Two new invasive Ponto-Caspian amphipods reached the Pripyat River , Belarus

During a survey of the Pripyat River (part of the European central invasive corridor, within Republic of Belarus) in June 2008, we for the first time found two alien amphipod species of Ponto-Caspian origin: Obesogammarus obesus (Sars, 1896) and Obesogammarus crassus (Sars, 1894). The maximum number of specimens was found at sites close to river ports. The data on distribution of species along the Pripyat River show that during the last 10-15 years, the fauna of invasive Ponto-Caspian amphipods in the Belarusian part of the European central invasion corridor has become enriched with new species.

The Pripyat River, one of the largest rivers in the Republic of Belarus, is a crucial part of the so called European central invasion corridor (Dnieper > Pripyat > Bug > Vistula > Oder > Elbe> Rhine) (Bij de Vaate et al. 2002).Until now, however, the fauna of alien amphipods and other invaders in Belarusian part of the corridor has been poorly studied.In fact, there are only two communications concerning invasive amphipods in Belarus.Arbačiauskas et al. 2008).
In June 2008, we conducted a supplemental benthic survey along the Belarusian part of the Pripyat River (Figure 1, Annex 1).The samples were taken with a hand-net (mesh size 1 mm) from the depths of 0.3 to 0.5 m in biotopes with different bottom substrates (muddy bottom with aquatic vegetation, silty sand, etc.).The oxygen content and pH of the water there varied between 6.8 and 7.2 mg l -1 and from 7.4 to 7.7, respectively.The conductivity did not exceed 205 μS/cm.Aquatic vegetation was dominated by Ceratophyllum spp., Potamogeton spp.and, in some cases, by Elodea canadensis Michx.Macroinvertebrate samples were preserved in 4% formaldehyde for subsequent taxonomical identification in the laboratory conditions.The identification was executed according to Carausu (1943) and Mordukhaj-Boltovskoy (1969).The two new invasive amphipods, i.e., Obesogammarus obesus (Sars, 1896) and Obesogammarus crassus (Sars, 1894) were found during this survey.
Obesogammarus crassus (Figure 2) was common in samples from the middle and lower parts of the Pripyat River and had a high abundance especially in the Mykashevichy river port (Figure 1).In these sites O. crassus coinhabits with the other Ponto-Caspian amphipods: Dikerogammarus haemobaphes, Chaetogammarus ischnus and D. villosus, but the abundance of O. crassus is more higher and equal 80% from total abundance of other amphipods.
This species originates from the brackish lagoons of the Black Sea and is more euryhaline than O. obesus (Mordukhaj-Boltovskoy 1969).
O. crassus is known to have invaded the Baltic Sea shores, Curonian and Vistula lagoons but has not been recorded in the Vistula River itself (Grabowski et al. 2007).
Obesogammarus obesus (Figure 3) was found on two sites in the lower part of the river with low abundance.This species has entered the Prypiat River from the Kiev Reservoir (Ukraine), where it was acclimatized in 1965 (Alexandrov et al. 2007).O. obesus has extended its distribution upstream to the Volga River (Mordukhaj-Boltovskoy 1969) and has successively established itself in all sections of the Danube River and entered to the Rhine River via the Main-Danube Canal (Ketelaars 2004;Nehring 2006).
The results of the present study show that during recent years the fauna of invasive Ponto-Caspian amphipods in the Belarusian part of the European central invasion corridor has become enriched with new species.The new species reported in this paper were not previously found  in the Belarusian part of the Dnieper River and in the Vistula River.Only O. crassus was recorded in the Vistula Lagoon; this species is suspected to have invaded there from the Curonian Lagoon (Lithuania), where it was introduced in the 1960s (Jazdzewski et al. 2002).Currently six Ponto-Caspian amphipods inhabit the Pripyat River and three of them (D. haemobaphes, D. villosus, Ch.curvispinum) are distributed in all parts of this basin.

Figure 1 .
Figure 1.Location of records of Obesogammarus crassus and O. obesus in the Pripyat River (Belarus).