Boundaries

The ecoregion is located within Russia between the Sea of Asov and Greater Caucasus Mountains. It encompasses the entire Kuban River catchment, including the estuary and deltaic limans (lakes/lagoons/bays).

Topography

The Greater Caucasus Mountain Range dominates the eastern side of the ecoregion with elevations rising over 4800 m.

Freshwater habitats

Originating from glaciers in Elbrus in two outflows, Ullu-Kam and Uchkulan, the Kuban River flows 906 km from the Greater Caucasus Mountain Range north and then west to the Sea of Asov. Its drainage area (61,000 km²) includes both mountainous rapid streams and lowland sections.  The area extending from the river’s left bank is mountainous with a general decline to the north and northwest, whereas the lower right side is lowland plain. In its upper reaches it is a typical mountain river with large slopes and riffles flowing in deep crevices covered by forest. Below Nevinnomyssk, the Kuban River comes to the plain where its valley extends. Meandering, it flows through pebble river beds, forming islands and rifts. Below the influx of the Laba, Belaya, and Pshish rivers, water yield grows notably and reaches its maximum near Krasnodar. Today, this area is dammed and converted into the Krasnodar Reservoir.

A distinctive feature of the Kuban River drainage is the irregular pattern of the river network, determined mostly by terrain features and history of riverbed formation. Whereas the right side of the Kuban River is completely devoid of tributaries, the largest number of watercourses is concentrated in the left part of the basin where numerous tributaries of the Kuban River flow from the ridges of the Greater Caucasus. The largest of these – Laba, Belaya, Teberda, Bolshoi Zelenchuk, and Malyi Zelenchuk – originate from glaciers and are characterized by a high discharge. Melting of abundant seasonal snow and glaciers takes place in June through July. In the middle and lower current spring begins much earlier; and as early as March the water level in rivers begins to rise. Thus the period of spring tide in the lower reaches of the rivers lasts 5 to 6 months. Against the background of the total rising water level, floods from intensive precipitation also occur. In winter the Kuban River is supplied by permanent subsoil water flow. In the plains it freezes on average for 10—20 days.

In addition to the riverine habitats are the ecoregion’s estuary and deltaic limans (lakes/lagoons/bays). These limans are freshwater or brackish water coastal lakes, lagoons, and bays that are now more or less isolated from the river and/or the sea. However, historically, they were once all connected with the former or extant Kuban Delta. The Kuban River once had a highly diversified delta and drained to both the Black Sea and the Sea of Azov.

Terrestrial habitats

The ecoregion falls within three terrestrial ecoregions: Caucasus mixed forests in the south, Crimean Submediterranean forest complex in the central part of the ecoregion, and Pontic steppe in the north. The Caucasus mixed forests are located at the intersection of at least three biogeographic provinces, and also lie in an area of high landscape and habitat diversity. This has resulted in high species richness and endemism. The mid-elevation forests are dominated by species such as Georgian oak (Quercus iberica), hornbeam (Carpinus caucasica), sweet chestnut (Castanea sativa), and Oriental beech (Fagus orientalis). At higher elevations coniferous forests are dominated by species like fir (Abies nordmanniana) and spruce (Picea orientalis). The Crimean Submediterranean forest complex also has high plant endemism, and is composed of montane mixed coniferous forests dominated by fir and spruce.

Description of endemic fishes

The predominance of endemic species in the genera Gobio, Romanogobio, Squalius, and Chondrostoma reflect the ancient origin of the ecoregion’s primary freshwater fish fauna from the Tertiary Palearctic fauna of Siberian (Central Asian) origin. Geological isolation resulted in the divergence of these genera into endemics such as the Kuban barbel (Barbus kubanicus), Gobio kubanicus, Little Kuban gudgeon (Romanogobio parvus), Kuban long-barbelled gudgeon (R. pentatrichus), Kuban’s nase (Chondrostoma Kubanicum), Sabanejewia kubanica, and Aphips chub (Squalius aphipsi). Oxynoemacheilus merga is also endemic.

The Kuban barbel (Barbus kubanicus) is the only species of this genus within the Kuban drainage. Its closest relative is the Terek barbel (B. ciscaucasicus) from rivers of Eastern Ciscaucasia. It prefers mountain and piedmont streams, with a fast current and a sandy, gravel, or rocky bottom. It is abundant and widespread, and spawns on gravel bottoms. It is rare in the lower Kuban since the construction of the Krasnodar Dam.

The closest relative of the Little Kuban gudgeon (Romanogobio parvus) is the North Caucasian longbarbel gudgeon (R. ciscaucasicus), which resides in rivers of Eastern Ciscaucasia. It is restricted to large, high gradient river sections with fast, but not turbulent, currents, and gravel or sandy bottoms. The species is abundant in the middle Kuban, but has a very restricted range.

The Kuban gudgeon (Romanogobio pentatrichus) is peculiar by having five – unique for gudgeons –  anal branched rays. It occurs in the same range and habitats as the previous species.

Kuban’s nase (Chondrostoma kubanicum) is the only species of the genus in the Kuban River. It prefers piedmont and mountainous rivers with a strong current and gravel bottom. In winter, it moves downstream to lower sections or larger tributaries. It is very sensitive to water quality, especially turbidity. It possibly declined during the 20th century because of construction of the Krasnodar Dam. It is still rather numerous in the middle and upper sections of non-regulated Kuban tributaries.

Aphips chub (Squalius aphipsi) is a near-endemic that occurs in southern tributaries from the Adagum to Laba systems in piedmont streams. It may be restricted to very small pools during summer. It spawns in shallow riffle habitats, with a strong current, a stony or pebble substrate, a water depth of 10-20 cm, and at temperatures over 20°C. It does not migrate for long distances, but moves downstream in winter to deeper pools, and in summer to the uppermost sections of streams. It is abundant throughout its range.

Other noteworthy fishes

Before the dams and reservoirs were constructed, the Kuban River had been famous for its migratory stocks of sturgeons (Acipenser gueldenstaedtii, A. stellatus, Huso huso) and cyprinids (Alburnus mento, Vimba vimba). Since then, the sturgeons have been almost completely extirpated, and the cyprinids became much less numerous, although they formed riverine stocks in reservoirs, and entered tributaries for spawning.

Aphips chub (Squalius aphipsi) is a near-endemic that occurs in southern tributaries from the Adagum to Laba systems in piedmont streams. It may be restricted to very small pools during summer. It spawns in shallow riffle habitats, with a strong current, a stony or pebble substrate, a water depth of 10-20 cm, and at temperatures over 20°C. It does not migrate for long distances, but moves downstream in winter to deeper pools, and in summer to the uppermost sections of streams. It is abundant throughout its range.

Ecological phenomena

TheKuban River andthe majority of its tributaries pass through all of the zones within the vertical zonation, which is pronounced, in the Caucasus. This has corresponded with distinct and successive species assemblages: trout dominate in high mountainous sections; further downstream Kuban barbel (Barbus kubanicus), stone loach (Barbatula barbatula), and European chub (Squalius cephalus) form the nucleus of the community; and then in the piemont to lowland sections Gobio, Romanogobio, and Aphips chub (Squalius aphipsi) is dominant. The lower reaches are mostly inhabited by non-endemic cyprinids from Rutilus, Alburnus, Petroleuciscus, and Chondrostoma genera and percids.

Justification for delineation

For ecoregions of the former Soviet Union, a species/genera/family presence/absence matrix was compiled for a hierarchy of hydrographic units, and cluster analysis and ordination techniques (Primer v.6 statistics software) were employed to assess biotic similarities among hydrographic units and to identify major faunal breaks. The Kuban fish fauna is distinct from other ecoregions of the Caucasus. The native fauna is also clearly distinct from that of Don [427], which is geographically close, but has a completely different geological history.

Level of taxonomic exploration

Good