E. Leppäkoski et al. (eds.), Invasive Aquatic Species of Europe, 399-411 © 2002 Kluwer Academic Publishers. Printed in the Netherlands THE CASPIAN-VOLGA-BALTIC INVASION CORRIDOR YURY V. SLYNKO1*, LIUDMILA G. KORNEVA1, IRINA K. RIVIER1, VLADIMIR G. PAPCHENKOV1, GRIGORY H. SCHERBINA1, MARINA I. ORLOVA2 & THOMAS W. THERRIAULT3 1Institute of Biology of Inland Waters, Russian Academy of Science, Borok, Russia 2Zoological Institute, Russian Academy of Science, St. Petersburg, Russia 3Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Canada *Corresponding author [email protected] ABSTRACT The north-south transfer of species in the Volga River basin is not new, but the scale and nature of inva- sions changed along the Volga-Baltic corridor following transformation of the Volga River from a rive- rine environment to one of a series of cascading reservoirs. Southward penetration of northern species was facilitated by the formation of a cold-water hypolimnion in the Volga reservoirs. Following reservoir impoundment, 106 invasive species have been found in the Volga River basin, a process that occurred over two different time periods. The first period of invasions occurred between 1940 and 1970, and involved many northern species (77% of total species) moving downstream by passive dispersal. The second period of invasions is still on going and involves invasions by many Ponto-Caspian species (51% of total species) while new invasions by northern species has decreased substantially (7% of total spe- cies). The proportion of exotic species (i.e., invaders originating from basins not adjacent to the Volga basin) increased from 7% during the first period to 41% during the second period. Since the late 1970s, water temperatures in the Volga basin have continued to increase and it is postulated that many invasions during the second period are related to global climatic change. 1 Introduction: the formation of the European part of the Russian intercontinental waterway We define an aquatic invasion corridor as a system of waterways connecting previously geographically isolated river and sea basins, thereby allowing the active or passive dispersal of aquatic species beyond their historical, natural ranges. Also, available human-mediated vectors play a catalytic role in species dispersal along these invasion corridors. The Ponto-Volga-Baltic invasion corridor was formed along Europe's largest meridional river, the Volga River. The hydrology of the Volga has remained unchanged since the end of the Valday glaciation period (approximately 10,000 BP) and the entire catchment area is part of the Caspian basin (Obidientova 1977). The Volga River basin is divided into three main parts, the Upper, Middle and Lower Volga. The Volga-Ahtuba flood plain and the delta are considered separate parts of the Lower Volga (The Volga and its Life 1978). Berg (1962) attributed the entire basin to the Ponto-Caspian-Aral province of the Mediterranean sub-region while the basin itself belongs to the Palaeo-Arctic region. However, according to Starobogatov (1970) the entire Volga basin belongs to the European-Siberian sub-region and the Lower and Middle Volga are included in the Volga-Ural province, while the Upper Volga is included in the Baltic province. Indigenous biota of the Volga was formed by the end of Valday glacial period. Until recently, the Volga fauna consisted primarily of freshwater Palaeo-Arctic species with a unknown number of Ponto-Caspian species found in the Lower Volga. Even before the building of dams, the Volga River was an important transportation route in Russia. This fact greatly contributed to the uniting of territories from the Baltic to Black and Caspian Seas and the creation of a united Russia. Since the time of Peter the Great, attempts have been made to build a waterway connecting the Volga River and the Baltic, White, Caspian, Azov and Black Seas. Between 1703 and 1709 the Vyshnevolotsk Waterway was built to connect one Volga River tributary, the Tvertsa River, with the Msta River. Connections were also established with Ilmen and Ladoga Lakes and the Baltic Sea. In 1718 Vyshnevolotsk Reservoir was impounded, however this waterway never developed into a significant European transportation route. In 1810 the Mariinskaya Waterway was built, connect- ing the Volga River and the Baltic Sea through the Neva, Sheksna, Kovzha and Vytegra Rivers and through Ladoga and Onega Lakes. In 1811 another waterway, the Tikhvinskaya, was created to connect the Volga River with the Baltic Sea via Rivers Neva, Mologa and Ladoga Lake. In 1829 the Severo- Dvinskiy Canal was opened connecting the Volga River with the White Sea basin via the Sheksna, Suk- hona, Northern Dvina Rivers and Lake Kubenskoye. However, due to considerable seasonal and yearly water level fluctuations, regular ship traffic was not possible in this system until the 1940s. Full regulation of the Volga River flow was not possible until reconstruction resulted in the formation of the United Deep Waterway System of canals that was completed by the former USSR in the 1930s. New inter- and intra-basin canals and a cascade of reservoirs were constructed to maintain a constant depth of 3.5 m, a depth necessary for ship traffic. As a result, the speed of traffic, and consequently the amount of transported cargo, increased. In addition, the White-Baltic and Moscow Canals were built in 1933 and 1937 respectively. The latter formed a circular intra-basin waterway in Central Russia by con- necting the upper reaches of the Volga and Oka Rivers. In 1952 the Volga-Don Canal was opened pro- viding a direct connection between the Volga-Caspian Sea basin and the Azov and Baltic Seas. In 1964 the Volga-Baltic Waterway was fully reconstructed. A series of reservoirs along the Volga River were impounded including Uglich (1940), Rybinsk (1947), Verkhnevolzhskoye (1947), Gorki (1957), Kuybyshev (the largest; 1957), Volgograd (1960), Saratov (1968) and Cheboksary (1981) Reser- voirs. Impoundment of these reservoirs resulted in full regulation of the entire river channel except for the Volga-Ahtuba flood plain (The Volga and its Life 1978). In addition, Tsimlyansk (on the River Don), Sheksna, and Vytegra Reservoirs, the system of Kama River Reservoirs and several smaller man-made lakes were impounded to maintain the Moscow Canal. As a result of this development, the Volga River became the largest transcontinental waterway in Rus- sia. The river is 3,530 km long and its catchment area is in total 1,360 km2. There are 12 large and more than 300 medium and small reservoirs resulting in a total surface area of 25,660 km2 and a total volume of 180.5 km3, of which 85 km3 is considered usable (Avakyan & Shirokov 1994). The Caspian-Volga- Baltic route is responsible for more than 70% of all cargo transported by the Russian river fleet. With respect to cargo transportation, Volga River ship traffic is second only to the St. Lawrence Seaway (> 300 million tons per year by the mid 1990s; The Problem of Territorial Re-distribution... 1985). About 40% of the fleet transporting goods along the Volga River from the Ponto-Caspian region to the Baltic and White Seas belongs to the "sea-river" class. In 2000 an agreement was signed between Russia, India, Iran and Oman creating a united transportation corridor, termed the "North-South" corridor, in order to provide a transportation route between the Persian Gulf and Indian Ocean to the Baltic Sea (Enactment of the Government of Russian Federation 2000). A primary focus of this global venture is the Volga- Baltic Waterway, a waterway that is expected to handle 50 times more cargo than at present. In 2001 this transportation corridor entered the first stage of active development. 2 Early stage of biological invasions Since the creation of the canal and the intensified ship traffic during the 18th and 19 th centuries, increased invasions by several Caspian species have been noted. This is particularly true for species that prefer solid substrates and either foul ship hulls or are able to actively migrate in the littoral zone. For example, in the late 19th century the bivalve mollusc Dreissena polymorpha and the crayfish Astacus leptodactylus were found in the Northern Dvina River (Starobogatov & Andreeva 1994) and in the Baltic Sea (Nowak 1951). During the early 20th century, a mysid, Paramysis ullskyi and three amphipod species (Pontogammarus sarsi, Dikerogammarus haemobaphes and Corophiurn curvispinum) were found near the mouth of the Mologa River, a tributary of the Volga River (The Volga and its Life 1978). However, regulation of river flow between the 1940s and 1960s resulted in an even more pronounced invasion pattern. 3 Recent "North-South" invasions The early invasion sequence consisted of plant and animal species of northwestern limnophilic origins primarily due to the impoundment of the Rybinsk Reservoir, which started in the 1940s. The Volga- Baltic and Severo-Dvinsky Waterways provided major corridors for these invasions (The Volga and its Life 1978). The predominant donor waterbodies were large lakes in the Pskov, Leningrad, Vologda and Archangelsk regions (including Lakes Ladoga and Onega), and estuaries of large rivers in the Baltic and White Sea basins. Successful southward invasions by northern limnophilic species is determined primarily by environmental conditions including deceleration of river flow, formation of large lacustrine water bodies along the river channel (i.e. Rybinsk, Ivankovo and Kuybyshev Reservoirs), pronounced thermal stratification of water masses and existence of a cold water hypolimnion. Therefore passively moving pelagic limnophilic species of northern origin (algae, zooplankton and pelagic fish) have domi- nated among invaders between the 1940s and 1960s. 3.1 PHYTOPLANKTON AND AQUATIC VASCULAR PLANTS Between the late 1950s and early 1960s phytoplankton species of the genus Stephanodiscus (S. binde- ranus, S. hantzschii and S. minutulus) increased in abundance from north to south and now dominate the spring-summer algal community of the Volga River (Korneva 1999).