Caulerpa taxifolia
Encyclopedia
Caulerpa taxifolia is a species of seaweed
, an alga of the genus
Caulerpa
. Native to the Indian Ocean
, it has been widely used ornamentally in aquariums. The alga has a stem which spreads horizontally just above the seafloor, and from this stem grow vertical fern-like pinnae, whose blades are flat like yew
, hence the species name "taxifolia" (the genus of yew is "Taxus
"). The alga produces a large amount of a single chemical that is toxic to fish and other would-be predators. This is in contrast to other plants which produce a variety of toxins, but in reduced amounts.
It is one of two algae on the list of the world's 100 worst invasive species compiled by the IUCN Invasive Species Specialist Group.
It is thought that the seaweed was accidentally released into coastal waters of the Mediterranean Sea
just below the Oceanographic Museum of Monaco in 1984. Ten years later, Caulerpa had grown to cover 7400 acres (29.9 km²), preventing native plants from growing and leading to the nickname "Killer Algae". Caulerpa overgrows the seabed and disrupts the food cycle dependent on the native plant life. The plant began to spread between ports along the Mediterranean coast. C. taxifolia has been discovered off the coasts of Australia
and the United States
, though none of these encroachments have been anywhere near the scale of what is happening in the Mediterranean.
For several years, the origin of the species was unclear. Marine biologist
Alexandre Meinesz first discovered the plant in the 1980s, and requested the help of the Monaco Oceanographic Museum, which sat right next to the first known C. taxifolia patch. However, the director of the museum argued that this invasion probably happened naturally, the result of ocean current
s carrying a tropical
species into the area. Bickering over whether the species was natural or invasive, and whether the museum had released it or not, contributed to a delay that allowed the plant to spread beyond control. The museum continued to deny releasing the plant, although former director Jacques-Yves Cousteau
eventually expressed the belief that it was the only reasonable explanation.
It is reported that as many as half of fish species have disappeared from areas where Caulerpa grows. However, scientific studies have shown that fish diversity and biomass are equal or greater in Caulerpa meadows than in seagrass beds, that Caulerpa had no effect on composition or richness of fish species, and that epiphytic plant richness is greater in Caulerpa than in sea grass.
, that is, vegetatively: the viscous, elastic white fluid inside the stem was found under the microscope to contain only male gamete
s. Rate of growth can be as fast as a centimeter per day. If any small part is severed from the rest of the alga, this small part will regrow into another alga. Anchors of ships and fishing nets can serve as carriers of Caulerpa. Thus this alga has been found to jump from the coast of one port city to the coast of another port city.
The natural strain reproduces sexually and has both male and female individuals. Gametes are expelled from each sex and meet to form a zygote which then goes through two larval stages before becoming an adult.
(U.S.A.), near San Diego
, and also on the coast of New South Wales
, Australia. The California invasion was small enough to be considered controllable: it was covered with tarpaulin
which was held down with sandbags at the edges of the infestation. Then chlorine
was poured in through tubes which fed into certain openings in the tarpaulin: the interior of the tarpaulin filled up with chlorine and killed living organisms inside it, not only the unwanted alga but also fish, invertebrates and other seaweeds. The killing of such other organisms was not desirable but was deemed preferable to letting the weed grow unchecked, which would in the end wield greater havoc to these same creatures.
The appearance off the California coast was most probably caused by an aquarium owner improperly dumping the contents, allowing C. taxifolia to flow through a storm sewer into the lagoon where the invasion was discovered. California has since passed a law forbidding the possession, sale or transport of Caulerpa taxifolia within the state. There is also a federal law under the Noxious Weed Act
forbidding interstate sale and transport of the aquarium strain Caulerpa.
In July 2006, the alga had been declared eradicated from the two Southern California locations (Agua Hedionda Lagoon in Carlsbad and Seagate Lagoon in Huntington).
, it was found off the coast of Florida
, in waters warmer than those in the Mediterranean. This slug is believed to feed exclusively on C. taxifolia, by sticking its proboscis
into the stem and sucking out the white viscous liquid inside the stem: this causes the alga to become limp, discolored, and dead. As the slug does so, it absorbs the alga's poison. The slug has an enzyme
which neutralizes the noxious effect of the poison, and at the same time the poison protects the slug from being eaten by fish. This slug cannot survive in the cooler waters of the Mediterranean, however, and so is unable to check the growth of the killer weed.
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
, an alga of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Caulerpa
Caulerpa
Caulerpa is a genus of seaweeds in the family Caulerpaceae . They are unusual because they consist of only one cell with many nuclei, making them among the biggest single cells in the world...
. Native to the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, it has been widely used ornamentally in aquariums. The alga has a stem which spreads horizontally just above the seafloor, and from this stem grow vertical fern-like pinnae, whose blades are flat like yew
Taxus
Taxus is a genus of yews, small coniferous trees or shrubs in the yew family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of 1-40 m, with trunk diameters of up to 4 m...
, hence the species name "taxifolia" (the genus of yew is "Taxus
Taxus
Taxus is a genus of yews, small coniferous trees or shrubs in the yew family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of 1-40 m, with trunk diameters of up to 4 m...
"). The alga produces a large amount of a single chemical that is toxic to fish and other would-be predators. This is in contrast to other plants which produce a variety of toxins, but in reduced amounts.
It is one of two algae on the list of the world's 100 worst invasive species compiled by the IUCN Invasive Species Specialist Group.
Invasive species
A specific strain of this alga was found to thrive in cold aquarium environments by the staff at the Wilhelma Zoo in Stuttgart, Germany in 1980. Selective breeding under exposure to chemicals and ultra-violet light made the Caulerpa even hardier, and when it eventually found its way into the Mediterranean, it created widespread concern as it threatened to alter the entire ecosystem by crowding out native seaweed while being inedible to animals.It is thought that the seaweed was accidentally released into coastal waters of the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
just below the Oceanographic Museum of Monaco in 1984. Ten years later, Caulerpa had grown to cover 7400 acres (29.9 km²), preventing native plants from growing and leading to the nickname "Killer Algae". Caulerpa overgrows the seabed and disrupts the food cycle dependent on the native plant life. The plant began to spread between ports along the Mediterranean coast. C. taxifolia has been discovered off the coasts of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, though none of these encroachments have been anywhere near the scale of what is happening in the Mediterranean.
For several years, the origin of the species was unclear. Marine biologist
Marine biology
Marine biology is the scientific study of organisms in the ocean or other marine or brackish bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather...
Alexandre Meinesz first discovered the plant in the 1980s, and requested the help of the Monaco Oceanographic Museum, which sat right next to the first known C. taxifolia patch. However, the director of the museum argued that this invasion probably happened naturally, the result of ocean current
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
s carrying a tropical
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
species into the area. Bickering over whether the species was natural or invasive, and whether the museum had released it or not, contributed to a delay that allowed the plant to spread beyond control. The museum continued to deny releasing the plant, although former director Jacques-Yves Cousteau
Jacques-Yves Cousteau
Jacques-Yves Cousteau was a French naval officer, explorer, ecologist, filmmaker, innovator, scientist, photographer, author and researcher who studied the sea and all forms of life in water...
eventually expressed the belief that it was the only reasonable explanation.
It is reported that as many as half of fish species have disappeared from areas where Caulerpa grows. However, scientific studies have shown that fish diversity and biomass are equal or greater in Caulerpa meadows than in seagrass beds, that Caulerpa had no effect on composition or richness of fish species, and that epiphytic plant richness is greater in Caulerpa than in sea grass.
Reproduction mechanism
The aquarium strain reproduces asexuallyAsexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
, that is, vegetatively: the viscous, elastic white fluid inside the stem was found under the microscope to contain only male gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s. Rate of growth can be as fast as a centimeter per day. If any small part is severed from the rest of the alga, this small part will regrow into another alga. Anchors of ships and fishing nets can serve as carriers of Caulerpa. Thus this alga has been found to jump from the coast of one port city to the coast of another port city.
The natural strain reproduces sexually and has both male and female individuals. Gametes are expelled from each sex and meet to form a zygote which then goes through two larval stages before becoming an adult.
Other infestations
In 2000, the strain was found on the coast of CaliforniaCalifornia
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
(U.S.A.), near San Diego
San Diego, California
San Diego is the eighth-largest city in the United States and second-largest city in California. The city is located on the coast of the Pacific Ocean in Southern California, immediately adjacent to the Mexican border. The birthplace of California, San Diego is known for its mild year-round...
, and also on the coast of New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
, Australia. The California invasion was small enough to be considered controllable: it was covered with tarpaulin
Tarpaulin
A tarpaulin, colloquially tarp, is a large sheet of strong, flexible, water-resistant or waterproof material, often cloth such as canvas or polyester coated with urethane, or made of plastics such as polyethylene. In some places such as Australia, and in military slang, a tarp may be known as a...
which was held down with sandbags at the edges of the infestation. Then chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
was poured in through tubes which fed into certain openings in the tarpaulin: the interior of the tarpaulin filled up with chlorine and killed living organisms inside it, not only the unwanted alga but also fish, invertebrates and other seaweeds. The killing of such other organisms was not desirable but was deemed preferable to letting the weed grow unchecked, which would in the end wield greater havoc to these same creatures.
The appearance off the California coast was most probably caused by an aquarium owner improperly dumping the contents, allowing C. taxifolia to flow through a storm sewer into the lagoon where the invasion was discovered. California has since passed a law forbidding the possession, sale or transport of Caulerpa taxifolia within the state. There is also a federal law under the Noxious Weed Act
Federal Noxious Weed Act of 1974
The Federal Noxious Weed Act of 1974 established a federal program to control the spread of noxious weeds. The United States Secretary of Agriculture was given the authority to declare plants "Noxious Weeds", and limit the interstate spread of such plants without a permit...
forbidding interstate sale and transport of the aquarium strain Caulerpa.
In July 2006, the alga had been declared eradicated from the two Southern California locations (Agua Hedionda Lagoon in Carlsbad and Seagate Lagoon in Huntington).
Possible natural control method
Researchers at the University of Nice in France have been studying a tiny aquatic slug which is known to be a natural predator of C. taxifolia. Called Elysia subornataElysia subornata
Elysia subornata is a species of small sea slug, a marine opisthobranch gastropod mollusk in the family Placobranchidae.This sea slug resembles a nudibranch, but it is not closely related to that order of gastropods, instead it is a sacoglossan....
, it was found off the coast of Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
, in waters warmer than those in the Mediterranean. This slug is believed to feed exclusively on C. taxifolia, by sticking its proboscis
Proboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...
into the stem and sucking out the white viscous liquid inside the stem: this causes the alga to become limp, discolored, and dead. As the slug does so, it absorbs the alga's poison. The slug has an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
which neutralizes the noxious effect of the poison, and at the same time the poison protects the slug from being eaten by fish. This slug cannot survive in the cooler waters of the Mediterranean, however, and so is unable to check the growth of the killer weed.
External links
- In-depth article on invasions of Caulerpa taxifolia, source as escaped aquarium plant, etc.
- Caulerpa Taxifolia fact sheet
- An excerpt from Killer Algae by Alexandre Meinesz
- Caulerpa taxifolia at the Center for Invasive Species Research
- "Deep Sea Invasion" Nova (TV series)NOVA (TV series)Nova is a popular science television series from the U.S. produced by WGBH Boston. It can be seen on the Public Broadcasting Service in the United States, and in more than 100 other countries...
broadcast April 1, 2003 - Species Profile- Caulerpa, Mediterranean Clone (Caulerpa taxifolia), National Invasive Species Information Center, United States National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for Caulerpa, Mediterranean Clone.