Invasive algae, plant, bivalve and crustacean species along the Hungarian Danube section: arrival time, colonisation characteristics, relative importance

Summary The status of invasive and potentially invasive species of the Hungarian Danube stretch was evaluated in four groups, algae, macrophytes, bivalves and crustaceans. With algae, potential invasive species are present in the aquatic system of the River Danube but no mass invasion occurred so far. Several invasive macrophytes were also detected, in some areas they have already become predominant. Invasive species are getting more important with bivalves, where they represent 15% of the local fauna and can reach high densities in several areas. Similarly, to that group, some alien crustacea species are also present in Hungary since the XIXth century, but their colonisation accelerated at the end of the 1990s and 2000s. They can become predominant or might even be the only representatives of their group along the Hungarian Danube section. The invasion of the above described species and several others basically alters the structure, dynamics and functioning of Danubian ecosystems. Due to the international importance of this process intensive co-operation is necessary to describe and mitigate the negative impacts of alien species along the Danube.