A few examples of visitors who should have stayed at home. By Mark Little.
As world travel increased over the last five hundred years, so have incidents of biological clash, such as the appearance of a tropical seaweed, Caulerpa taxifolia, in Mediterranean waters, where it threatens local sea life (see story). Some famous examples of guests who outstayed their welcome are the African honey bees introduced to south America; the European snails that escaped from a gourmetís escargot farm and are now devouring the state of California; or the starling, 100 of which were released in New Yorkís Central Park in 1890 by a club of Shakespeare fans as part of a hare-brained scheme to introduce all the birds mentioned by the Bard.
The traffic has worked both ways. The blight which cause the Irish potato famine in the mid-19th century may have come from America. Another devastating example of an imported menace is the vine root louse, Phylloxera, which arrived in France with some vine cuttings from America and began to attack the local vines which, unlike the American stock, had no built-in resistance to the pest. First detected around 1868 in Bordeaux, within 25 years it had all but wiped out most of the vineyards in France, Spain, Portugal, Germany and Italy.
Gardeners in Spain are all too familiar with some of the other stowaways which have arrived in more recent times, in particular the citrus leaf miner and the South African geranium moth. The citrus leaf miner, which first made its appearance in Malaga in the early nineties, probably arrived here from Asia. Phyllocnistis citrella quickly spread, posing a threat to Spainís citrus industry.
The geranium moth, Cacyreus marshalli, is a native of South Africa, as are pelargoniums, or geraniums. It thrives in Spain because here, unlike in its homeland, it has no natural predators. It is believed to have arrived in Mallorca with a shipment of plants around 1987. Soon afterwards local gardeners started detecting unexplained damage to their geraniums, and it wasnít until 1989 that a German entomologist correctly identified the culprit. By 1992 it had reached mainland Spain, spreading to gardens on the Costa Blanca and Costa del Sol
Other threats have reached Spain under their own steam, including one recent arrival, the Ruddy Duck which is originally American but flew here from England, of all places. Now it poses a threat to the rare local White-headed Duck. The White-headed Duck was on the verge of extinction two decades ago, and only the constant vigilance of environmentalists helped bring the population back to a meager 400 or so breeding pairs which survive in the wetlands of Andalusia, representing some 20 per cent of the world population. But its cocky American cousin could reverse its timid come-back.
These American ducks are all the descended from three pairs which escaped from a British bird-fancierís menagerie in 1948. They became naturalized in the UK, where there are now several thousand, and many of them started heading south in search of fresh territory. They were first spotted in Spain in 1983, and ornithologists later were alarmed to discover that they were inter-breeding with the native species. Competition from their hybrid descendants may be too much for the White-headed Duck to cope with.
More often than not, damaging species are introduced purposely, either for commercial reasons or for sport. Fast breeding common partridges were introduced in central Spain by hunters, where they proceeded to inter-breed with the native Red-legged Partridge. Non-indigenous deer and chamois have caused havoc to the ecosystems of Spanish nature parks.
Spanish rivers have not been free from the meddling of over-enthusiastic sportsmen or even agricultural authorities. The native brown trout, for example, is being crowded out of its territory by the aggressive rainbow trout used to stock many rivers and streams. But perhaps the most spectacular example of an introduced fish species is the Siluro, the monster catfish which now lurk in the dams of the Ebro river.
A native of central Europe, the Siluro, or Wels, will gobble up just about anything as it hunts along the muddy bottoms of slow-moving rivers and lakes. It feeds on fish, frogs, water birds, and even small mammals which have the misfortune to fall into the water. It is Europeís largest freshwater fish, reaching a weight of more than 600 pounds and measuring up to 16 feet.
This voracious fish from hell appeared in the Mequinenza dam in Aragon, northern Spain, not long after it was built 25 years ago. Apparently, siluro fry were smuggled into Spain by a group of German anglers who were tired of fishing in the rain and fancied the idea of hooking their favorite catch in the Spanish sun. The small catfish proceeded to eat everything the damís water could offer, and every year they increase in size, some recent specimens reaching more than 300 pounds.
Spanish waterways are also threatened by invading Louisiana crayfish, which are a menace in two of Spainís most valuable wildlife areas, the DoŮana park and the Ebro delta, and a threat to Spanish rice farmers. Unlike the increasingly rare native crayfish, which only lives in the pristine, fast-running cold waters of mountain streams, these American cousins will live just about anywhere. Furthermore, the females can lay up to 500 eggs at one go.
This reproductive energy of the Procamabrus clarkii was precisely why they were introduced to southern Spanish fish-farms in 1974, as a cash crop. It was not a very successful experiment - Spaniards much prefer the local seafood - and they soon outgrew the bounds of the farms and became naturalized as an extremely damaging pest: they feed off the local animal species, they devour the young shoots in rice fields, they undermine river embankments with their tunnels.
But there was no stopping their spread, and within five years they had appeared in northern Spain. One more monument to the god of Really Bad Ideas.
Alien Attack: The Killer Seaweed
Copyright © Mark Little
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