Alien Threats to Our Waterways
The arrival of the Quagga Mussel (Dreissena rostriformis) in UK waters has caught the mainstream media’s attention with an almost cataclysmic doomsday spark. Billed as the biggest single threat to British wildlife earlier this year and with its sheer potential for destruction of our ecosystems, the media can perhaps be forgiven for their foreboding atmosphere regarding it. Although our waterways are a focal point within this country’s culture, the threat to them from invasive species rarely makes headlines.
Ever since man started to move around the planet, so have other species as a by-product, either deliberately as a result of agricultural needs like the European Honey Bee to Australia or by accident carried on the hull of a ship. As man has colonised larger proportions of the planet, so to more species have moved around. Indeed the modern era has seen the exotic pet trade create established invasive species such as the Red Eared Slider (Trachemys scripta elegans) which saw illegal releases of unwanted pets exploit unused ecological niches in that environment and become established.
Although illegal releases can pose a threat, it is rare that they become established populations. However once populations do establish they can cause numerous detrimental effects notably by displacing native species and changing the food web of the environment. It is not only native species which should be concerned about the introduction of alien species, as they can also have severe economic impacts for us. Whilst Quagga Mussels pose a severe threat in that they meet all this criteria, they are not the only invasive alien species to grace our waterways with a detrimental impact.
Many aquatic species have been introduced into our waterways in the past for aquaculture. The signal crayfish (Pacifastacus leniusculus) is almost iconic of this. Introduced in the 1970’s for food purposes, it has since spread quickly across the UK aided by its ability to cross bodies of land to colonise adjacent waterways. Not only have our native crayfish been a direct casualty from this introduction as their populations have been all but obliterated, but they also undermine river banks by burrowing under them and prey upon native fish eggs.
The Brook trout (Salvelinus fontinalis) was intentionally introduced for the purpose of sports fishing, however it soon began to out compete and replace the native Brown trout (Salmo trutta). Not only can it alter the nutrient cycles of the water but it also poses a threat to the freshwater pearl mussel (Margaritifera margaritifera). Although this alien species has significant economic benefits for communities, these benefits will soon be lost if it replace native salmonids.
It is not only alien aquatic species which can pose a threat to our waterways; the Canadian Goose (Branta canadensis) has colonised the UK after being released for hunting and escaping from aviaries. Noted as a pest species they have various detrimental affects upon their new environment, ranging from habitat modification to the potential for air strikes upon aircraft. There is also the potential for them to cause algal blooms, as a result of eutrophication caused by nutrients from roosting geese. Of main concern however, is their ability to hybridize with native species, and their aggression towards smaller waterfowl which in turn displaces them.
Once a species does become established it is near impossible to remove and as the examples above show, alien species can have a variety of negative effects upon their new environments. The best combat against this is prevention, with all water users employing the “clean, check, dry” motto when they pack up their equipment to prevent any potential spread of invasive species. Water users are also encouraged to report any potential sightings of an invasive species: http://www.nonnativespecies.org/index.cfm?sectionid=81
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