The Danube River Basin is Europe’s second largest river basin. It spans the territories of 19 countries with a total area of 801,463 km², and can be divided into three sub-regions. This research focuses on the upper basin which extends from the source of the Danube in Germany to Bratislava in Slovakia.
Attempts to regulate the Danube, such as through the construction of dams, dikes, weirs and canals have precipitated in changes to the river profile such as its width, water depth and flow velocity. One negative effect is the modification of the aquatic environment which disconnects animals from their spawning grounds, disrupting the lifecycle of migratory species such as the sturgeons which cannot reach their spawning grounds and habitats in the middle and upper Danube River Basin. To highlight the extent of this negative externality, after the construction of impoundments at Jettenbach in 1921, professional fisheries operating near the River Inn (Germany) collapsed.
The effects of global warming, and the construction of Rip-raps which are large boulders artificially placed to fix riverbanks, provide optimal conditions for invasive species such as the round goby- a fish traditionally found in the lower stretches of the Danube and along the coasts of the Black Sea, but has since expanded into the upper basin. The goby threaten local fish species by rapidly adapting to their new habitat, and consuming a broad range of foods thus outperforming other species in resource acquisition.
By preying on flies, young fish and eggs, the goby reduces the diversity and abundance of invertebrates, gradually eliminating native fish species such as the barbel and European chub, which already account for over 70 percent of the entire fish population in some areas of their preferred habitat such as rip-rap banks. Native species are often easier prey as they have yet to developed defence mechanisms against the newcomers.
The round goby is just one of the five goby species advancing into the upper basin. The loss of biodiversity is serious and irreversible, once biodiversity is lost, the original ecosystem is unrecoverable. Nature always attempts to regulate and retain a balance in its ecosystem, the higher populations of burbot, a freshwater cod species that also lives in rip-rap prey on the goby, thus reducing the abundance of the goby invader. But with the myriad of detrimental effects caused by the regulation of the Danube, the ecosystem of the Danube remains highly volatile and uncertain.
By Andre Yeo