Biodiversity of Mediterranean wetlands
The Mediterranean Basin is a world biodiversity hotspot, and its wetlands are veritable reservoirs of life.
Nearly 2,500 vertebrate species are found there and up to 10% of the world’s vascular plant species. Although wetlands cover only 2% of the total area of the region, one fourth of the species there depend on these habitats for their survival!
Yet, due to the threats weighing on Mediterranean wetlands, a third of these species are endangered.
Seagrass meadows are found on the interface between lagoons and the sea, where both types of environments merge.
In the intertidal zones, the vegetation is generally dominated by Zostera seagrass species, which usually give way to Ruppia species in the calmer, warmer more enclosed waters of saltwater lagoons. These two herbaceous plants are perennials and provide major spawning and feeding areas for coastal fish, and attract many herbivorous waterbirds.
Annual halophytic species that germinate during the dry season when the water goes back below ground level are found on the banks of seasonally flooded swampy areas. These plants include salicornia (Salicornia, Arthrocnemum) and the graminaceae in salt marshes that are resistant to both winter flooding and intense grazing.
Different Salicornia species cover vast areas of salt marshes in the Mediterranean Basin, particularly in the deltas, on the edge of lagoons, and around salt lakes in North Africa. They contribute to maintaining these structures by capturing sediments, which results in a characteristic landscape dotted with mounds.
Other halophytic plant communities grow on the edge of marshes such as rushes (Juncus spp.), which can form a belt that is several meters wide only around marshes, at the upper limit of the area that is flooded in winter, before tamarix (Tamarix spp.) gives way to wet meadows as we move away from the shore.
Rushes are among the most particular plant communities in the Mediterranean Basin. A great number of these highly diverse plants, and in particular several Isoetes species are only found in this region.
The large emergent plants of freshwater marshes
Phragmites australis reeds are clearly the dominant species among the large emergent plants found in freshwater marshes. This species grows in all places where it remains damp most of the year, and is found in floating masses in permanently flooded areas.
When there is intensive grazing, reeds can be replaced by rhizomatic grasses such as Aeluropus or Scirpus maritimus, which are more tolerant to salt and thrive in lightly grazed areas, often on the shores of deep lakes.
Sawgrasses (Cladium spp.) prefer permanently damp areas. They are rare in the Mediterranean Basin, and as papyrus are restricted to the eastern part of the basin. The largest stands are found in the Daimiel wetland in the centre of Spain and in the La Crau marsh in the Camargue.
Most riparian forests have disappeared from European floodplains, although in some deltas, some stands remain. Such is the case of Nestos, in Greece, where the last sixty hectares of a seasonally flooded forest of deciduous trees is located, and the Ebre Delta which hosts populations of poplars (Populus spp.), alders (Alnus spp.), and white willows (Salix alba).
Submerged and floating freshwater plants
Many species of submerged plants are different types of pondweed, like sago pondweed (Potamogeton pectinatus), which cover nearly one third of Lake Ichkeul in Tunisia, where it is the main species consumed by wintering duck populations. When the water is saltier, the pondweed gives way to wigeongrass, whereas in areas that remain dry for more than one month, there are shallow water communities such as stoneworts (Chara spp.), which can withstand the summer drydown.
The fresh and salt water lakes and marshes in the Mediterranean Basin are not only breeding and wintering sites for millions of birds, they also play a role as a stopover site for an even larger number of birds that feed and rest there during their annual migration between Africa and Northern Europe and Asia. The main migratory flyways skirt the Mediterranean Sea—to the east through Turkey and the Rift valley in Israel, and to the west through Morocco and Spain. Other more direct flyways cross the sea at the narrowest crossings, between Tunisia and southern Italy, via Malta, and between Libya and Greece and the Balkans, via Crete.
Mediterranean wetlands are a refuge for mammals that are poorly adapted to the hot, dry summers of the Mediterranean climate. Their undisturbed open areas are important habitats for animal species that have become rare such as the Iberian Lynx (Lynx pardinus) in Doñana in southern Spain). Some species such as the Southern Water Vole (Arvicola sapidus), water shrews, and beaver have also developed semi-aquatic adaptations.
Two thirds of the 120 amphibian species found in Mediterranean countries are endemic. Their conservation status is particularly preoccupying, and to some extent reflects the major degradation of their habitats (especially of temporary ponds). Reptiles are less well represented in wetlands, although several species of turtles and aquatic snakes can be found in them, while the crocodile has almost entirely disappeared.
The endemism of amphibians and reptiles is extremely high. Today’s fauna on Mediterranean islands is to a large extent the result of past connections between these islands and the European or African continent, but also the species introduced by people. On the islands in the western part of the Mediterranean Basin, endemicity rates for batrachians are high because their arrival dates back a long time, and they have a limited capacity to move. Whether it concerns new species, subspecies, or small, isolated populations, this range of genetic variation is very often the most highly threatened. Indeed, any modifications to the habitats of these species has irreversible consequences.
The freshwater fish fauna of the northern Mediterranean region is particularly remarkable in the Mediterranean Basin, with nearly 500 species, half of which (226 taxa) are endemic (128 species and 98 subspecies), in 13 families: the cyprinids, which are the most significant group of Gobius, the Cobitidae, Cyprinodontidae and Salmonidae, the Petromyzontidae, Acipenseridae, Siluridae, Percidae, Blennidae, Cottidae and Gasterosteidae. Most of these species live in plain rivers and natural lakes, to a lesser extent in mountain springs and brooks, and rarely in marshes, coastal lagoons, artificial canals, and reservoirs. The greatest diversity can be found in watercourses and natural lakes, with particularly significant areas of endemism on the Iberian Peninsula, in northern Italy, the Balkans, the Middle East, and western Morocco.Twenty species have already disappeared, and over 60% of endemic species are in some way threatened.