Boundaries

This ecoregion extends from the Galician Atlantic coast (Finisterre Cape) in Spain to France’s south coast on the Mediterranean Sea.  The ecoregion is delimited largely by the Cantabrian Mountains, Pyrenees, Maritime Alps, and Cottian Alps. It includes northern Spain’s coastal drainages in the west, the Garonne-Adour-Dordogne drainages in the center, and the lower Rhône drainage in the east.

Topography

The landscape includes mountains, cliffs, plateaus, deeply incised valleys, glacial valleys, hills, broad river terraces, and flat alluvial plains. Elevations range from sea level to over 3000 m asl in the Pyrenees and Alps (Hijmans et al. 2004). Other high elevation areas include the Cantabrian Mountains, Basque Mountains, and Massif Central, which is an upland area that contains the largest concentration of extinct volcanoes in the world. Most of the Rhône basin is composed of alkaline rocks of Jurassic and Cretaceous sediments and Tertiary and Quaternary deposits (Olivier et al. 2009).

Freshwater habitats

The largest river in the ecoregion is the Rhône, its lower section from the Isère confluence to the Mediterranean Sea. Tributaries that drain into the lower Rhône section include the Isère, Drôme and Durance on its left bank and the Ardèche and Gard on its right bank. South of Lyon the river runs between the Massif Central and Alps with a gentle slope of 0.5 m/km. The river then widens as it crosses alluvial plains. Historically the lower Rhône was braided, with large sediment inputs from tributaries draining the Massif Central and Alps (Bravard 2010). High discharge from southern tributaries occurs in the fall and spring, with a majority of flooding occurring in September and October. The Rhône has a mean annual discharge of 1,720 m³/s at its mouth, supplying around 40% of the mean freshwater input into the Mediterranean Sea (Olivier et al. 2009). At Arles the river divides into the Grand Rhône and Petit Rhône. Between these two arms is the Camargue Delta (1450 km²). Composed of an extensive network of permanent and seasonal brackish lagoons, lakes, ponds, reedbeds, dunes, and marshes, it is the largest delta in Western Europe. To the west is another area of marshes, brackish lagoons, and ponds called the Petite Camargue on the right branch of the delta (Wetlands International 2002). It is followed by vast lagoons located along the Mediterranean Sea as far as the Pyrenees.

The Garonne is the third largest river basin in France, and includes the Lot, Tarn, Adour, and Dordogne rivers. Its two main tributaries, the Lot and Tarn, drain the Massif Central, whereas the Garonne and Adour drain the Pyrenees from a network of gaves (streams). The upper reach of the Garonne has a relatively steep gradient of 7 m/km, gradually decreasing to 0.7 m/km near the Tarn confluence. The mean annual flow of the Garonne ranges between 199 m³/s at Castelsarrasin to 615 m³/s at La Réole. The sediment yield of the Garonne is relatively high (10-70 tons/km²/yr), with a majority of sediments originating in the Pyrenees during high flow periods. The flow regime is highly variable with most floods occurring in spring and autumn. Floods are divided into three types: Pyrenean oceanic floods, classic oceanic floods, and Mediterranean floods. Pyrenean floods occur across the entire catchment, and peak in May-June. Classic oceanic floods occur from December to March and are predominant west-southwest of the Massif Central. Finally, Mediterranean floods are caused by downpours that occur typically in autumn and affect the western side of the Massif Central (Descy 2009).

The rivers flowing along the narrow coastal plain in northern Spain are short, draining into the Atlantic Ocean via the Bay of Biscay. These rivers transport large amounts of water due to high rainfall in the Cantabrian Mountains. Most streams and rivers, like the Agüera, are fast-flowing with a high gradient. The average annual discharge of the Agüera is 2-4.5 m³/s at its mouth (Sabater et al. 2009).

Terrestrial habitats

This ecoregion comprises a number of forested terrestrial ecoregions. The Cantabrian mixed forests in northern Spain comprise mixed deciduous broadleaf forests, including relict Mediterranean evergreen oak forests of Quercus ilex and Q. suber, as well as Tertiary relict species like Laurus nobilis, Arbutus unedo, and Rhamnus alaternus. The Atlantic mixed forests in southwest France include mixed oak forests dominated by Q. petraea and Q. pubescens, as well as planted forests of Pinus pinaster. There are also unique dune systems along the coast of Les Landes. The Mediterranean coast of France is dominated by mixed evergreen (Q. ilex, Q. suber), deciduous broadleaf (Q. pubescens), and conifer species. Other terrestrial ecoregions include the southernmost part of the Western European broadleaf forests and a section of Alps conifer and mixed forests (WWF 2001).

Description of endemic fishes

There are around a dozen endemic species and no endemic genera in this ecoregion. The apron (Zingel asper) was once widespread throughout the Rhône, but now occupies between 100 and 200 km in the basin (Keith et al. 2011). The Bearn beaked dace (Leuciscus bearnensis) is restricted to the Adour drainage, whereas the toxostome (Parachondrostoma toxostoma) is found throughout the Rhône, Var, Hérault, Adour, and Garonne drainages. The Ebro nase (Parachonrostoma miegii) is found in the eastern Cantabric slope. Several species of sculpin are also restricted to this ecoregion. The Lez sculpin (Cottus petiti) is located in a cold, karstic spring near Montpelier, France; the Hérault sculpin (C. rondeleti) is restricted to the Hérault drainage in southern France; the Adour sculpin (C. aturi) is restricted to the Adour and Nivelle drainages; and the Pyrenean sculpin (C. hispaniolensis) is restricted to the southern (Pyrenean) Garonne drainage. Other endemics include the Languedoc minnow (Phoxinus septimaniae) in the Languedoc and Roussillon rivers and beyond; Languedoc gudgeon (Gobio occitaniae) in the Garonne drainage; Mediterranean barbel (Barbus meridionalis); and Rhône trout (Salmo trutta, Mediterranean lineage), which is found in the Rhône drainage except Lake Geneva (Kottelat & Freyhof 2007; Keith et al. 2011). Near-endemics include the Pyrenean gudgeon (Gobio lozanoi) native from the Adour and Bidasoa drainages (Leunda et al. 2009); Pyrenean minnow (P. bigerri) in the Adour and Ebro drainage and rivers of Cantabric slope; and Pyrenean stone loach (Barbatula quirnardi), which is distributed in the Lez to Tech drainage and Adour and Garonne in France, and between Bidasoa and Nervión drainages in Cantabric slope of Spain.  The toxostome and Lez sculpin are Vulnerable, and the Hérault sculpin and apron are Critically Endangered according to the IUCN Red List (www. iucnredlist.org).

Other noteworthy fishes

Some of the most threatened fish in the ecoregion include the European Atlantic sturgeon (Acipenser sturio, CR), Hérault sculpin (Cottus rondeleti, CR), Lez sculpin (C. petiti, VU globally and CR in France), European eel (Anguilla anguilla, CR), toxostome (Parachondrostoma toxostoma, VU), bermejuela (Achondrostoma arcasii, VU), located in the Galician rivers (Leunda et al. 2009), and apron (Zingel asper, CR) (www.iucn.org; UICN et al. 2010).

The European Atlantic sturgeon was once abundant throughout Europe along the coasts and major rivers, including the Rhône. Since the late 19^th century, however, it has declined significantly. Today it is now restricted to the Gironde-Garonne-Dordogne drainage, predominantly in the Gironde estuary (Kottelat & Freyhof 2007; UICN 2010).

Another notable species is the Atlantic sea lamprey (Petromyzon marinus), which is a monotypic species that is parasitic on a variety of other fish and cetaceans, including whales (Kottelat & Freyhof 2007).

Ecological phenomena

There are a number of diadromous species, including the anadromous European river lamprey (Lampetra fluviatilis), Atlantic sea lamprey (Petromyzon marinus), allis shad (Alosa alosa), twaite shad (Alosa fallax fallax) and Rhône twaite shad (Alosa fallax rhodanensis); and the catadromous European eel (Anguilla anguilla) (Lassalle et al. 2009). Atlantic sturgeon (Acipenser sturio) was once common in the Rhône, but is now locally extinct. It does, however, still exist in the Garonne drainage (Lassalle et al. 2010).

Justification for delineation

Southern European ecoregions were delineated based on a bottom-up approach employing both published and unpublished field data and expert assessment (Abell et al. 2008). It is distinguished from the more uniform climate and fauna of the Central and Western Europe [404] to the north by endemics (for example, in the genera Leuciscus, Gobio, Cottus, Phoxinus) as well as greater seasonality with drier summers, partly seasonal flows, and flash floods (M. Kottelat pers. comm. January 6, 2006).

Level of taxonomic exploration

Good