Recently, as the water temperature in Sweden’s seas has risen, more and more alien species have found their way here.
Some of these are the Asian crab species blue crab and small-spotted brush crab, which in the last decade have been found along the west coast.
– And it seems that they are doing just fine here, because they reproduce with a high level of well-being, says Matz Berggren, senior researcher at the Department of Marine Sciences at the University of Gothenburg, and adds:
– Unfortunately.
Could affect the perch tribe
According to Matz Berggren, we don’t really know how these crabs got all the way to Sweden, but their relatives were found in Europe already in the 90s and have since moved north.
The fact that it is alien species for Swedish waters does not necessarily need to be a problem, but alien species can become invasive if they disturb the ecosystem and have no natural enemy to balance them. And so it is with the blue crab and the brush crab.
On the one hand, they reproduce at a significantly higher rate than the beach crab that occurs naturally in Sweden, on the other hand, they eat pretty much anything, and on the other hand, they risk bringing diseases with them. And if the beach crab, and possibly other animals as well, are thereby pushed out by their immigrant rivals, the Swedish beach environment risks changing dramatically.
– They deal where they can, says Matz Berggren.
And even if they do not enjoy breeding as well in the Baltic Sea as on the West Coast, an establishment of the Asian crab species in Sweden could in the future lead to a reduced perch population.
– There is nothing in the Baltic Sea that is like crabs that eat everything, so you can raise a warning finger for the perch that lays its rum on the bottom.
“A swift blow with a stone”
But what can be done to prevent the spread of invasive crabs in Sweden?
– If you catch such a crab, it is very good if you report it to the Artportalen. We researchers can’t run around fishing for crabs everywhere, but all children who do that are doing extremely important citizen research. It’s the only way to get control, says Matz Berggren.
– Then you have to kill them with a quick blow with a stone.