Over the weekend, a Chinese Mitten Crab (Eriocheir sinensis) was caught in salt water off Nyborg. While the crabs have been invaders in Denmark for almost 100 years, they have not had the same rate of expansion or damages as in German waters, so far. As a top 100 world invader, Danish fishermen and researchers have been on the lookout for the crab, but only recently is it turning up in salt water, where it goes for breeding purposes.

EU regulations are also driving this attention to the crab’s presence. The crab is one of the 10 species in Denmark that EU Invasive Species Policy aims to eradicate from EU waters. Detection and response are direct functions of awareness!

The reasons behind the current expansion are not well understood, but improved water quality may, perversely, be part of the story behind the crab’s increasing success. There could, however, also be additional introductions via ballast water, for example, or additional factors driven by changes in temperature or climate that we don’t fully understand. We can, however, expect that increasing changes in climate will increase the chances of other species invasions, just as we can expect that increasing maritime traffic and trade over the last century has already had impacts of which we may not be aware.

It is not particularly unusual for invasive species to have a long period between initial introduction and successful expansion – they may need to await another species introduction for prey or symbiosis, for example. Nor is it particularly rare that improvement in one dimension of environmental quality might threaten another. The case here highlights the importance of understanding integrated ecological and economic factors, beginning with, but extending far beyond, the basic biological characteristics of the species.


Photo Credit: Christian Fischer. The ”Chinese mitten crab”, ”Eriocheir sinensis”. This male specimen had been caught with many others by a fisherman in the Havel River in the state of Brandenburg, Germany. https://nl.wikipedia.org/wiki/Bestand:EriocheirSinensis5.jpg