Invasive Crayfish on Land: Orconectes limosus (Rafinesque, 1817) (Decapoda: Cambaridae) Crossed a Terrestrial Barrier to Move from a Side Arm into the Danube River at Szeremle, Hungary

Non-indigenous crayfish species have successfully invaded many European lentic and lotic ecosystems in the past 120 years. Orconectes limosus (Rafmesque, 1817) has one of the largest distribution areas from among these taxa. Its invasion front has recently reached the Lower Danube while it has also been gradually colonising Middle Danubian tributaries and adjacent areas in the Carpathian Basin. A further characteristic with invasion implications was observed along the Danube River at Szeremle, Hungary. On 28th September, 2011, at 3.15 pm an adult individual of O. limosus was observed walking from the Szeremle dead arm towards the Danube River. The river and the Szeremle arm are separated by a dike during low and medium water levels. The individual crossed successfully the dike and covered a distance of approximately 20 metres between the two separate water bodies. It is the first record of O. limosus in the Danube River catchment crossing on land from one water body into another. This behaviour definitely helps the colonisation of new water bodies when only small stretches of land separate inhabited and non-inhabited water bodies. It may also help the exchange of individuals between neighbouring populations, as well as to allow the use of terrestrial escape routes in case of desiccation or pollution of the water body.