Boundaries

This ecoregion represents the lower Tigris-Euphrates river system. It is bounded by the Zagros Mountains to the east, the Persian Gulf to the south, the deserts of Arabia and Syria to the west, and the Turkish Highlands to the north. Surrounding ecoregions include the Upper Tigris & Euphrates [442] to the north and east and Arabian Interior [440] to the west.

Topography

Most of the ecoregion is comprised of large marsh and lake areas that are surrounded by a flat landscape which drops 4 cm/km over the lower 300 km of the Euphrates and 8 cm/km along the Tigris. The Tigris and Euphrates meander across the plain and end up partly as an inland delta with extensive marshes near the head of the Persian Gulf. The mean elevation is around 200 m.

Freshwater habitats

The lowlands of Iraq, known as Mesopotamia (“land between the rivers”), have extensive marsh and lake habitats fed by the two main rivers. Tributaries of the Tigris originate in the Zagros Mountains. Spring floods feed the marshes and lakes from snow melt. The lakes in central Iraq were saline depressions that were converted to store water for flood control, and now support a fish fauna. The marshes dry out naturally in some years but have been devastated by drainage schemes.

Terrestrial habitats

This low-lying alluvial plain is surrounded by xeric shrubland and desert, which is often saline. Today, much of the water of the Tigris and Euphrates rivers has been diverted for irrigation, dams, large cities, and intensive agriculture. Vegetation of the marsh areas consists of Phragmites (reeds), Typha (rushes), and Cyperus (papyrus).

Description of endemic fishes

There are three endemics in the ecoregion: Glyptothorax steindachneri, Caecocypris basimi, and Iraq blind barb (Typhlogarra widdowsoni). Caecocypris basimi and the Iraq blind barb are endemic genera and species from a cave habitat near Haditha on the Euphrates, and are listed as Vulnerable in the Red List. A near-endemic cyprinid, Hemigrammocapoeta elegans, is probably restricted to the lowlands, as is an undescribed tooth-carp (Aphanius sp.). A sisorid catfish is only known from its original description but may be a synonym.

Other noteworthy fishes

The bull shark (Carcharhinus leucas) once entered the Tigris River as far up as Baghdad.

The fauna is dominated by various members of the genus Barbus, some of which exceed two meters in length. Others are keystone species in the marshes and rivers and have been significant food sources for humans for at least 6000 years.

Ecological phenomena

Hilsa shad (Tenualosa ilisha) is an important food fish that enters the southern parts of this basin to spawn. Various marine species also enter the southern rivers and marshes, but most are casual visitors. Many freshwater fishes move between the marsh and riverine habitats for spawning, feeding, and overwintering.

Justification for delineation

This ecoregion includes one of the world’s major wetlands with large rivers and formerly extensive marsh habitats. The Shadegan Marshes and associated mudflats in southern Iran is a Ramsar site.

Level of taxonomic exploration

Good