First record of alien crustaceans Atyaephyra desmarestii ( Millet , 1831 ) and Jaera istri Veuille , 1979 from the Czech Republic

The alien crustaceans Atyaephyra desmarestii (Millet, 1831) and Jaera istri Veuille, 1979 were recorded for the first time in the territory of the Czech Republic. Atyaephyra desmarestii was found in May 2007 in the River Elbe near Liběchov and Jaera istri was found in August 2008 in the River Elbe at Děčín. Only a single specimen of Atyaephyra desmarestii was collected, while Jaera istri was found in tens of specimens and was the most numerous aquatic invertebrate on site.

The species that have colonized the Czech stretch of the Elbe have now been joined by two other alien species -Atyaephyra desmarestii (Millet, 1831) and Jaera istri Veuille, 1979.

Atyaephyra desmarestii
The freshwater shrimp Atyaephyra desmarestii was found for the first time in the territory of the Czech Republic in a hand-net sample on May 2nd, 2007.The sample was obtained by 3 min.of multihabitat kick-sampling in the River Elbe at Liběchov.This site (Figure 1) is located on the right bank of the River Elbe (50°24'08"N, 14°26'58"E) at an altitude of 155 m asl.Only one specimen was collected, and repeated visits did not yield any more shrimps.
The nearest recorded sighting in the River Elbe is close to Tangermünde (Germany) (Thomas Ols Eggers, pers.comm.), which is approximately 500 km downstream.The individual collected in Liběchov therefore most likely reached the Czech territory via human activities, possibly in ballast water.It is unlikely that the shrimp was released or escaped from aquarium culture, as it is not a commonly bred species; however, this possibility cannot be excluded.Time will show whether this was just a single specimen that did not reproduce, or whether a vital population of this species will settle in the Czech stretch of the Elbe.
The native range of Atyaephyra desmarestii is the Mediterranean.At the end of the 19th century, it spread to Western and lately to Central Europe (Tittizer et al. 2000).It is impossible to confuse this species with any other crustacean in Central European inland waters thanks to several morphological features, for example its serrated rostrum (Figure 2) or the presence of a tuft of setae on its chelae (Anastasiadou et al. 2006).We do not consider this species to be a threat to native fauna of the Czech Republic because it seems that in Western and Central Europe it lives at its ecological limits (Van Den Brink and Van Den Velde 1986) and it does not reach densities that could have a negative impact in this area (Grabowski et al. 2005;Wittenberg 2005).

Jaera istri
Jaera istri was found for the first time during a faunistic survey of the Elbe gravel bar at Děčín (Figure 1) on the right bank of the River Elbe (50°46'27"N, 14°12'27"E).Three individuals were found on August 20th, 2008.Two weeks later there were already tens of specimens at this site.Unlike Atyaephyra, the invasion of Jaera was not surprising because it was known to be present in the German part of the Elbe close to the border (Beilharz et al. 2005) and it was predicted to reach the Czech stretch within a short space of time (Petrusek 2006).Jaera most likely crossed the German-Czech border spontaneously without direct human influence.Confusion with other species known to live in the Czech Republic is unlikely.There are two other species of aquatic isopods living in the Czech stretch of the Elbe -Asellus aquaticus (Linnaeus, 1758) and Proasellus coxalis (Dollfus, 1892).They differ from Jaera (Figure 3) in their body form and size.Interactions between Jaera istri and other aquatic invertebrates are not well understood, but a potential negative effect on native fauna cannot be excluded, mainly due to its high densities (Bernauer and Jansen 2006).It was the most numerous invertebrate on the gravel bottom in Hřensko (Czech-German borders) in autumn 2008, with its population comprising 30% of the total number of aquatic invertebrates.