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Alien Invasion

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Algae Alert 2 pages: | 1 | 2 |

Photo of Alex MeineszIn "Green Invader," Alan Alda gets a scuba tour of the Mediterranean seafloor from biologist Alex Meinesz . The devastating impact of Caulerpa taxifolia is immediately apparent - miles and miles of green algae waving in the current, all other signs of life absent. Caulerpa grows at a fantastic rate, choking off native plant species and the animals that depend on them. Meinesz has been studying Caulerpa for over twelve years, and is the recognized authority on this alien invader. Here, he updates the situation in the Mediterranean and around the world. Especially significant in the Mediterranean is the latest affected area - Tunisia. This is the first infestation of the southern Mediterranean coast, threatening the rich fisheries vital to the economies of North African countries.
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Innocent Origins

Vegetative reproduction means that just a fragment of Caulerpa can give rise to an ocean's worth of algae.

Several lines of evidence suggest that the particular strain of Caulerpa taxifolia currently threatening the Mediterranean Sea was accidentally released in 1984 in front of the Oceanographic Museum of Monaco. This strain, cultivated in European aquariums since 1960, is characterized by its large size, vigorous growth, resistance to cold water, and particularly high toxicity.

Recent genetic testing has revealed that all the Caulerpa colonies spreading in the Mediterranean Sea are identical to strains used in European public aquariums. Since the invasive strain of Caulerpa does not reproduce sexually, all the invasive algae are clones of a single individual. This mode of reproduction- called vegetative- means that just a fragment of Caulerpa can give rise to an ocean's worth of algae.

World Traveler

In June of 2000, new settlements of invasive Caulerpa were found in San Diego and Los Angeles, California. The species was previously unknown along the central Pacific coasts of the Americas. Subsequent genetic studies have shown that the Californian strain is identical to the European invasive strain. New accidental introductions via the aquarium trade are the suspected origin of the Californian settlements.

In 2000 and 2001, populations of invasive Caulerpa were noticed near Sydney, Australia in a temperate region some 375 miles south of the natural range of the species. Also resistant to low water temperatures, Australian specimens are genetically very similar to the aquarium/Mediterranean/Californian strain, with some DNA sequences being exactly the same.

Photo of fish in aquarium
Caulerpa is used in tanks like this at the Monoco Oceanographic Museum and around the world.

Worldwide analysis of natural Caulerpa populations - including specimens from the Atlantic and Pacific Oceans, the Red Sea, and the Indian Ocean - revealed that the strain cultivated in aquariums and currently invasive in the Mediterranean and California originated in Moreton Bay near Brisbane in South East Australia. The colonies of the algae found in Sydney are also related to this Moreton Bay population and must be considered a local introduction.

All these data show that the invader is a particular robust strain selected by the aquarium trade, cloned first artificially for use in the aquarium, then naturally in the open sea. This invader could threaten all the world's temperate coastal ecosystems.

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