Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
NOVA Home Find out what's coming up on air Listing of previous NOVA Web sites NOVA's history Subscribe to the NOVA bulletin Lesson plans and more for teachers NOVA RSS feeds Tell us what you think Program transcripts Buy NOVA videos or DVDs Watch NOVA programs online Answers to frequently asked questions
Deep Sea Invasion

TV Program Description
Original PBS Broadcast Date: April 1, 2003

 

Deep Sea Invasion homepage

In 1989 marine biologist Alexandre Meinesz went diving off southern France and was stunned by what he saw: a dense blanket of waving green fronds stretching around him in every direction on the seabed. At first Meinesz had no idea what it was. Then he made the alarming discovery that a tropical alga had taken root in the cold water of the Mediterranean, wiping out native sea life wherever it grew. "Deep Sea Invasion" follows Meinesz on his scientific detective hunt to discover the source of this deadly organism, his uphill battle to alert authorities to its danger, and the struggle to find a non-toxic way to control it.

The invasive seaweed has since spread to harbors and coral reefs throughout the Mediterranean and even to Australia and southern California. Given its robust constitution and apparent lack of predators—so far only chlorine has slowed its growth—scientists are worried that it could devastate marine ecosystems around the world.

Meinesz, a professor of biology at France's University of Nice-Sophia Antipolis on the Mediterranean coast, identified the alga as a strain of Caulerpa taxifolia, a green alga native to the tropics. But this strain seems otherworldly compared with its tropical cousins. Not only does it thrive at a water temperature that should kill it, but it also produces a powerful toxin that makes it deadly to fish and invertebrates (though not to humans).

Caulerpa is almost impossible to eradicate, although an infestation in a lagoon in southern California seems to have been dealt a deathblow with a massive dose of chlorine, which killed not only the Caulerpa but everything else as well. In the search for a less drastic defense, Meinesz and other scientists have identified a tropical slug that is unique in producing an enzyme that allows it to eat Caulerpa and neutralize the toxin. Mindful that the slug may be yet another Frankenstein's monster, just like Caulerpa, scientists are pondering whether or not to set it loose.

Wherever Caulerpa grows it carpets the seabed in brilliant green foliage, like a golf course. And it flourishes virtually everywhere, spreading not by sexual reproduction but by a form of cloning known as vegetative reproduction. A single cell of the plant—snared on an anchor or in a fishing net—is all that's needed to introduce it to a new habitat.

Meinesz traced the secret of Caulerpa's success to the Wilhelmina Zoo in Stuttgart, Germany. In 1980, the zoo's aquarium staff chanced on this strain while searching for seaweed that could survive in the artificial conditions of aquariums. The strain was either a rare mutant that just happened to be collected in the wild or else a monster engendered at the aquarium itself—born of the harsh chemicals and bright lights bathing the fish tanks.

Hardy and decorative, Caulerpa seemed a blessing at first, and it soon became the most popular aquarium plant on Earth. The Monaco Oceanographic Museum obtained a sample, and it was in the harbor just beneath this institution—where famed oceanographer Jacques Cousteau was the director at the time—that Caulerpa was first spotted getting a toehold in nature. The killer algae have been spreading ever since.

Back to top

Hand-pulling is unfortunately no longer an option with the "killer algae," which now blanket over 30,000 acres of Mediterranean seabed.




Deep Sea Invasion Web Site Content
Chronology of an Invasion

Chronology of an Invasion
Follow the alarming spread of Caulerpa taxifolia around the world.

The Impact of Invasive Species

The Impact of Invasive Species
Alexandre Meinesz on the degrees of menace posed by alien invaders.

Battling Introduced Wildlife

Battling Introduced Wildlife
Daniel Simberloff on strategies for combating weed-like species.

Matching Aliens With Impacts

Matching Aliens With Impacts
Match 10 successful invaders to the damage they've caused.



Program Transcript

Program Credits



Send feedback Image credits
   
NOVA Home Find out what's coming up on air Listing of previous NOVA Web sites NOVA's history Subscribe to the NOVA bulletin Lesson plans and more for teachers NOVA RSS feeds Tell us what you think Program transcripts Buy NOVA videos or DVDs Watch NOVA programs online Answers to frequently asked questions

Support provided by

For new content
visit the redesigned
NOVA site