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Caulerpa taxifolia

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Caulerpa taxifolia
Scientific classification Edit this classification
Clade: Viridiplantae
Division: Chlorophyta
Class: UTC clade
Order: Bryopsidales
Family: Caulerpaceae
Genus: Caulerpa
Species:
C. taxifolia
Binomial name
Caulerpa taxifolia
(M.Vahl) C.Agardh, 1817[1]

Caulerpa taxifolia is a species of green seaweed, an alga of the genus Caulerpa native to tropical waters of the Pacific Ocean, Indian Ocean, and Caribbean Sea.[2] The species name taxifolia arises from the resemblance of its leaf-like fronds[3] to those of the yew (Taxus). [citation needed]

A strain of the species bred for use in aquariums has established non-native populations in waters of the Mediterranean Sea, the United States, and Australia.[4] It is one of two algae listed as one of the 100 worst invasive species compiled by the IUCN Invasive Species Specialist Group.[5]

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 the biggest unicellular organism.[6]

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.[citation needed] 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.[citation needed] Original concerns about it decreasing biodiversity of fauna have also been allayed, as species counts have shown this remains about the same.[citation needed]

Status as invasive species

Outside its native range, C. taxifolia is listed as an invasive species.[7][8] 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.[5]

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.[9] 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.[citation needed]

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),[10] and was preventing native plants from growing.[citation needed] This concern earned the algae the nickname "Killer Algae" after the title of a book written on the subject.[11] Its author, Marine biologist Alexandre Meinesz, first discovered the alga in the 1980s, and requested the help of the Oceanographic Museum of Monaco, which sat right next to the first known C. taxifolia patch.[citation needed] The director of the museum argued that this invasion probably happened naturally, the result of ocean currents carrying a tropical species into the area.[citation needed] The parties bickered publicly for years over whether the species was natural or invasive, and whether the museum had released it or not.[citation needed]

Beds of the algae often successully inhabit polluted, nutrient-rich areas such as sewage outfalls,[12] 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[13]), it was found that the alga reduced pollution and aided in the recovery of native Posidonia seagrass.[14]

Despite claims that as many as half of fish species have disappeared from areas where Caulerpa grows,[citation needed] scientific studies have shown that fish diversity and biomass are equal or greater in Caulerpa meadows than in seagrass beds,[15] that Caulerpa had no effect on composition or richness of fish species,[16] and that species richness and epiphytic plant diversity is greater in Caulerpa than in pure sea grass.[citation needed]

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.[citation needed]

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.[citation needed] Rate of growth can be as fast as a centimeter per day.[citation needed] If any small part is severed from the rest of the alga, this small part will regrow into another alga.[citation needed] Anchors of ships and fishing nets can serve as carriers for Caulerpa.[citation needed] Thus, this alga has been found to jump from the coast of one port city to the coast of another port city.[citation needed] 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.[citation needed]

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.[citation needed] The killing of such other organisms was not desirable but was deemed preferable to letting the algae grow unchecked.[citation needed]

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.[citation needed] California passed a law in 2001 forbidding the possession, sale, transport, or release of Caulerpa taxifolia within the state.[17][18] The Mediterranean clone of Caulerpa taxifola was listed as a noxious weed in 1999[19] by the Animal and Plant Health Inspection Service, prohibiting interstate sale and transport of the strain without a permit under the Noxious Weed Act and Plant Protection Act.[17][20]

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).[citation needed]

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.[21] 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.[citation needed]

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. ^ https://dnr.wi.gov/topic/Invasives/documents/classification/LR_Caulerpa_taxifolia.pdf
  3. ^ Invasive Species Specialist Group http://www.iucngisd.org/gisd/species.php?sc=115. Retrieved 2021-05-23. {{cite web}}: Missing or empty |title= (help)
  4. ^ "Aquarium Aulerpa". Marine Biosecurity Porthole. Retrieved 2021-05-23.
  5. ^ a b "100 of the World's Worst Invasive Alien Species". Global Invasive Species Database (International Union for Conservation of Nature (IUCN)). Retrieved Jan 24, 2021.{{cite web}}: CS1 maint: url-status (link)
  6. ^ "Structure of world's largest single cell is reflected at the molecular level". ScienceDaily. Retrieved 2021-02-21.
  7. ^ "Caulerpa taxifolia". Invasive Species Compendium (CABI International). Retrieved Jan 24, 2021.{{cite web}}: CS1 maint: url-status (link)
  8. ^ "Caulerpa taxifolia". Center for Aquatic and Invasive Plants (University of Florida). Retrieved Jan 24, 2021.{{cite web}}: CS1 maint: url-status (link)
  9. ^ Pierre Madl; Maricela Yip (2004). "Literature Review of Caulerpa taxifolia". BUFUS-Info. 19 (31). Retrieved 2007-06-10.
  10. ^ Bright, C. 1998. Life out of bounds: Bio-invasion in a borderless world. W. W. Norton & Company, New York.
  11. ^ Meinesz, A. 1999. Killer algae. University of Chicago Press, Chicago.
  12. ^ 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
  13. ^ Meinesz, p. 206
  14. ^ 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.
  15. ^ 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.
  16. ^ 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.
  17. ^ a b "Aquatic Invasive Species on the West Coast". NOAA Fisheries. Retrieved 2021-05-23.
  18. ^ "Assembly Bill No. 1334, Chapter 338". California Legislative Information. Retrieved 2021-05-23.
  19. ^ "Noxious Weeds; Notice of Availability of Petitions To Regulate Caulerpa". Federal Register. Retrieved 2021-05-23.
  20. ^ "Noxious Weed Regulations" (PDF). govinfo.gov. Retrieved 2021-05-23.
  21. ^ 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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