Exotic species

Every year a number of non-indigenous animals and plants arrive in the North Sea. They are known as 'exotic species'. These species are brought in from all over the world via aquaculture and shipping, on hulls or in the ballast water of ships.

This image provides a detail of living pacific oysters on a groin on a beach of Ostend. They have a flattened form and thus don't show the well known 'cupped' from. This is due to the adaptation to this particular environment with its harsh living conditions.

There are currently around 120 known exotic plants and animals in the North Sea as a whole. This figure is probably underestimated, as it is sometimes difficult to find out whether or not the species are indigenous. The major breakthrough came a few centuries ago, during the major voyages of discovery overseas. Our climate is unsuited to many newcomers and after a while they die out. However, the number of species that adapt and remain here permanently is increasing sharply.

Some of them have even developed so strongly that they now form a dominant part of our marine flora and fauna. This is the case, for instance, with the American jack-knife clam (Ensis directus). This species was found in our waters for the first time in 1987. Now the shells of this species are washed onto our beaches in their millions. Another recent example is the Japanese oyster (Crassostrea gigas). This species only became established here in the early 1990s, but now it can be found in huge numbers on groins and in our harbours.

Until recently only species were found that lived elsewhere in similar climates, but these days more (sub)tropical organisms become established in the North Sea. These species seem to feel perfectly at home here, because of the recent climate changes - the past ten years were the warmest of the last century. As a result, barnacles from New Zealand and the Mediterranean, shellfish from America and ascidians and algae from Japan now live along our coast

 What ecological risks do exotic plants and animals bring along?

 What measures can be taken to limit the risks?