Posidonia oceanica 

Scope: Global & Mediterranean
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Liliopsida Alismatales Posidoniaceae

Scientific Name: Posidonia oceanica (L.) Delile
Common Name(s):
English Neptune Grass, Mediterranean Tapeweed, Neptune Grass, Species code: Po
Alga oceanica (L.) Kuntze
Zostera oceanica L.
Taxonomic Source(s): The Plant List. 2015. The Plant List. Version 1.1. Available at:

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2016
Date Assessed: 2013-07-15
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.
Facilitator/Compiler(s): Numa, C.
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:

Geographic Range [top]

Range Description:

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).

Countries occurrence:
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
Additional data:
Estimated area of occupancy (AOO) - km2:12300Continuing decline in area of occupancy (AOO):Yes
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:3000000
Continuing decline in extent of occurrence (EOO):YesExtreme fluctuations in extent of occurrence (EOO):No
Extreme fluctuations in the number of locations:No
Lower depth limit (metres):45
Upper depth limit (metres):1
Range Map:Click here to open the map viewer and explore range.

Population [top]

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. 
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:No
All individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:

This species forms commonly monospecific meadows from the intertidal to maximum depths of 45 m although can also be found forming mixed meadows. It is common on different substrates and habitats, from rocks to sandy bottoms (Bethoux and Copin-Motegut 1986), with the exception of estuaries where the input of fresh water and fine sediments is too high for its growth.

Posidonia oceanica is a large, long-living but very slow-growing seagrass. Its shoots, which are able to live for at least 30 years, are produced at a slow rate from rhizomes which grow horizontally at a rate of a few centimetres each year. Over centuries, the rhizomes form mats which rise up into reefs that help to trap sediment and mediate the motion of waves, thus clarifying water turbidity and protecting beaches from erosion (Boudouresque et al. 2012). The accumulation of Posidonia oceanica debris (berms) on the beaches provides also very effective protection against coastal erosion (Pergent et al. 2012).

Posidonia oceanica is a monoecious species, that is, male and female flowers are produced in the same inflorescence. Its biological characteristics with rare sexual reproduction and slow horizontal growth of rhizome edges, however, don’t provide a rapid recolonization of degraded or new forming beds (Meinesz et al. 1991).

It is an important habitat-forming species and provides habitat for many species. Nursery grounds for the juveniles of many commercially important fishes and vertebrates, such as for several species of the family Sparidae (for example, Diplodus annularis), Serranidae (for example, Serranus cabrilla), Labridae (for example, Coris julis and Crenilabrus maculatus) and Scorpaenidae (for example, Scorpaena scrofa and Scorpaena porcus), as well as the sea urchin Paracentrotus lividus. Posidonia oceanica is also grazed by the green sea turtle (Chelonia mydas) and the fish Sarpa salpa (Thomas et al. 2005).

The resilience of Posidonia oceanica and the meadows it creates seems to be relatively high (Pergent et al. 2012). It is relatively strong to seawater temperature variations and the invasion by alien species, although it seems weaker to slightly salinity fluctuations, turbidity and the increase of sedimentation rate (Pergent et al. 2012).

Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):35

Use and Trade [top]

Use and Trade:  Posidonia oceanica was used for animal food, especially for poultry, sometimes for camels during famines. The dead leaves are used in mattresses and pillows and for some other anecdotal uses (toys).  It also is used in charcoal processing, compost, and as substrate for hydroponic agriculture and organic enrichment, and roof insulation. Posidonia oceanica banquette or beach wrack is currently used for building insulation Europe.

Threats [top]

Major Threat(s): Posidonia oceanica is threatened at depth by mechanical damage from trawling, boat anchoring, and turbidity. Coastal development including shoreline hardening, urban and harbour infrastructure, and sand mining affect the upper limit of Posidonia meadows.

Eutrophication (originated from the discharges of agriculture nutrients, organic matter, aquaculture and urban waste) and pollution, especially in coastal regions that are heavily populated, are a problem in many coastal areas. Invasive macroalgae such as Caulerpa taxifolia and Caulerpa racemosa can grow on Posidonia rhizomes and sand and their proliferation could degrade sediment quality and accelerate the decline of the meadow (Marbá and Duarte 2010). The proliferation of other epiphytic invasive species, such as Lophocladia lamellandii in the western Mediterranean can also threaten the survival and affect the density and complexity of the communities in the meadow. Climate change would be an additional threat through the warming of waters, sea level rise and extreme weather events (Pergent et al. 2012).

The accumulation of some of these factors with the lack of genetic variability and slow growth, makes Posidonia oceanica less resilient to disturbance.

Regression of the meadows is often related to the impact of human activities, but meadows of Posidonia oceanica also seem to decline in areas where anthropogenic pressures are very low, indicating that other climatic or biological factors are taken part (Boudouresque et al. 2009).

Conservation Actions [top]

Conservation Actions:

Posidonia oceanica is protected by EU legislation (Habitat Directive), the Bern and Barcelona Conventions and some national legislations. EU fishing regulations limit trawling activities near the shore (either above 50 m or a certain distance from the coast), which constitute an indirect protection measure for the species (EC Council Regulation No. 1967, 21/12/2006). Posidonia oceanica is also protected in various marine protected areas in the countries along the Mediterranean Sea (UNEP-MAP-RAC/SPA 2009).

Efforts have been made to prevent physical damage caused by trawler-fishing on the meadows by placing artificial reefs along some stretches of the coast, and also by mounting a coastal watch to prevent illegal trawling.

At the Mediterranean level, Posidonia oceanica is included in the Barcelona Convention Annex II (list of endangered or threatened species). The species is also included in the Annex I (Strictly Protected Flora Species) of the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention).

In Albania, seagrass meadows are protected in the national legal framework by a Decision of the Council of Ministers on protected species (UNEP-MAP-RAC/SPA 2007).

In Croatia, Posidonia oceanica is a nationally protected species by the ordinance on “Proclamation of Wild Taxa as Protected or Strictly Protected” (Official Gazette no. 7/2006) (UNEP-MAP RAC/SPA 2007).

In France, legal protection of Posidonia oceanica comes under the Law of 10 July 1976 on nature protection, and its Implementing Decree of 25 November 1977 concerning the protection of the wild flora and fauna of the French natural heritage (Journal Officiel of 9 August 1988; Boudouresque et al. 2012).

It is also nationally protected in Italy by the law no.175, dated 27 May 1999. Furthermore, the Ligurian region passed in 2001 an EIA regulation for physical planning projects in Site of Community Interest (Habitat Directive) which include many Posidonia oceanica habitats (Deliberazione di Giunta Regionale no. 646, dated of 8 June 2001). They also developed regulations to assess the conservation status and degree of impact of different coastal development on the meadows (Deliberazione di Giunta Regionale no. 773 of 2003; Deliberazione di Giunta Regionale no. 1533 of 2005, respectively).

In Montenegro, Posidonia oceanica is protected by the national legislation as rare or endangered species. The meadows are also protected from trawling by a national fisheries ban (trawling is forbidden above depth of 50 m and in less than two nautical miles from the coast) (National Gazette 55/03).

In Slovenia, Posidonia oceanica is listed in the government decree as a rare and endangered species since 2002. In Turkey, it is also protected at the national level by the “Circular on sea and inland waters no. 37/1".

In Spain, the species is included in the Life of Wildlife Species (R.D.139/2011 no. 46). Furthermore, the governments of some autonomous regions, like Catalonia, Valencia and the Balearic Islands, have established regulations to protect this and other seagrass species. In Catalonia’s case, an Order dated 31 July 1991 (DOGC no. 1479 12/08 / 91) includes the protection of Posidonia oceanica prohibiting the destruction, sale, purchase or use of this species. In the Region of Valencia, it is also prohibited the destruction of seagrass meadows because these are areas of fishing importance (DOGV no. 1724, of 14/02/92). The government of the Balearic Islands, through an Order dated 21 September 2991, regulates any fishing, shellfishing and aquaculture activities to be conducted on or above seagrass meadows.

In Turkey, Posidonia meadows are also protected in the national legal framework by the “Circular on sea and inland waters n°37/1" (UNEP-MAP-RAC/SPA 2007).

Errata [top]

Errata reason: An errata assessment was created to correct the distribution map as an incorrect map was originally published.

Citation: Pergent, G., Gerakaris, V., Sghaier, Y.R., Zakhama-Sraier, R., Fernández Torquemada, Y. & Pergent-Martini, C. 2016. Posidonia oceanica (errata version published in 2017). The IUCN Red List of Threatened Species 2016: e.T153534A118118072. . Downloaded on 21 September 2018.
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