Deep Sea Invasion

PBS Airdate: April 1, 2003
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NARRATOR: In the warm waters of San Diego, a team of marine biologists sets out on a routine dive. They're surveying the native eelgrass in this coastal lagoon.

In the beginning, everything seemed normal in this ocean paradise, where surfers ride the waves, and the lagoons are perfect for water sports. But below the surface trouble was brewing. The dive team moved slowly along the bottom. It was hard to see in the murky water. Then suddenly, they came face to face with an alien monster.

RACHEL WOODFIELD: You could just tell as you came up to it, there was trouble. It has a real insidious sort of creepy nature, as if it's some sort of blob that's taking over at the bottom.

GREIG PETERS (California Regional Water Quality Control): It's like out of a horror movie, but it's real.

NARRATOR: This is the alien, a seaweed called Caulerpa taxifolia. All seaweeds are algae, but this one is extraordinary. Caulerpa taxifolia is perhaps the largest single-celled organism in the world. One plant can grow nine feet long, and it spreads uncontrollably, turning lush marine landscapes like this into acres of green weed, an Astroturf®-like carpet and nothing more.

It was a scientific horror story. California had been invaded by a super algae that could overtake the Pacific Coast, and no one knew how to stop it.

But one man, 6,000 miles away, was all too familiar with this green monster. French seaweed expert, Alexandre Meinesz, had confronted Caulerpa taxifolia before. He found a patch of it a dozen years ago in the Mediterranean Sea and immediately sounded an alarm, but nobody listened.

ALEXANDRE MEINESZ (University of Nice, Sophia Antipolis): The authorities didn't want to know about the problem. We lost precious time when the algae could have been contained or maybe even eradicated.

NARRATOR: Today, about 40,000 acres of Mediterranean coastline is clogged with Caulerpa, and many scientists believe this beautiful sea is lost. Is America next? What can be done to stop this Deep Sea Invasion? Up next on NOVA.

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NARRATOR: This is Caulerpa taxifolia, a seaweed. And it's the most threatening underwater plant on earth. It can grow anywhere, at the astounding rate of one inch a day, pushing out everything in its path. Getting rid of it, if that's even possible, would require an all-out war, a biological battle between a weed and the scientists who understand the danger.

When Caulerpa taxifolia was discovered in San Diego, no one here had ever seen it before.

RACHEL WOODFIELD: We all knew when we saw it that it definitely wasn't something native. When I finally found a photo and the picture downloaded onto my computer, there was just a sinking feeling in my stomach.

NARRATOR: Within days, the infested lagoon was cordoned off like a crime scene, banned from human use and guarded by the police. Everyone now realized what could happen if they didn't act fast.

ROBERT HOFFMAN (National Marine Fisheries Service): We're assuming the worst case scenario: that if we don't control it, it's going to completely overtake this lagoon. And if we're wrong, I'd rather be wrong, over estimating the impact than underestimating it.

NARRATOR: The impact of alien species has been underestimated before. Africanized bees have killed more than a thousand people from Brazil to the United States, and now they threaten the American honey industry. With no natural predators, European gypsy moths have destroyed oak forests from Maine to the mid-west.

Today, thousands of alien plant, animal and insect species have invaded this country, costing hundreds of millions of dollars to control. But this seaweed may pose the worst threat of all.

Caulerpa taxifolia has already reshaped the Mediterranean Sea, mainly because no one listened to the one man who recognized the threat back in 1989. It all began here off the coast of Monaco.

One day, French marine biologist Alexandre Meinesz went diving in the Mediterranean. Meinesz is an expert on the marine life of the Mediterranean. He knew that among the dozens of plants that live here, one is fundamental to the sea's ecosystem. It normally covers large areas of the seabed. It's a dark, gray-green sea grass called "possidonia." Possidonia is a plant that provides food and shelter for a huge variety of fish and other sea creatures.

But that day, as Alexandre Meinesz dived, nothing was as he expected it to be.

ALEXANDRE MEINESZ: The water was very clear, the sun was shining, and visibility was good, and I saw straight away that the seabed was bright green. I said to myself, "This isn't possible. There shouldn't be any brilliant green seaweed here."

NARRATOR: Where Meinesz had expected to find the usual variety of Mediterranean sea life, all he could see for hundreds of yards was a dense, bright green mat of weed he'd never seen before. Everything was smothered in it.

ALEXANDRE MEINESZ: I went deeper, to the bottom. It was still there. Then I went to the west and to the east, and it was still there as well. I was really astonished at the size and extent of the algae. It struck me as being supernatural.

NARRATOR: As he studied the extraordinary new plant, he realized it was a giant variant of a tropical seaweed, or algae, called Caulerpa taxifolia. Yet how could a tropical plant survive in the colder waters of the Mediterranean?

ALEXANDRE MEINESZ: I didn't understand how such a vigorous tropical algae could withstand the cold and survive—and not just that, could spread. That was something extraordinary.

NARRATOR: He decided to find out what was going on. Back in the laboratory, he compared Caulerpa taxifolia with other specimens of the same family from around the world.

ALEXANDRE MEINESZ: I have a few specimens that I collected myself several decades ago in the Red Sea, and here is Tahiti, in Polynesia. They are all small, whatever depth they come from—not very long, not very wide and the runners are always very thin. So I realized straightaway that what was growing in the Mediterranean was something absolutely exceptional that had never been seen before.

NARRATOR: This new plant was bigger, tougher and more vigorous than any other specimen of Caulerpa, and it normally lived thousands of miles away in the tropics.

ALEXANDRE MEINESZ: It's a giant in comparison with what can be found in tropical seas. I realized that it was different from anything else in the world. I was absolutely astonished. It was something strange. I did some more research, but everything confirmed my first impression. It was an alien. Something abnormal, supernatural, was beginning to develop in the Mediterranean.

NARRATOR: It was growing so fast and dense that it was swamping the dark green native possidonia. There was something else, too. The coastal waters of the Mediterranean are normally home to some 600 species of animals and plants. Yet the seabed around the mysterious new algae was almost devoid of other marine life.

ALEXANDRE MEINESZ: I immediately felt that the whole Mediterranean was in danger. This was a very adaptable plant. It seemed able to alter the ecology of large areas of the sea.

NARRATOR: It seemed like something out of science fiction. What was a gigantic tropical algae doing flourishing in the temperate waters of the Mediterranean?

Yet on the surface, life went on as normal. Meinesz tried to raise an alarm, but no one was interested. He realized he needed better scientific evidence that the algae was damaging the sea's marine life. He took his concerns to a colleague along the coast in Marseilles. Charles-Francois Boudouresque is one of France's leading experts on Mediterranean underwater life.

CHARLES-FRANCOIS BOUDOURESQUE (University of the Mediterranean): Alexandre Meinesz telephoned me several times to say he'd made an incredible discovery. He asked me to come to Nice to see it. I said, "Yes, yes, but later." It took him a year to persuade me to come and see the colonies of Caulerpa taxifolia.

NARRATOR: When he saw it, Boudouresque was also shocked by the invasion. He immediately agreed to investigate whether the algae was harming the Mediterranean animal life. The animal he chose as a test case was the sea urchin, which lives on plants and is easy to observe in the laboratory. He set up a simple experiment.

CHARLES-FRANCOIS BOUDOURESQUE: Here is an urchin that has been fed on native Mediterranean algae. The mouth normally faces downwards. And we turn it over; we put it with its mouth facing upwards. We know that a sea urchin that is in good health takes about one minute to turn back over again to return to its natural position.

NARRATOR: Almost immediately the urchin began to put out little suckers, wave its spines and struggle to turn itself over. In less than a minute it had completed the maneuver.

CHARLES-FRANCOIS BOUDOURESQUE: There. What an athlete—it's a very good athlete.

NARRATOR: In another jar, Boudouresque had urchins fed exclusively on the new algae.

CHARLES-FRANCOIS BOUDOURESQUE: These urchins have been fed for a long time on Caulerpa taxifolia. We do the same experiment with them. We turn them over and measure the time they take to right themselves.

NARRATOR: The time they took to turn over crept up from two minutes, to five, to 20. Boudouresque suspected the urchins were finding the taxifolia inedible and were starving to death. After a month on an exclusive diet of taxifolia the turning-over time had reached 30 minutes. It soon became clear that some even preferred to die rather than eat the distasteful seaweed. The findings were very disturbing. If this new seaweed took over the Mediterranean, would other sea animals react in the same way? Would the whole food chain be disrupted?

What, the French researchers wondered, was the plant's secret weapon that stopped the urchins from eating it? Meinesz sent samples to a number of European labs specializing in plant toxins.

At the Max Planck Institute in Germany they began analyzing the chemical composition of the Caulerpa samples. The findings were unexpected. Many plants employ a chemical defense mechanism to ward off predators, but most use a variety of different toxins in relatively small quantities. The mysterious new algae turned out to be quite different.

GEORG POHNERT (Max Planck Institute): It is very special, because Caulerpa taxifolia is nearly entirely relying on one component that it is basing its whole chemical defense on. Usually plants use a multitude of different components that have all different target animals. Caulerpa taxifolia uses another strategy. It uses only one component, but this component is produced in a very high amount.

NARRATOR: It was the concentration of the toxin in the plant that was so unusual. The toxin is called "caulerpenine," and the concentration was higher than in any other algae Pohnert had ever analyzed.

GEORG POHNERT: The amount of toxin in the Mediterranean species is really surprisingly high for me as a chemist. It's a very powerful and very special defense mechanism. That might be why Caulerpa spreads in the Mediterranean very effectively.

NARRATOR: Pohnert discovered that although the toxin was not lethal to humans or animals, it made Caulerpa almost totally inedible. And if nothing would eat it, there was nothing to stop its advance. If it took over, the Mediterranean's animal life would be forced to flee or starve to death.

Alexandre Meinesz now believed he was dealing with not just any invasive plant, but an exceptionally harmful and vigorous organism. The algae continued to spread, growing at twice the speed of indigenous plants. And Meinesz was worried that the situation could rapidly get out of control unless something was done to stop it.

There was one hope. The colony of algae lay directly under the walls of one of Europe's most prestigious marine research and conservation organizations, the Monaco Oceanographic Museum. Meinesz felt sure the museum would help him. It would take money, resources and government involvement, but Meinesz was confident the museum would be able to persuade the French authorities to eradicate the algae before it spread further. He was in for a shock.

At the time, the museum was run by Professor Francois Doumenge, one of France's most influential marine biologists. For nearly a century, the Monaco museum has championed oceanographic conservation and preserved the riches of the sea in a series of palatial galleries.

Meinesz approached the museum with his concerns, but the museum's director had a very different view of the situation. He simply didn't believe the invasion of Caulerpa taxifolia was dangerous or unnatural.

FRANCOIS DOUMENGE (Former Director, Monaco Oceanographic Museum): The development of tropical species in the Mediterranean is an old story. Some species date back to the opening of the Swiss Canal and are well known, so there have been tropical species in the Mediterranean since the end of the 19th century.

NARRATOR: Doumenge argued that algaes like taxifolia are constantly moved around the world by sea currents and frequently lie dormant in the water for years, until a temperature change brings them to life.

FRANCOIS DOUMENGE: More and more, in my opinion, it is likely that there has always been a small and dispersed stock of dormant tropical species in the Mediterranean, and as the Mediterranean warms up and becomes more tropical, they start growing again. It's well known that the Mediterranean has experienced changes in level and temperature over time.

NARRATOR: Doumenge suggested Meinesz was worrying about nothing. The growth of the taxifolia was not a danger, merely a sign of the evolving character of the Mediterranean Sea.

FRANCOIS DOUMENGE: Eight to ten thousand years ago, the sea was 120 meters lower than it is now and three to five degrees cooler. So the Mediterranean should be seen as a basin which changes very rapidly on the geological time scale. Its current state is simply an intermediate state, a transitory phase. It's in this context that we should be looking at the Caulerpa.

NARRATOR: Doumenge passed on his thoughts to the French Ministry of the Environment, which breathed a sigh of relief. If the algae was not dangerous but part of a pattern of global change, there was not much the French government could be expected to do against such a natural occurrence. But not everyone was convinced.

Alexandre Meinesz was still alarmed by what he'd found and the impact it was having on the seabed. He'd spent years studying Caulerpa in the wild, and he was sure the invasion was not natural.

ALEXANDRE MEINESZ: I was sure I wasn't making a mistake. I had seen something very strange. I immediately draft a report that I sent to the top authority, but I did not even receive an acknowledgement. I thought, "Even if they don't believe me, they could have sent an outside expert to come and have a look, even just to come and check I wasn't talking nonsense." But no, absolutely nothing.

NARRATOR: Over the next 18 months the algae spread, as Meinesz had feared it might. In 1990, there were sightings at Cap Martin, about two and a half miles east of Monaco, and at Toulon, almost 125 miles in the opposite direction. By late 1991, there were some dozen patches of the algae dotted along the French Riviera.

ALEXANDRE MEINESZ: It confirmed all my fears. The algae was beginning to spread. I could no longer keep quiet. I absolutely had to tell the media to try to make the people aware of it. It was an alien. Nobody before had ever described anything which grew so large, vigorously and densely.

NARRATOR: Local newspapers picked up the story. There were alarming and lurid headlines: "The Green Menace," "Ecological Crime," "Mutant Algae." The plant now acquired a new name: "the killer algae."

By the early 1990s, with the press finally involved, the French Ministry of the Environment stepped in. It sent a research ship to the affected area of the Mediterranean to see what was going on. At long last, there was official recognition that something might be wrong. The man in charge of the government's research effort was marine biologist Thomas Belsher.

Belsher sent down divers to chart the taxifolia beds.

THOMAS BELSHER (Research Institute for Marine Development): The progress of Caulerpa taxifolia can be followed by an underwater video camera, which is a few meters above the seabed. And each time we see some Caulerpa, we mark it. This allows us to make accurate maps of the observations.

NARRATOR: Almost immediately, Belsher found that Meinesz, if anything, had underestimated the size of the infestation and the rate it was growing.

THOMAS BELSHER: Our estimate suggested the spread of the Caulerpa was greater than Alexandre Meinesz had observed at the same spot a few months earlier. It was obvious that this population of Caulerpa taxifolia was still there, and it was growing very rapidly.

NARRATOR: It was, as Meinesz had already observed, bigger, faster growing, and denser than any algae ever seen before. Belsher's maps revealed that the Mediterranean seabed was being transformed more quickly than at any time in recent history.

THOMAS BELSHER: We had never seen an algae introduced into a marine ecosystem that had grown so quickly. At the end of one or two years, instead of having a very colorful seabed we had nothing in some places except a green lawn, like a golf course.

NARRATOR: Entire marine ecosystems were being affected by the Caulerpa infestations. Researchers found that fish populations around the invasive taxifolia beds were falling measurably. In some places, half the fish had disappeared. Fish, like urchins, appeared to find the taxifolia too toxic to eat.

The French authorities, still only half-convinced this was a problem they could solve, commissioned a series of small-scale experimental eradications. It soon became clear that destroying the plant was going to be much more difficult than anybody had expected. Divers were sent down to dig up patches of algae by hand, but it was like trying to trim a football field with a pair of scissors.

ALEXANDRE MEINESZ: This algae is very difficult to eradicate. You can see that the roots are as fine as hair and have fruits that may give rise to new plants, so to eliminate it by hand you have to remove much more than what you see. You have to remove everything underneath as well, the mud, the sand, because there might be little bits not visible to the eye.

NARRATOR: They tried freezing it to death with blocks of dried ice, but their efforts were no match for the scale of the problem. They even tried sucking it up with an underwater vacuum cleaner. The trials quickly showed that it would take an army of divers many years to make an impact on the algae.

By 1994, new sightings showed that the taxifolia had spread even further. Yet there was something very puzzling about the way it was spreading. It was not just expanding into the neighboring seabed; it was leaping from one section of coast to another, establishing new colonies hundreds of miles apart.

Meinesz knew that if the authorities were to slow its spread, they needed to understand what lay behind this apparently erratic pattern of growth. But there were those who still believed there was nothing to worry about. The director of the Monaco museum, Francois Doumenge, continued to suggest Meinesz was overreacting.

FRANCOIS DOUMENGE: In my opinion, if we'd taken time to consider the problem, if we'd tackled it with greater scientific calmness and not instantly concluded that it was a catastrophe, we'd have realized there was not much to worry about.

ALEXANDRE MEINESZ: My feeling was that I had to continue my investigations. I had to continue to convince people of the problem. It was a question of time. Something could perhaps still be done. I had to study its biology more closely, study its dynamics more closely, in order to see whether there was still time to do something.

NARRATOR: Meinesz went back to the lab. He suspected the key to understanding the plant's erratic spread was knowing how it reproduced.

ALEXANDRE MEINESZ: What we wanted to know is how this species reproduces. You have to take a little bit of juice that is in this caliper, put it on the slide, and look at it under a microscope.

NARRATOR: The sticky juice inside the taxifolia contains microscopic particles called gametes or reproductive cells. These are normally male and female and act like sperm and egg.

ALEXANDRE MEINESZ: Theoretically, you should find two types of gametes, reproductive organs, inside the juice. The gametes are very small. They measure five microns. The male gamete is the same size as the female gamete, but there is a small difference, the female gamete has a red dot, a stigma.

NARRATOR: Meinesz studied slides of the taxifolia looking for the red dot that identifies the female gamete. He couldn't find a single female gamete.

ALEXANDRE MEINESZ: We looked in vain for female gametes on the specimens from the Mediterranean. There were no female gametes, no sexual reproduction.

NARRATOR: There could be only one explanation. The taxifolia in the Mediterranean was spreading, not through sexual reproduction, but by a process known as vegetative reproduction. It's a form of cloning. It was an important breakthrough that finally made sense of the strange spread of the taxifolia.

It meant that any tiny fragment of the algae separated from the main plant contained all the genetic material necessary to grow an exact replica of the parent plant. It's as if a piece of human hair or a flake of skin dropped on the ground could grow into a complete human being. Meinesz now realized that it would only take a tiny fragment of the taxifolia, picked up by the anchor of one of the thousands of boats that crisscross the sea, to start a new colony of plants hundreds of miles away.

By 1997, a new map of the colonies of the algae seemed to confirm this hypothesis. It had jumped further along the coasts of France and Italy; it had even leapt across to the coast of Croatia. Eight years had passed since Meinesz first raised the alarm. Now, nowhere in the Mediterranean seemed safe.

ALEXANDRE MEINESZ: It was really sad to see, because it's a question of time. Time matters in these affairs. When a species begins to invade you have to act now.

NARRATOR: But no one acted, and Meinesz could only watch in horror as the weed continued to spread. Around this time, a dramatic discovery in Switzerland would soon throw new light on the algae's origins and confirm Meinesz's fears that there was something very unnatural about this plant.

It happened here at the University of Geneva. Olivier Jousson is a specialist in DNA sampling. He realized the only way to prove whether the gigantic taxifolia in the Mediterranean was a natural invasion was to trace its origins. If he could match its DNA to the DNA of any tropical taxifolia, then the theory that it had naturally drifted in from the tropics was probably right.

OLIVIER JOUSSON (University of Geneva): I realized that the main problem with Caulerpa was that nobody knew where it had come from.

NARRATOR: He set about processing dozens of samples of taxifolia from all over the world, including the Red Sea and areas of the Pacific. Nothing matched. Each time, the DNA fingerprint was different from the Mediterranean strain. It was a mystery. Eventually there was only one strain left to try. It was a perfect match. But this was not a wild plant; it had been bred by humans. It was a sample of Caulerpa taxifolia taken from an aquarium tank.

For years a very peculiar strain of Caulerpa taxifolia has been used to decorate tropical fish tanks. It appeared that it was this human-bred, artificial strain, which had escaped into the Mediterranean.

OLIVIER JOUSSON: The fact that these two are identical, in our opinion, means that they are the same plant. The strain that exists in the Mediterranean and the strain that exists in aquaria are the same.

NARRATOR: Jousson's discovery proved beyond a reasonable doubt that the taxifolia in the Mediterranean had not drifted in from the tropics. Monaco's argument that the appearance of taxifolia was part of a natural cycle of change in the sea did not hold up. It wasn't long before people also realized that if the findings were right, the most obvious source of the alien invasion was the Monaco Oceanographic Museum itself.

The museum was known to have had taxifolia in its tropical tanks and was also directly above the site of the first known infestation. Yet to suggest that the museum was even unwittingly responsible carried huge political and scientific implications. It meant the institute had somehow unknowingly allowed material from its aquarium tanks to get into the sea. Even worse, the most likely time for all this to have happened was in the early 1980s when the museum had been run by a man with an international reputation for marine research, Jacques Cousteau.

For years he'd been the father of French marine biology, a hero of marine conservation. The irony was that to accuse the Monaco Museum of even accidentally releasing a rogue seaweed into the sea, was to hold some of the most famous names in marine conservation responsible for what many now regarded as an ecological disaster. The museum flatly denied any link between the taxifolia in its tanks and the taxifolia below its walls and questioned the validity of the DNA findings.

FRANCOIS DOUMENGE: I think that the tests that were performed didn't use either the safest or best-known methods. What we need for an accurate answer is much more detailed, much finer genetic studies, using a much bigger range of samples than was practical before.

NARRATOR: But Doumenge was in the minority. Even Jacques Cousteau, when he later found out about the issue, told the French Minister of Environment that there might be cause for concern.

But with so much taxifolia in the sea, assigning blame seemed a waste of time. Scientists now realized that wherever the aquarium breed had come from, they were dealing with an extremely invasive plant. It was also remarkably adaptable. Unlike tropical taxifolia, it had a new and distinctive DNA fingerprint and could survive in winter water temperatures around 55, or 13 degrees Celsius.

ALEXANDRE MEINESZ: I ask myself a question: "How can this algae which only lives in the tropics where it's always 20 degrees, withstand winters when it's 13 degrees? How could it stay alive?"

NARRATOR: The search for an answer lay in tracing the aquarium plant to its original source. The trail led from Monaco to an aquarium in Stuttgart, Germany. Here, during the 1970s, the staff made a curious discovery. At the time, people everywhere had been trying to find a plant that could be used to decorate tropical fish tanks. The world's leading aquariums imported wild specimens from the four corners of the globe, but nothing seemed to survive in the artificial environment of a tank.

But then, in the Stuttgart aquarium, something unexpected happened. A newly imported strain of wild Caulerpa taxifolia from the Pacific suddenly blossomed and thrived. It became the aquarium's wonder plant. At the time no one asked how, or why, it had flourished so rapidly. Now they did.

ALEXANDRE MEINESZ: The question of the nature of this algae gave me a lot of food for thought, and there are only two hypotheses. First hypothesis: someone selects a bunch of Caulerpa in the wild, which is slightly abnormal, more resistant to the cold, and it is this one that is grown in an aquarium and finds its way into the Mediterranean.

NARRATOR: In other words, a collector in the 1970s, had, by accident, selected an unusually big and robust sample of the plant in the wild, and it was this exceptional plant which had been grown in the Stuttgart aquarium. But there was also a second possibility.

ALEXANDRE MEINESZ: The second hypothesis: something happens in the aquarium to modify the plants. For some reason there is a change in its genetic structure, a mutation, a change in the chromosomes. It could be one of several things.

NARRATOR: Aquarium tanks use chemicals and lights to artificially recreate the natural balance of the sea. Could this manmade brew have caused the original wild strain to change or mutate into a more invasive plant than its wild cousin?

To this day no one has solved the mystery. And the discovery was rapidly overtaken by a new concern. Throughout the '80s and '90s, the German-bred algae was sent to aquariums around the world. It had become the most popular aquatic plant on earth. It was everywhere. If it could escape from one tank and survive, it could escape from others. And if it could flourish in the Mediterranean, it could flourish in dozens of other seas. The super algae that Alexandre Meinesz had warned France about 12 years before was now, potentially, a global problem.

California, with a huge trade in exotic plants, was always a likely victim. Aware of the growing Mediterranean problem, the United States listed Caulerpa taxifolia as a noxious weed and banned its importation. But aquariums and millions of tropical fish hobbyists could still buy existing supplies. It was only a matter of time before it escaped into the wild. And in June of 2000, that's just what happened. Caulerpa taxifolia was found in a coastal lagoon in southern California.

ROBERT HOFFMAN: It could have been simply a case of where the individual was cleaning his aquarium in his front yard, in the street. And he had the algae in the aquarium, and pieces of it floated down the gutter, got into the storm drain and then were just discharged into the lagoon, because there is a storm drain outlet right here, very close to where the infestation is.

NARRATOR: To avoid the disaster overtaking the Mediterranean, the officials in California knew they had to act fast. Within days, they'd settled on a radical campaign of eradication. The chosen weapon was chlorine, which kills everything in its path.

The chlorine is pumped down through a pipe from tanks on the surface into a tarpaulin, which has been spread over the algae and held down at the sides with pegs and sandbags. Everything under the tarp is killed: plants, fish, crustaceans. It's a price California is willing to pay.

GREIG PETERS: No matter what level, how harsh the chemical response is, if we're effective, it's hard to believe that that could be as bad as not being effective and having our whole coastline smothered by this algae.

NARRATOR: The chlorine, with an approximate strength of household bleach, acts almost immediately. Within hours, the taxifolia is dead. It's an extreme solution and expensive—more than a million dollars a year—but it seems to be working. In early 2003, no new growth of taxifolia was found. It's encouraging, but the lagoon will still have to be monitored for many years.

But the infestation in the Mediterranean has grown too large for this solution. After 15 years, the algae has won. Poison is simply impractical, and the scale of the destruction of wildlife would be completely unacceptable.

In France, some small underwater reserve areas have been identified that will be patrolled each year. If Caulerpa is discovered in these rich marine parks, it will be pulled out by hand.

But Alexandre Meinesz believes there is only one way to defeat this weed. It's more controversial than poison, it's more drastic than most people will accept. It's a tiny tropical slug that kills taxifolia as it eats it. At the University of Nice, Meinesz stumbled on it by accident.

ALEXANDRE MEINESZ: I heard from an American professor in Florida, who told me there was a slug that fed exclusively on Caulerpa. To begin with, I didn't take him very seriously. I couldn't believe that these little slugs could make much difference to the enormous amount of Caulerpa we've got here. Then, by accident, we imported some of them in a bunch of Caulerpa from the Caribbean. So we began studying them and looking at their potential as a biological weapon against Caulerpa taxifolia, and we have a few hopes.

NARRATOR: The slug is unique in producing an enzyme that enables it to eat the plant and neutralize its toxin.

ALEXANDRE MEINESZ: What is extraordinary is the way these slugs eat the Caulerpa. They don't chew it as we eat salad. They make a small hole and suck out the juice.

NARRATOR: It's like a vampire, sucking out the juice and leaving a dying husk. Meinesz would like to release thousands of these tropical slugs into the sea to attack the taxifolia beds. While they could never eradicate the existing Caulerpa, he believes they could slow down the spread. But it's not nearly as straightforward as it sounds. There are two problems. The French authorities are understandably wary of introducing yet another alien species into the Mediterranean and have so far refused to fund the research. Yet Meinesz is sure the slug has evolved such a specialized and exclusive dependence on Caulerpa, it won't attack anything else.

ALEXANDRE MEINESZ: All the studies we've done tell us that there would be no danger if these little slugs were released into the Mediterranean.

NARRATOR: The other problem is that this little slug from Florida can't survive in the deeper, colder, Mediterranean waters. Meinesz is now calling on the world's scientists to find a related slug that can tolerate the lower temperatures and munch the taxifolia problem away. In the meantime, no temperate ocean is safe, as Australian Broadcast News reports a new infestation.

REPORTER: South Australia's $500,000,000 fishing and aquaculture industry is under threat, and the government has declared war.

NARRATOR: It was actually Australia's second Caulerpa attack. But this one was much bigger than California's and harder to handle. The government quickly started testing methods to control it. Huge quantities of salt would kill the weed, but the infestation was so large, they worried there wasn't enough salt in all of Australia to work.

They also considered something more drastic: pumping copper sulfate into the water. It would kill every living thing and close the lagoon for two years. While copper sulfate may well prevent the weed from moving into the open ocean and threatening the fishing industry, for many Australians, it's just too controversial. So no decision has been made. For now, they're trying to stem the spread by pulling the taxifolia out by hand.

Fifteen years after it was first discovered, Caulerpa taxifolia now grows in nine countries on four continents. The problem is entirely manmade. Today, millions of tropical fish hobbyists still decorate their aquariums with this brightly colored but dangerous plant. Improper disposal of even a tiny fragment of Caulerpa taxifolia can start the next infestation as this green monster continues to spread throughout the world's oceans.

It's not just this invasive plant that we need to worry about, other alien species are attacking habitats in waters and on land around the world. Find out more on NOVA's Website, at or America Online, Keyword PBS.

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Deep Sea Invasion

Written & Directed by
Nick Davidson

Narrated by
Jeremiah Kissel

For Horizon

Ron Orders

Production Assistant
Sascha Olofson

David Baillie
Bob Cranston
Jean-Marc Bour

Sound Recordists
Tony Cogger
Maggie Ellis

Edited by
Rory Ferguson Martin Sage

Time Lapse Photography
Tim Shepherd


Translation Voices
Emmanuel Bonami
Olivier Deslandes
Pierre Monbouche
Peter Newman
John Pierre Steck

Production Manager
Jacqui Timberlake

Production Coordinator
Sarah Jobling

Unit Managers
Alex Barraki
Fiona Reid

Executive Editor, Horizon
John Lynch

Series Editor, Horizon
Bettina Lerner


Produced by
Nancy Linde

Associate Producer
Marty Johnson

Edited by
Stephanie Munroe

Online Editor
Ed Ham

Mark Kueper

Audio Mix
Heart Punch Studio

Archival Material
Ontario Power Generation
USDA Forest Service
SBS Insight

Special Thanks
Alan Millar
Nature Conservancy
Gene Colling

NOVA Series Graphics
National Ministry of Design

NOVA Theme
Mason Daring
Martin Brody
Michael Whalen

Post Production Online Editor
Mark Steele

Closed Captioning
The Caption Center

NOVA Administrator
Queene Coyne

Jonathan Renes
Diane Buxton

Senior Researcher
Ethan Herberman

Production Coordinator
Linda Callahan

Unit Manager
Holly Archibald

Nancy Marshall

Legal Counsel
Susan Rosen Shishko

Post Production Assistant
Patrick Carey

Associate Producer, Post Production
Nathan Gunner

Post Production Supervisor
Regina O'Toole

Post Production Editor
Rebecca Nieto

Producers, Special Projects
Lisa Mirowitz
Stephen Sweigart

Coordinating Producer
Laurie Cahalane

Supervising Producer
Lisa D'Angelo

Senior Science Editor
Evan Hadingham

Senior Series Producer
Melanie Wallace

Managing Director
Alan Ritsko

Executive Producer
Paula S. Apsell

A cineContact Production for BBC

Additional program material © 2003 WGBH Educational Foundation

All rights reserved

Deep Sea Invasion

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.


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