Invasive species threaten US biodiversity

As 2010, the UN's International Year of Biodiversity, gets underway, a fight against some of the most damaging invasive species in US waterways is heating up. From IPS, part of the Guardian Environment Network
Matthew Berger, from IPS, part of the Guardian Environment Network
guardian.co.uk 5 Jan 10;

As 2010, the UN's International Year of Biodiversity, gets underway, a fight against some of the most damaging invasive species in US waterways is heating up.

The UN says some experts put the rate at which species are disappearing at 1,000 times the natural rate, and invasive species – which consume the food or habitat of native species, or the native species themselves – are one factor contributing to this acceleration. Climate change is another major factor.

"Often it will be the combination of climate change and [invasive] pests operating together that will wipe species out," says Tim Low of the Australia-based Invasive Species Council.

The International Union for Conservation of Nature says that 38% of the 44,838 species catalogued on its Red List are "threatened with extinction" – and at least 40% of all animal extinctions for which the cause is known are the result of invasive species.

But just as invasives are not the only threat to biodiversity, the threat to biodiversity is not the only problem caused by the havoc – ecological as well as economic – wreaked by species that are transported to a foreign habitat, get a foothold there and spread, often voraciously.

The UN Convention on Biological Diversity says the spread of invasives costs 1.4 trillion dollars a year globally in damages and control measures. The US alone loses 138 billion dollars a year in the fight.

The problem can be seen throughout US waterways, from Asian clams in California's Lake Tahoe to snakehead fish in the East Coast's Potomac River. One of the most immediate threats – Asian carp – is currently on the doorstep of the Great Lakes ecosystem, where it could decimate a seven-billion-dollar fishing industry among other economic and ecological assets.

After being imported to the south-eastern US in the 1970s for use in containing aquatic plants, bighead and silver carp, collectively referred to as Asian carp, eventually escaped from fish farms there and made their way north via the Mississippi River. They have taken over stretches of adjoining waterways such as the Illinois River and evidence was found in November that the fish are within seven miles of Lake Michigan.

The concerns over what a carp infestation might mean for the Great Lakes' industries and environment are several-fold. Asian carp are voracious eaters, consuming 40 times their body weight in a day, and females can carry a million eggs and spawn multiple times in a season.

Silver carp, which can top out at 1.2 metres and 45 kilogrammes, jump far out of the water at the sound of a boat motor. They are generally unappealing to U.S. consumers as food fish due to the floating bones in their flesh.

The battle over how to protect the Great Lakes ecosystem – which accounts for 20% of the world's freshwater – has now made it to the US Supreme Court, where Michigan and other Great Lakes states are suing the state of Illinois to temporarily shut canals in the Chicago area that connect the Mississippi River system to Lake Michigan, thus blocking the fish's path until a tenable solution is agreed.

The lakes have been hit before. Zebra mussels, for instance, have colonised the region's waters beginning in the late 1980s. Zebra and quagga mussels, both of which were most likely transported to the US in the ballast water of trans-oceanic ships, have since spread across the country, clogging pipelines and water intakes at significant economic cost.

At Nevada's massive Hoover Dam, quagga mussels have forced some turbines to be temporarily shut down, affecting 1.6 million electricity users.

In terms of damage to biodiversity, Asian carp crowd out other species by simply eating and reproducing more and faster. They make up 95% of the biomass in some stretches of the Illinois River. Similarly, when the Nile Perch was introduced to Africa's Lake Victoria, 100 to 150 endemic fish species were wiped out.
The role of climate change

Local species may become even more vulnerable to certain invaders as the effects of climate change are increasingly felt and habitats are disrupted by phenomena such as warmer temperatures and rising sea levels.

"We know invasive species can capitalise on these disturbances," says Scott Loarie, a co-author of a study in the current issue of the journal Nature which points out how fast species will have to migrate to keep pace with a changing climate. As ecosystems are transformed, "weedy-type species might be able to adapt and expand better than the original species," he says.

"In Australia, temperatures have risen the most at the highest altitudes, and these are the places where invasive species have multiplied the most," says Low. "In the Australian Alps, introduced foxes, rabbits, hares, house mice, horses and weeds have all increased either in numbers or in range."

The effects on biodiversity are evident. "The foxes are a real concern", he says, explaining that the Bogong moths that used to be a major food source for foxes are migrating to the mountains later in the season due to changing temperatures. This means foxes are preying on other species, such as the endangered mountain pygmy possum, which also rely on the moths for food and are now forced to spend more time in the open searching for food.

A changing climate is likely to hit aquatic species quickest. A recent study by researchers at Nasa's Jet Propulsion Laboratory found that lake surface temperatures in six Northern California and Nevada lakes are, on average, warming at twice the rate of the surrounding air.

One potential fallout of this trend is a more hospitable environment for invasive species, like the Asian clam that first appeared in California's Lake Tahoe at the beginning of this century but which is now prevalent enough that its waste has caused algae blooms in the lake's tourist-drawing crystal waters.

On the other side of the globe, river flows are decreasing in West Africa due to less precipitation at their sources, a result of climate change. This has allowed the South American native water hyacinth to prosper. The hyacinth clogs rivers and water intakes, blocks sunlight, and crowds out native species.

Back on the land, plants like serrated tussock have invaded grazing land in Australia and elsewhere, pushing out the native grasses livestock depend on with devastating speed. Low says invasive plants alone cost Australia over 3.5 billion dollars in agriculture losses and control efforts.

And the mountain pine beetle, aided by milder winter temperatures, is devastating British Columbia forests. Changing temperatures have also allowed the beetle to move to higher latitudes. It is expected to kill almost 80 percent of pine in the province by 2015.

The list goes on.

Though climate change is only one factor in the spread of invasives, these intruders are generally given a leg up by the disruptions caused by a changing climate since they are typically very hardy species and adept at capitalising on opportunities to colonise areas.

"Climate change is creating some difficult conditions for a number of living organisms and most of the invasive alien species are more resistant, more opportunistic than the organisms in a given place," the U.N. Convention on Biological Diversity's Kalemani Mulongoy said in November.