Invasive animal species repeatedly find their way into foreign areas and displace the native species there. This is also the case in the Arno River in Florence, as a long-term study has now revealed. There, all but one native fish species have been replaced by alien species within 215 years. The same applies to snails, mussels and crustaceans. According to the researchers, the main reason for this is humans.
Extreme invasion of species: whether invasive crayfish in the USA, alien squid jellyfish in the Baltic Sea or pacific oysters in the North Sea – more and more non-native animal species find their way into foreign habitats through international travel and trade, which gives them ideal conditions for strong reproduction Offer. The problem: They endanger the local biodiversity because they compete for food, shelter and breeding grounds. If they establish themselves permanently, they usually even completely eradicate the original species.
How is the situation in the Arno?
An international team of researchers led by Phillip Haubrock from the Senckenberg Research Institute and the Frankfurt Nature Museum has now investigated how far advanced the invasion of species is in the Italian River Arno. The Arno is considered to be an important and, with a length of almost 250 kilometers, the second longest river in central Italy. It meanders through northern Tuscany to Marina di Pisa, where it flows into the Tyrrhenian Sea.
For their study, the scientists documented the development of the biodiversity of fish and macroinvertebrates in the Arno over a period of 215 years. In addition to their own surveys, they evaluated numerous historical documents and collections and spoke to local historians and researchers. “We were particularly interested in how the composition of the species living in the river and the diversity of species has changed – and which factors have led to this,” explains Haubrock.
Significantly more invasive than native species
The result: In all of the animal groups observed, significantly more invasive species than native species live in the Arno. While 92 percent of the fish population was still indigenous around 1800, 200 years later its share shrank to only six percent. “It can be said that in the Arno there has been an almost complete exchange of native species by immigrant river dwellers – the only fish that can be found here is the tench Tinca tinca, a species originally found in Italy,” says Haubrock. The remaining fish fauna of the Amos today consists of immigrated, non-native species.
The researchers found something similar for mussels, snails, crabs and other aquatic animals. Only 30 percent of the organisms of these groups living there today can be described as indigenous. Interesting, however: The change of fauna in the Arno had different effects on the biodiversity of the animal groups examined. “If you look at the entire period, the species diversity within the fish is increasing due to the immigrated species, but in the case of the macroinvertebrates we see a general decrease in the number of species – here the invasive species were unable to compensate for the loss of the native organisms,” summarizes Haubrock.
Main cause human
But how did the fauna exchange in the Italian river come about? According to the study, the increase in alien fish species is mainly due to the population growth in the region around Florence between 1900 and 1950. During this period, both the demand for food sources and the desire for recreational activities increased. “We were able to show that numerous fishing associations were founded during this period and that the citizens of Florence intensified their fishing activities – for this purpose, non-native species were also brought into the river in a targeted manner,” explains Haubrock. In addition, the Arno was channeled and deepened. As a result, the current increased and the sediment was removed more strongly – environmental changes that the non-native animals, according to Haubrock and his colleagues, were better able to cope with.
“Human activity – the intentional and unintentional introduction of new species, changes in the course of the river and increasing environmental pollution – have led to the replacement of native species with invasive species,” says Haubrock’s colleague Peter Haase. The problem: “The Arno is not an isolated incident. In many German and European rivers, the proportion of non-native species has increased significantly over the past decades, ”the researcher continued. “We therefore need long-term studies with a uniform recording system in order to operate successful and sustainable environmental management here.”
Source: Senckenberg Research Institute and Nature Museums, Article: Global Change Biology, doi: 10.1111 / gcb.15442