Faxonius limosus (Rafinesque, 1817) (Decapoda: Cambaridae), a New Invasive Alien Species of European Union Concern in Bulgaria

A representative of the family Cambaridae (Decapoda) was recorded for the first time in Bulgaria. This is the North American spiny-cheek crayfish Faxonius limosus, considered as an invasive alien species of European Union concern. A total of 92 specimens (42 males and 50 females) were found in the Danube tributaries, the rivers Topolovets, Voinishka and Archar in northwestern Bulgaria, in 2015-2016. The morphometric characters of all specimens were studied and no significant differences were found between the three populations and between the males and females. Furthermore, the morphometric features distinguishing F limosus from the native crayfish species of the genera Astacus, Pontastacus and Austropotamobius in Bulgaria were presented. We assume that F limosus was introduced in Bulgaria through the Danube River, coming downstream from the Serbian and Romanian sectors, where this species have been recorded earlier. Our results also indicate an early stage of establishment of the species in the Bulgarian sector of the Danube River. The further spread of F. limosus upstream of the Danube tributaries and in the inland waters will threaten the native crayfish populations in Bulgaria. Therefore, urgent measures in accordance with the Regulation (EU) No 1143/2014 need to be taken at national and regional level in order to prevent the range extension and the negative impact of this invasive alien species in Bulgaria.