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Deep Sea Invasion

Chronology of an Invasion

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Bred for its beauty, fast growth, and tolerance for cold, the "aquarium strain" of Caulerpa taxifolia, a bright green seaweed with fernlike fronds that is used to decorate saltwater aquariums, "escaped" from human control in the 1980s and has spread like a cancer through the Mediterranean, overwhelming native species and habitats. In this time line, written by Alexandre Meinesz, the marine biologist who has fought for years to warn authorities in France and elsewhere of this growing menace, follow the disquieting trajectory of this "killer alga" as it colonizes new waters around the world. Unless otherwise noted, "the alga" and "C. taxifolia" refer to the aquarium strain.


A clone of Caulerpa taxifolia that is resistant to cold is observed in the tropical aquarium at the Wilhelmina Zoo in Stuttgart, Germany. It is distributed to the public aquarium in Nancy, France, as well as to aquariums at the Oceanographic Museum of Monaco and the Oceanographic Institute of Paris.


A square yard of C. taxifolia grows in the Mediterranean beneath the Oceanographic Museum of Monaco.


The acclimatization of the alga to the Mediterranean is discovered by Alexandre Meinesz, who expresses his concerns to the Monacan and French authorities.

Two and a half acres of C. taxifolia now grows in front of the Oceanographic Museum of Monaco.


July—The alga turns up in France at Cap Martin, three miles east of Monaco. An initial newspaper article appears, and Meinesz sends his first letters of concern to the French authorities. In the press, the directorate of the Oceanographic Museum of Monaco minimizes the threat.

September—The alga is found near Toulon, 93 miles west of Monaco. Off Monaco and at Cap Martin, the alga covers over seven acres.


January—Fishermen of Alpes-Maritimes, the French district that surrounds Monaco, drag up C. taxifolia in nets set more than 330 feet deep.

February—The journal Oceanologica Acta accepts an article by Meinesz and his colleague Bruno Hesse describing the risks associated with the invasion of the introduced alga. The article is published a few months later(1).

April—Meinesz submits to the French Ministry of the Environment and the Secretariat of State for the Sea a file listing studies to be urgently undertaken. The director of the Oceanographic Museum of Monaco turns to the press to deny the Monacan origin of the alga and to proclaim its benefits.

May—Meinesz makes his initial contact with IFREMER, the French Research Institute for Exploitation of the Sea, resulting in no action.

July—IFREMER and the directorate of the Oceanographic Museum downplay the problem.

Autumn—The alga spreads at Monaco and Cap Martin (74 acres in total). It is found at Agay Bay, halfway between Monaco and Toulon, and at Le Lavandou, about 25 miles east of Toulon.

December—C. taxifolia appears at Saint-Cyprien (Pyrénées-Orientales), over 200 miles west of Monaco. Scientists from the Universities of Nice, Marseilles, Pisa, and Trent organize a round table, at which they call for eradication of the alga.


January—The alga is discovered at Saint-Cyr-les-Lecques (Var), 125 miles west of Monaco between Toulon and Marseilles.

February to October—Four commissions are created, and four French government ministers come to the Côte d'Azur. But no decision is made to control the algal spread.

June—The alga has reached Imperia, Italy, 25 miles east of Monaco.

September—The alga appears in the Balearic Islands of Spain.

December—The European Union finances the first research ever conducted into the C. taxifolia problem, funding 125 researchers in 25 laboratories.

Late 1992—The alga has invaded at least 28 sites between Menton (near the French border with Italy) and Toulon. More than 1,000 acres are more or less infested.


The alga spreads in Italy, including off Liguria, Leghorn, Elba, and as far south as Sicily.


The alga is discovered in Port-Cros National Park, on islands off the coast of southern France 62 miles west of Monaco.

December—The scientists assigned to study the problem issue the "Barcelona Appeal," which argues that the spread of C. taxifolia constitutes a major threat to Mediterranean ecosystems.

Late 1994—By this time, at least 38 sites have been invaded, with 3,700 acres infested. The alga is spotted at two sites in Croatia, more than 600 miles east of Monaco in the Adriatic Sea.


Late 1995—Monacan researchers publish an article in a journal of the French Academy of Sciences trying to prove that the alga came from the Red Sea and is innocuous(2).


July—Meinesz and marine biologist Charles-François Boudouresque publish a counter-article in the Academy of Sciences journal, arguing that certain results of the Monacan researchers are incorrect(3).

September—The European Community finances a second research program.

Late 1996—By this time, at least 68 sites have been invaded and 12,350 acres infested.


March—Workshop of the French Academy of Sciences with 50 specialists. Ambiguous conclusions are drawn concerning the origin and danger presented by the alga, but strong recommendations are made to attempt to prevent dissemination and to control the spread.

March—Meinesz publishes the first edition(4) of his book, which is published two years later in the U.S. as Killer Algae: The True Tale of a Biological Invasion (University of Chicago Press, 1999).

September—At the Third International Workshop on C. taxifolia at Marseilles, researchers ask French Prime Minister Lionel Jospin to establish a strategy for prevention and control.


March—At the United Nations Environmental Program's "Workshop on the Caulerpa Species Invasive in the Mediterranean," held at Heraklion, Crete, representatives unanimously conclude that the alga constitutes a major threat to Mediterranean ecosystems and recommend that all affected countries establish a strategy to prevent dissemination and curb the invasion.

October—The first published study of C. taxifolia genetics reports that all aquarium strains and colonies from the Mediterranean are genetically the same(5).


January—Motion introduced to French Chamber of Deputies calling for inquiry into the polemic surrounding C. taxifolia and the slow response of the national government to the spread of the alga.

April—The U.S. Department of Agriculture adds the aquarium clone of C. taxifolia to the Federal noxious weed list.


January—The alga is found for the first time in the southern Mediterranean, in the seas near Sousse, Tunisia.

June—The alga is identified in California waters off San Diego and Los Angeles. Researchers monitor 11,300 square feet of the alga in San Diego's Agua Hedionda lagoon.

November—The scientific journal Nature publishes an article on the genetics of a large collection of C. taxifolia from around the world(6). The C. taxifolia identified in California is genetically the same as the strains from the Stuttgart aquarium and from the Mediterranean. Researchers discover that the aquarium strain is genetically close to a native strain of C. taxifolia that occurs off the Australian coast at Moreton Bay, which appears to be the original source of the alga that was cloned to form the aquarium strain.


January—Divers discover the invasive strain of C. taxifolia near Sydney, Australia, hundreds of miles from the native strain at Moreton Bay.

September—The Governor of California prohibits the sale, possession, and transport of C. taxifolia throughout California.

December—An article by Meinesz et al examining the spread of C. taxifolia in the Mediterranean shows that the alga has invaded 50 square miles of seabed along nearly 120 miles of coast(7). Researchers and others have now identified over 100 independent colonies in the sea.


January—An international meeting on C. taxifolia is held at San Diego, where the eradication of the alga is well under way under the auspices of the Southern California Caulerpa Action Team.

Spring—C. taxifolia turns up near Adelaide, hundreds of miles to the west of Sydney in southern Australia.

September—C. taxifolia arrives in Sardinia, the largest island in the Mediterranean Sea.

Autumn—A survey of San Diego's lagoon reveals no C. taxifolia.


February—A preliminary report on the situation of C. taxifolia along the coasts of southern France shows a rapid expansion, with 40 new colonized areas since December 2000 and more large, concentrated areas resulting from the fusion of numerous smaller zones.


1. Meinesz, A. and B. Hesse. 1991. "Introduction and Invasion of the Tropical Alga Caulerpa taxifolia in the Northwest Mediterranean." Oceanologica Acta, Vol. 14, No. 4: 415-26.

2. Chisholm, J., J. Jaubert, and G. Giaccone. 1995. "Caulerpa taxifolia in the Western Mediterranean: Accidental Introduction or Migration from the Red Sea." Comptes Rendus de l'Académie des Sciences (III, Sciences de la Vie), Vol. 318: 1219-26.

3. Meinesz, A. and C.-F. Boudouresque. 1996. "On the Origin of Caulerpa taxifolia." Comptes Rendus de l'Académie des Sciences (III, Sciences de la Vie), Vol. 319: 603-13.

4. Meinesz, A. Le Roman Noir de l'Algae "Teuse": Caulerpa taxifolia Contre la Méditerranée, ©Éditions Belin, 1997.

5. Jousson, O., et al. 1998. "Molecular Evidence for the Aquariologic Origin of the Green Alga Caulerpa taxifolia Invading the Mediterranean Sea." Marine Ecology Progress Series, Vol. 172: 275-80.

6. Jousson, O. et al. 2000. "Invasive Alga Reaches California." Nature, Vol. 408: 157.

7. Meinesz, A., et al. 2001. "The Introduced Green Alga Caulerpa taxifolia Continues to Spread in the Mediterranean. Biological Invasion, Vol. 3: 201-210.

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Diver with clump of algae

In 1984, when the "killer algae" were first noticed in nature, divers easily could have hand-pulled all of the seaweed up, nipping in the bud what has become an explosive bioinvasion. Regrettably, this was not done, and the algae have now propagated throughout the Mediterranean.

Map 1 (first outbreak)

The aquarium strain of C. taxifolia apparently first took root in the sea below the Oceanographic Museum of Monaco in the early 1980s.

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Map (1993)

By 1993, the aquarium seaweed had spread its tentacles as far west as Mallorca and as far east as Sicily.

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Map (1994)

The ease with which C. taxifolia can travel to and gain a foothold in new areas was seen by the end of 1994, when it had turned up in the Adriatic Sea, more than 600 miles from Monaco.

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Meinesz profile

Early on Alexandre Meinesz foresaw the perils of procrastination in taking steps to halt the spread of C. taxifolia, but for years his warnings fell on deaf ears.

San Diego lagoon cordoned off

Soon after discovering C. taxifolia in San Diego's Agua Hedionda lagoon, U.S. researchers cordoned off the affected area. The alga was eventually eradicated there.

Diver over thick bed

To keep C. taxifolia from getting out of control, as it has in the Mediterranean (above), coastal authorities around the world must vigilantly watch for the algae's appearance in their waters.

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.

This time line was adapted and updated from one that appeared in Killer Algae: The True Tale of a Biological Invasion (University of Chicago Press, 1999).

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