Exotics in fresh water

The number of exotic species of freshwater habitats has been increasing in the Netherlands, particularly in the last 50 years.

Trends

Exotic species of freshwater habitats have been increasing in the Netherlands since 1800. In the last 50 years in particular, many exotics have established and become common at regional or even at national scale. In addition there are many species that occur in only one or two localities.

Most (65%) of the freshwater exotics were not introduced deliberately in the Netherlands but are escapees from aquariums, garden ponds, and suchlike. Some 25% have arrived via canals that link rivers, and 10% have arrived via ships.

Technical note

In total there are 85 new arrivals: 20 fish, 5 amphibians and reptiles, 13 molluscs, 19 crustaceans, 8 other invertebrates, 19 higher plants and one moss species.

The data on exotics are from five sources pooled by Van der Velde et al. (2002). It is very likely that the number of species occurring in only one or a few localities prior to 1950 has been underestimated. Some of the species that occur in only one or a few localities have not settled in, i.e. their populations are not viable.

References

• Van der Velde, G., I. van Nagelkerke, S. Rajagopal en A. bij de Vaate (2002). Invasions by alien species in inland freshwater bodies in Western Europe: the Rhine delta. In: E. Leppakoski, S. Olenin en S. Gollash (red.). Invasive aquatic species of Europe. Distributions, impacts and management. Monographiae Biologicae. Kluwer Scientifc Publisher.