Paul Eccleston, The Telegraph 19 Feb 08;
Alien species are wreaking havoc on the world's oceans and river systems, say scientists.
Marine invasive species damage waters and land that native species and plants rely on to survive.And governments have to spend millions of pounds trying to get rid of them, says the Nature Conservancy study.
Examples in the UK include Floating pennywort (Hydrocotyle ranunculoides) a native of North America which was brought to Britain in the 1980s as a garden pond plant but which quickly spread to the wild.
The pennywort chokes rivers and streams depriving water creatures and plants of essential oxygen and light. Individual stems can grow up to 20cm in a day, creating a mat of vegetation up to 15m from the bank in one season.
Invasive and predatory marine animals which cause massive problems for our native creatures on waterways include the American mink, American crayfish, and the zebra mussel from the Caspian sea.
Once in the wild, these aquatic invaders cause massive disruption and with no natural predators and a benign climates they expand rapidly to nuisance proportions.
The latest study contains a global assessment of the impacts and causes of invasive marine species and says 84 per cent of the world's coasts are being affected by foreign aquatic species.
Stephanie Meeks, acting president and CEO of The Nature Conservancy, said: "Everyone in the world depends on healthy oceans and coasts for survival. Invasive species are severely impacting native plants and animals, and are causing significant economic damage at the same time.
"By understanding the scale and scope of these invaders, we are better equipped to stop them."
According to the study, in the journal Frontiers in Ecology and the Environment, international shipping and aqua culture are the major causes of the spread of harmful species introduction world-wide with 80 per cent of all invasive introductions accidental.
The economic costs of invasive species are huge with the US alone spending £60bn annually to control and repair damage from more than 800 invaders. Throughout the world's oceans, aquatic aliens damage economies by hitting fisheries, fouling ships' hulls, and clogging intake pipes. Some can also pose a threat to human health through disease.
Examples of the damage invasive species can cause include:
* The comb jellyfish carried to the Black Sea on a ship in the early 1990s. It devastated fish populations and disrupted the entire food chain by feeding voraciously on fish eggs and zoo plankton.
* The Pacific oyster was transported from Japan to be farmed in coastal waters around the world since the early 1900s. Once introduced, they aggressively attach themselves to rocks and group together, squeezing out other species. In Australia and elsewhere, this fast-growing species can smother prized native oysters and mussels, hurting local fisheries.
* Wild Atlantic salmon stocks in Scotland and Scandinavia are being decimated by new pathogens, while escaped farm salmon are weakening the genetic resilience of native fish. Each year, up to 500,000 salmon escape from fish farms in Norway alone.
* San Francisco Bay, California, is the most invaded aquatic region on earth. More than half of its fish and most of its bottom-dwelling organisms are not native and new species are being introduced at an alarming rate.
Jennifer Molnar, conservation scientist at The Nature Conservancy and lead author of the study, said: " "The scale of this problem is vast. Every day, thousands of vessels cross our oceans with invasive species hitchhiking on their hulls. Because of this, as many as 10,000 species are estimated to be in transit at any one time.
"Once alien species become established in marine habitats, it can be nearly impossible to remove them, The best way to address these invaders is to prevent their arrival or introduction in the first place."
