Invasive Fish Species in Danube River Creates Entirely New Ecosystem

Globalization is making a huge impact on ecosystems across the world. Invasive species are conquering native ones as aquatic environments in particular begin to shift. Now, scientists have discovered a fish species in the Danube River that's making a huge splash; not only is this invasive species conquering new habitat, but it's also creating a totally new ecosystem in the process.

Humans change their habitat like no other species. In order to improve passage for ships, we've straightened, deepened and reinforced river banks and have altered the natural force regime. This causes environmental changes to local systems that can impact the species that are already present.

There's one fish in the Danube River, though, that has caused quite a bit of havoc. The round goby has expanded its distribution range significantly to the headwater of the Danube as well as the Rhine, the Baltic Sea and the Laurentian Great Lakes in North America. In order to find out how much this fish has impact the ecosystem, though, the scientists took to the field.

"Round goby reached the headwater of the Danube only a few years ago," said Jorg Brandner, one of the researchers, in a news release. "Probably as a stowaway in the ballast water of ships. In fall 2010--just one year later--we found the first gobies in the river at Kelheim--around fifteen kilometers further upstream. We did not expect the invasion to progress so rapidly."

It turns out that round goby can consume a broad range of foods and thus can outperform other species when it comes to food competition. Over time, round goby eliminate native fish species, such as the barbell and the European chub. In fact, these fish are so successful that they already account for over 70 percent of the entire fish population in some areas.

That's not all round goby are doing. They're also reducing the diversity and abundance of invertebrates. Stoneflies, caddisflies and mayflies are being particularly hard hit as they become preferred prey. With the ability to quickly adapt to its new surroundings, the round goby is drastically impacting ecosystems.

In fact, the researchers found that the goby invasion has led to a "novel ecosystem" in the headwater of the Danube. This ecosystem is comprised of previously unknown combinations of species. Similar occurrences are also happening in other areas that the round goby is colonizing, including the Great Lakes of North America.

"What we are observing is a very flexible and robust network of different species that adapts itself perfectly to new environments," said Jurgen Geist, one of the researchers, in a news release. "Biodiversity is declining and once the original ecosystem is lost, we can never go back."

The findings are published in the journal PLOS One.