Killer Algae

"Once in a while a single example has the power to focus public attention on a serious problem, and this is one of them. The Caulerpa story, told vividly by Alexandre Meinesz and made available in English by Daniel Simberloff's translation, reads like a science-fiction horror story. It calls our attention to the growing worldwide problem of invasive species, the stealth destroyers of the environment."—Edward O. Wilson

"Meinesz's fight against C. taxifolia—and against the arrogant ill-informed oficials who allowed it to prosper—may be a lost battle, but his combat journal is enormously valuable. We will never have any such well-documented record of how the gypsy moth, the whelk tingle, or the house sparrow established their beachheads and rolled on to conquest."— from the foreword by David Quammen

Websites about Caulerpa Taxifolia and other invasive species

The Caulerpa taxifolia unofficial website—a seaweed unlike any other.

More photographs of Caulerpa taxifolia taken by Meinesz.

Simulations of Caulerpa taxifolia evolution in the north Mediterranean Sea.

Scientific papers and documents dealing with the alga Caulerpa taxifolia introduced to the Mediterranean.

Invasive species resources

Bioinvasions: Stemming the Tide of Exotic Species at the World Resource Institute.

Invasive species section of the National Biological Information Infrastructure site (USA).

The Institute for Biological Invasions at the University of Tennessee

Biological Roulette—an alien species page at the Smithsonian Institution/Ocean Planet (USA).

Nonindigenous Aquatic Species information resource at the United States Geological Survey.

Invasive Plants of Canada project.

Australia's Centre for Research on Introduced Marine Pests.

The Group on Aquatic Alien Species (Russia)

Other well-known invaders

The Northern Snakehead Fish (Maryland DNR Fisheries Service)

The Asian Longhorned Beetle (United States Department of Agriculture).

The European green crab (Smithsonian Environmental Research Center).

The Gypsy Moth in North America(Forestry Sciences Laboratory at West Virginia University).

The Amazing Story of Kudzu (University of Alabama Center for Public Television & Radio).

The Zebra Mussel Page (United States Geological Survey).

An excerpt from
Killer Algae
by Alexandre Meinesz


In the early 1980s, the curator of the tropical aquarium at Stuttgart, Germany, noticed the exceptional properties of a beautiful green alga, Caulerpa taxifolia, used as decoration in the presentation of multicolored tropical fishes. In contrast to other algae, it does not wither, it grows with astounding vigor, it resists cool water temperatures, and it serves as a secondary food source for herbivorous tropical fishes. Specialists quickly learned about these qualities, and public aquaria acquired cuttings.

This is how it arrived at the Oceanographic Museum of Monaco, where it was cultivated beginning in 1982. Two years later, the alga was discovered in nature, under the windows of this celebrated building. At that time, the beautiful stranger occupied only a square meter of Mediterranean bottom. Six years later, the alga was noted on the French coast five kilometers from Monaco; its detrimental impact on coastal ecosystems was deplored. The alga grows everywhere, from the surface to the lower limits of underwater vegetation. It grows as well in front of capes swept by storms and currents as on the soft bottoms of sheltered bays, on the polluted mud of harbors as on stretches of bottom with a diverse flora and fauna. Highly toxic, it barely interests herbivores; they have not hindered its spread. It is thus growing unrestrained, covering and then eliminating many plant and animal species. A new equilibrium is reached when the alga forms a dense, uniform carpet that persists from year to year.

After having selected it for aquaria from among numerous imported algal species, after having dumped it into the sea, humans fostered its dissemination in nature. Yacht anchors and fishing gear have carried it from anchorage to anchorage and from harbor to harbor, sometimes over great distances. The Italian and Spanish coasts were reached by 1992, that of Croatia by 1995. By late 1997, ninety-nine invaded sites totaling more than 4,600 hectares have been inventoried.



Rocky substrates covered by Caulerpa taxifolia (Cap Martin, 26 meters with gorgonians).

No one has ever been killed by Caulerpa taxifolia, known as the "killer alga." For, contrary to what its media nickname might suggest, this prolific alga is primarily an ecological threat. All relevant research indicates an unlimited spread. Its control is more difficult every year, and its eradication, envisaged at the beginning of the invasion, can now be classed only as a utopian dream. The introduction of this dangerous alga therefore threatens to initiate a profound disruption of the coastal Mediterranean environment. The story of the "killer alga" has, unfortunately, just begun.

How did we reach this point? When the first scientific publications confirmed the threat, the alga was, contrary to any reasonable expectation, defended by other scientists who tried to argue that its appearance was a natural event. This was the beginning of a long, fantastic polemic. The affair is even stranger because the place where the alga was introduced to the Mediterranean is truly incongruous--the principality of Monaco, a state with one of the highest standards of living. This is far from the Polish forests devastated by acid rain, far from the Aral Sea dried up by diverting water, far from the third world where overpopulation engenders overexploitation of natural resources. More remarkably, the first signs of the invasion were observed just in front of a palace of the sea, a landmark of marine biology: the Oceanographic Museum of Monaco. This prestigious palace, built between 1899 and 1910 by Prince Albert I of Monaco (a highly erudite and competent oceanographer), was directed from 1957 through 1988 by Commander Jacques-Yves Cousteau, a person emblematic of the sea.

The polemic has been heated, fed by the defense of many different interests. It was able to break out because key scientific and government authorities were lax and because of disdain for a problem that does not directly threaten human health. An abundance of communications on this affair masks inadequate knowledge and a failure of government experts. The object of byzantine debates between scientists, government experts, public figures, and the media, this sterile controversy slowed the recognition of the threat. The threat was long underestimated while the time during which it might have been successfully contained dribbled away. The alga grew inexorably, and it still grows, disturbing the marine environment . . . and the human intellect.

A university researcher who specializes in Caulerpa, and a diver devoted to defending marine life, I was the first to sound the alarm in 1989. An actor in or observer of all the intricacies of this affair, I encountered deplorable actions in the face of a concrete threat to biodiversity, at a propitious time in countries in which everything could have been undertaken to allow a rational and rapid mastery of the situation. Having taken it upon myself to alert the authorities and then the media about the imminent threats, I am undertaking in this book to describe the years of battle that I have subsequently lived. This fact explains the personal tone of this report.

Of course, recalling facts and activities will arouse in the reader some remorse and much revulsion and indignation. But this first history of the killer alga is much more than the simple, lively chronicle of a trivial ecological accident. It is also an analysis of the social and political mechanisms that raised obstacles to the successful management of a potentially grave environmental threat. The passions that were unleashed, often extremely heated, were the result of a failure of our institutions to function properly. This account can also be read as an example of the conflicts in scientific and administrative hierarchies with respect to the "affairs" that have shaken up our industrialized countries at the end of this century and in which scientists very quickly played the role of sentinel; they detected the threat and gave the alarm. But many obstacles delayed the decisions that would have to have been made to avoid the dreadful sequels that we now observe. Though the alga is not a killer, the damage caused to our environment is already manifest, and the ecological consequences for the fauna and flora--and finally for humans who exploit them--can be very grave. The years of inaction produce and will continue to produce, in every case, an enormous cost for society.

A tropical sea slug, Elysia subornata, eating Caulerpa taxifolia. This species is a hoped-for biological control agent.
The first six chapters of this book present, with details and references, the chronology of the events and their socio-political context, from the introduction of the alga at Monaco through the delayed recognition of its harmful nature. The seventh and last chapter reflects on the three causes underlying all the incoherence and negligence that characterized this affair: scorn for biodiversity at the decision-making level, the decline of the sciences of nature, and the evolution of the ways in which scientific information is communicated. The seventh chapter also locates the invasion of Caulerpa taxifolia amidst the swelling tide of exotic species invading terrestrial, freshwater, and marine habitats all over the earth, a phenomenon that now ranks second among global threats to biodiversity.

As beautiful as a flower, Caulerpa taxifolia still poses many scientific questions. It has aroused passions in people with diverse interests. Some actors in the black tale of this "natural history" displayed an incomprehensible attitude, lamentable for people of their rank, given the responsibility that society has given them. The alga has thus become the sort of evil flower that Baudelaire must have glimpsed when he wrote his prescient poem:

Both of you are discreet, dim, shadow-ridden:
Man, none has plumbed your soul's abyss; and, sea,
No one has pierced your wealth's dark mystery,
So jealous, you, to keep your treasures hidden!*

*"Man and the Sea," in Charles Baudelaire, Selected Poems from "Les Fleurs du Mal": A Bilingual Edition, trans. Norman R. Shapiro (Chicago: University of Chicago Press, 1998), 25.



A winter dive, 1992

February. The water was at its coldest, 12°C at the surface, 13°C underwater. It always takes a little courage to enter the gray sea, whipped by surf, with the rays of the sun too oblique to penetrate deeply. One first feels the slap of freezing water in the face and then the torture of its infiltration beneath the neoprene dive suit. Then one recovers while shaking a bit and is suddenly plunged into another world. I will never tire of the everyday features of life underwater: the behavior of a fleeing fish, the winter colors of multicolored algae, the mysterious clicks of molluscs, fishes, and crustaceans glimpsed through the turbulence of the two lines of bubbles emanating from the regulator.

The winter storms tear up or shred anything fragile between the surface and five meters; the Caulerpa "sink." The first fronds are shrivelled, broken, sparse. But at ten meters all seems calmer; a green carpet, thick and strong, covers rocks and sand. The alga is beautiful, it undulates under the attenuated influence of the swells. But I see too much of it, I have already seen too much of it. I see it every time I dive in this spot. I know that lower, to the right, to the left, it is the same. I know that I can swim over the Caulerpa prairies until I exhaust my air supply. It is everywhere. In three months, it will reawaken, proliferate, stretch out to cover and suffocate. I am enraged. Then I gather some, I shove it under the mask strap, under the weight belt, under the lifejacket, I sew a collar of it, I adorn myself with it, I am quickly encircled with garlands of Polynesian ferns! I have them all over, I am completely green.



Area of sand covered by Caulerpa taxifolia (Cap Martin).

My teammate imitates me. We resemble the French cartoon characters Dupond and Dupont who, in Tintin comic books, have a green beard and green hair that never stop growing. Mockery in the face of our impotence against this supernatural prairie, so beautiful, so gentle, but also so deceitful, so cruel for the other algal prairies, for coastal underwater life of the Mediterranean. No, we are not stricken by dive narcosis, the terrible affliction that each year maddens and kills many divers; it is simply a collective letting off of steam on the subject that haunts our dreams. We bathe ourselves in Caulerpa, we roll around in it. We laugh, it is good for us.

It is time to surface, to go through the stages of decompression, to return to reality. The green monsters rise from the bottom, pick off shreds of green flesh that sink in the current. Surface! It is now necessary to confront other hydras, other evils.


Copyright notice: Excerpted from pages xi-xiv and 95-96 of Killer Algae by Alexandre Meinesz, published by the University of Chicago Press. ©1999 by the University of Chicago. All rights reserved. This text may be used and shared in accordance with the fair-use provisions of U.S. copyright law, and it may be archived and redistributed in electronic form, provided that this entire notice, including copyright information, is carried and provided that the University of Chicago Press is notified and no fee is charged for access. Archiving, redistribution, or republication of this text on other terms, in any medium, requires the consent of the University of Chicago Press.

Alexandre Meinesz
Killer Algae
Translated by Daniel Simberloff and with a Foreword by David Quammen
©1999, 376 pages, 8 color plates, 5 line drawings, 7 maps
Cloth $25.00 ISBN: 0-226-51922-8
Paper $16.00 ISBN: 0-226-51923-6

For information on purchasing the book—from bookstores or here online—please go to the webpage for Killer Algae.

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