltar; Greece (East Aegean Is., Greece (mainland), Kriti); Italy (Italy (mainland), Sardegna, Sicilia); Libya; Malta; Monaco; Montenegro; Morocco; Slovenia; Spain (Baleares, Spain (mainland)); Tunisia; Turkey (Turkey-in-Asia, Turkey-in-Europe)
|FAO Marine Fishing Areas:|
Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Posidonia oceanica is abundant in the Mediterranean, however there is evidence that the population is declining in the western Mediterranean. Several local studies have shown serious declines in P. oceanica meadows. However, accurate data are generally very localised and are lacking for many parts of the Mediterranean. Therefore, cases of observed regression are not representative of the region as a whole. Relatively healthy P. oceanica meadows, whose limits have changed little since the 1950s, can thrive in highly developed areas. In some areas, there is evidence of recolonization by P. oceanica after the human impact ceased or was reduced, but the process of recolonization is extremely slow, i.e. a few centimetres per year (Pergent-Martini et al. 1995).|
In several sites, the seagrass Cymodocea nodosa has taken advantage of the regression of this species to further its own development (Montefalcone et al. 2007). France has approximately 980 km2 of Posidonia oceanica meadows (Marine Protected Area Agency, unpublished). Massive regressions (44%), however, have been observed at several sites. Close to the city of Marseille, for example, meadows have deteriorated due to sewage disposal (Pergent-Martini et al. 1994). In Corsica (France), waste material dumped for 17 years from an asbestos quarry, caused the decline of 230 ha of Posidonia oceanica meadows in the vicinity (Pasqualini et al. 1999); 11.2 ha were lost and 9.8 ha were significantly degraded due to aquaculture activities (Ruiz et al. 2001).
Over last decade, most Spanish Posidonia meadows have been declining at a rate of 5% per year (Marbá and Duarte 2010). A retrospective demographic study also showed a similar trend between 1967 and 1992. In Murcia, Andalusia, Baleares and Valencia (Spain), this decline of meadows is not a widespread phenomenon and many are currently in relative good condition. However, clear regressions have been observed in some sites and at the depth distribution limit of the meadows due to illegal trawl fishing or other human related activities (Bernardeau-Esteller et al. 2010, Instituto de Ecología Litoral 2011, Consejería de Medio Ambiente 2010). Furthermore, in Catalonia (Spain), evident regressions have been observed in some locations and only 17% of them are believed to be in optimum condition (CRAM 2006-2007).
In the island of Agueli o Bounettah (Algeria), recent studies indicated a good general condition of the meadows (Lamouti and Gasmi 2010). In other North African countries such as Tunisia, Posidonia oceanica is in good condition in some sites while others show certain regression most due to anthropogenic coastal pressures (Zaouali and Ben Charrada 2010). In the Adriatic coast of Albania, Posidonia oceanica beds are rare, forming isolated beds around Rodeoni Cape, Porto Romano and Vlora Bay. The population along the Ionian coast from southwest Karaburuni Peninsula to the southern Albanian border (Sitllo Cape) is considered in good state (Beqiraj et al. 2008). By contrast, in the northern Ionian Sea, the spatial distribution seems to be more stable. Posidonia oceanica meadows covered about 330 km2 distributed along 320 km of coastline, mostly on the southern side of Apulia (Costantino et al. 2010).Recent analysis shows the estimated regression of Posidonia meadows amounted to 34% in the last 50 years (Telesca et al. 2015). This percentage is based on information where historical data are available which is equivalent to approximately 30% of the whole species distribution, most of it coming from the Western Mediterranean basin.