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Killer Alga

Caulerpa taxifolia

Brief Summary

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“Caulerpa taxifolia is an invasive marine alga that is widely used as a decorative plant in aquaria. A cold-tolerant strain was inadvertently introduced into the Mediterranean Sea in wastewater from the Oceanographic Museum at Monaco, where it has now spread over more than 13,000 hectares of seabed. Caulerpa taxifolia forms dense monocultures that prevent the establishment of native seaweeds and excludes almost all marine life, affecting the livelihoods of local fishermen.”

(NIMPIS 2011, Caulerpa taxifolia general information, National Introduced Marine Pest Information System, viewed 29 January 2011 <http://www.marinepests.gov.au/nimpis>)

See also: Southern California Caulerpa Action Team

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Distribution

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Native circum-tropical distribution: Africa, Australia, Bermuda, China, Fiji, India, Japan, Maldives, New Caledonia, Hawaii (USA)

Non-native range: Australia, Croatia, France, Germany, Italy, Monaco, New Zealand, Spain, Tunisia, California (USA)

(Global Invasive Species Database – Caulerpa taxifolia viewed 29 January 2011)

First observed in Mediterranean in 1984 in Monaco from which it spread rapidly (Bourdouresque et al., 1995). Found in Southern California 12 June 2000, where rapid-respone eradication and control measures seem to have been fairly effective (Williams & Grosholz, 2002; Anderson, 2005; SCCAT accessed 1 February 2011).

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Habitat

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Substrate: rock, sand, seagrass

Depth: 3 to 35 m, though to 100 m in Mediterranean

(NIMPIS 2011, Caulerpa taxifolia reproduction and habitat, National Introduced Marine Pest Information System, viewed 29 January 2011 <http://www.marinepests.gov.au/nimpis>)

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Legislation

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United States Law: It is illegal to import or transport Caulerpa taxifolia aquarium strain across state lines including internet sale (Federal Noxious Weed Act, 1999; and Federal Plant Protection Act, 2000).

California State Law: It is illegal to possess, transport, transfer, release alive, import, or sell Caulerpa taxifolia, Caulerpa sertularioides, Caulerpa mexicana, Caulerpa ashmeadii, Caulerpa scalpelliformis, Caulerpa racemosa (and all varieties of C. racemosa), Caulerpa cupressoides, Caulerpa verticillata, Caulerpa floridana (California Fish and Game Code 2300).

City of San Diego Law: Bans the possession, sale, and transport of all Caulerpa species within city limits (City of San Diego Ordinance 18967).

(California Sea Grant - Caulerpa species identification key - accessed 1 February 2011)

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Lookalikes

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Caulerpa taxifolia is similar in appearance to C. scalpelliformis, C. mexicana, C. sertularioides, and C. ashmeadii -- all also illegal in California (USA) (California Sea Grant - Caulerpa species identification key - "feather").

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Morphology

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“Caulerpa taxifolia is a light green macroalga with upright leaf-like fronds arising from creeping stolons. The fronds are flattened laterally and the small side branchlets are constricted at the base (where they attach to the midrib of each frond), are opposite in their attachment to the midrib (as opposed to alternating) and curve upwards and narrow towards the tip. The invasive aquarium clone is morphologically identical to native populations of the species. Frond diameter is 6-8mm and frond length is usually 3-15cm in the shallows, 40-60cm in deeper situations but can grow up to 2.8m in height.”

(NIMPIS 2011, Caulerpa taxifolia general information, National Introduced Marine Pest Information System, viewed 29 January 2011 <http://www.marinepests.gov.au/nimpis>.)

See also: California Sea Grant - Caulerpa species identification key - "feather"

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Reproduction

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In its native tropics, it reproduces sexually and vegetatively. In its invasive range in the Mediterranean, all reproduction is believed to be via thallis fragmentation. Though male gametes are produced (synchronously) there are no female gametes, suggesting this population is an all-male clone (Žuljević & Antolić, 2000).

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Risk Statement

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Highly invasive, spreading rapidly and leading to reduced numbers and diversity of other algae, invertebrates, and fish (Bourdouresque et al., 1995; Balata et al., 2004).

Vectors for introduction: ornamental aquaria (public and private), fisheries and aquaculture, natural dispersal from introduced populations, vessels (NIMPIS 2011, Caulerpa taxifolia general information, National Introduced Marine Pest Information System, viewed 29 January 2011 <http://www.marinepests.gov.au/nimpis>).

See also: Southern California Caulerpa Action Team

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Trophic Strategy

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Photosynthesis. Capable of enhancing N2 fixation, giving it another competitive advantage in nutrient-poor waters.

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Uses

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Popular aquarium plant in both private and public aquaria.

Caulerpenyne, the major metabolite present in Caulerpa taxifolia, may have anti-tumor activity (Fischel et al., 1995).

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Caulerpa taxifolia

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Caulerpa taxifolia is a species of seaweed, an alga of the genus Caulerpa native to the Indian Ocean. It is widely used ornamentally in aquariums, because it is considered attractive and neat in arrangement, and is easy to establish and care for. The alga has a stem (rhizome) which spreads horizontally just above the seafloor. From this stem grow vertical fern-like pinnae, whose blades are flat like those of the yew (Taxus), hence the species name taxifolia.

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.

Description

"
Two illustrations (Fig 1 . 4-5) of C. taxifolia displaying its "leaf" and rhizome structures (Fig 1 . 1-3 are illustrations of C. sertularioides)

Unlike most aquarium macro algae, C. taxifolia (Killer Algae) has the appearance of a vascular plant with "leaves" arranged neatly up stalks, like a fern. Behind this appearance, the plant is a typical macro alga, without the vascular system to transmit nutrients and cells that plants originally evolved on land have. Caulerpa taxifolia is a single celled organism, but this is often overlooked because of its complexity and size.

Caulerpa taxifolia has been described as storing in its "leaves" a single chemical, 'caulerpicin', that is noxious to fish and other would-be predators, though not toxic to the water around it. This is in contrast to plants which produce a variety of toxins, but in reduced amounts. On the other hand, studies have found that there is reduced pollution and toxicity in waters where it grows invasively, as around port cities in the Mediterranean. Original concerns about it decreasing biodiversity of fauna have also been allayed, as species counts have shown this remains about the same.

Introduced species

In 1980, the staff at the Wilhelma Zoo in Stuttgart, Germany found that a specific strain of this alga thrived in cold aquarium environments. Selective breeding under exposure to both chemicals and ultra-violet light produced even hardier Caulerpa strains.[2] When it eventually found its way into the Mediterranean, widespread concern developed that the algae 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 just below Jacques Cousteau's Oceanographic Museum of Monaco in 1984. Ten years later, the claim was made that Caulerpa had grown to cover 3,000 hectares (7,400 acres),[3] and was preventing native plants from growing. This concern earned the algae the dubious nickname "Killer Algae" after the title of a book written on the subject.[4] Its author, Marine biologist Alexandre Meinesz first discovered the alga in the 1980s, and requested the help of the Monaco Oceanographic Museum, which sat right next to the first known C. taxifolia patch. The director of the museum argued that this invasion probably happened naturally, the result of ocean currents carrying a tropical species into the area. The parties bickered publicly for years over whether the species was natural or invasive, and whether the museum had released it or not, at the expense of sound scientific research on the species and its ecological significance.

Beds of the algae typically inhabit polluted, nutrient-rich areas such as sewage outfalls,[5] explaining its spread among port cities in the Mediterranean Sea. This actually reduces the pollution in those areas, as the caulerpa consumes it: In an eight-year study of Caulerpa beds in the French Bay of Menton by the European Oceanographic Observatory of Monaco (based within the Museum of Monaco[6]), it was found that the alga reduced pollution and aided in the recovery of native Posidonia seagrass.[7]

Despite claims that as many as half of fish species have disappeared from areas where Caulerpa grows, scientific studies have shown that fish diversity and biomass are equal or greater in Caulerpa meadows than in seagrass beds,[8] that Caulerpa had no effect on composition or richness of fish species,[9] and that species richness and epiphytic plant diversity is greater in Caulerpa than in pure sea grass. Thus, in contrast to widely publicized reports to the contrary, the species appears to have many beneficial ecological effects on aquatic communities in the Mediterranean Sea.

Aquarist Jean Jaubert, director of the aforementioned Oceanographic Museum of Monaco, has said that the affected areas in the nearby Bay of Menton have been exaggerated 100-fold.

Reproduction mechanism

The aquarium strain reproduces asexually, that is, vegetatively: the viscous, elastic white fluid inside the stem was found under the microscope to contain only male gametes. 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 for 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 has both male and female individuals and additionally reproduces sexually. Gametes are expelled from each sex and meet to form a zygote which then goes through two larval stages before becoming an adult.

Other introductions

In 2000, the strain was found on the coast of California (U.S.), near San Diego, and also on the coast of New South Wales, Australia. The California colonization 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 algae grow unchecked.

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 Beach).

Possible natural control method

Researchers at the University of Nice in France have been studying a tiny aquatic slug which is a natural predator of C. taxifolia.[10] Called Elysia subornata, 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. However, this slug cannot survive in the cooler waters of the Mediterranean and, therefore, is unable to control the invasive alga there.

Gallery

References

  1. ^ Guiry, M.D.; Guiry, G.M. (2007). "Genus: Caulerpa taxonomy browser". AlgaeBase version 4.2 World-wide electronic publication, National University of Ireland, Galway. Retrieved 2007-09-23.
  2. ^ Pierre Madl; Maricela Yip (2004). "Literature Review of Caulerpa taxifolia". BUFUS-Info. 19 (31). Retrieved 2007-06-10.
  3. ^ Bright, C. 1998. Life out of bounds: Bio-invasion in a borderless world. W. W. Norton & Company, New York.
  4. ^ Meinesz, A. 1999. Killer algae. University of Chicago Press, Chicago.
  5. ^ Frakes, T.A. 2001. Killer algae: Ecological disaster or media hysteria? Submitted during the hearing in California concerning the proposed bill # 1334 available at http://www.aquarium-design.com/reef/caulerpa.html
  6. ^ Meinesz, p. 206
  7. ^ Jaubert, J.M., J.R.M. Chisholm, G. Passeron-Seitre, D. Ducrot, H.T. Ripley, and L. Roy. 1999. No deleterious alterations in Posidonia beds in the Bay of Menton (France) eight years after Caulerpa taxifolia colonization. Journal of Phycology 25:1113-1119.
  8. ^ Relini, G., M Relini, and G. Torchia. (1998) Fish biodiversity in a Caulerpa taxifolia meadow in the Ligurian Sea. Italian Journal of Zoology 65 Supplement:465-470.
  9. ^ Francour, P., M. Harmelin-Vivien, J. G. Harmelin, and J. Duclerc. 1995. Impact of Caulerpa taxifolia colonization on the littoral ichthyofauna of north-western Mediterranean sea. Hydrobiologia 300-301:345-353.
  10. ^ Thibaut, T. 2001. "Elysia subornata a potential control agent of the alga Caulerpa taxifolia in the Mediterranean Sea" Archived 2005-10-25 at the Wayback Machine, Journal of the Marine Biological Association of the United Kingdom

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Caulerpa taxifolia: Brief Summary

provided by wikipedia EN

Caulerpa taxifolia is a species of seaweed, an alga of the genus Caulerpa native to the Indian Ocean. It is widely used ornamentally in aquariums, because it is considered attractive and neat in arrangement, and is easy to establish and care for. The alga has a stem (rhizome) which spreads horizontally just above the seafloor. From this stem grow vertical fern-like pinnae, whose blades are flat like those of the yew (Taxus), hence the species name taxifolia.

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.

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Wikipedia authors and editors
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