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 In
"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
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Vegetative reproduction means that just a fragment
of Caulerpa can give rise to an ocean's worth of
algae.
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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.
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Caulerpa
is used in tanks like this at the Monoco Oceanographic
Museum and around the world.
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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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