Feathered caulerpa

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 species of algae listed in 100 of the World's Worst Invasive Alien Species compiled by the IUCN Invasive Species Specialist Group.^[5]

C. taxifolia is light green^[3] with stolons (stems) on the sea floor, from which sparsely-branched upright fronds of approximately 20–60 cm (8–24 in) in height arise.^[6] Algae in the genus Caulerpa synthesize a mixture of toxins^[7] termed , believed to impart a peppery taste to the plants.^[8] The effects of the specific toxin synthesized by C. taxifolia, , have been studied,^[9][10] with extracts from C. taxifolia being found to negatively affect P-glycoprotein-ATPase in the sea sponge G. cydonium.^[11]

Like all members of the genus Caulerpa, C. taxifolia consists of a single cell with many nuclei. The algae has been identified as the largest known single-celled organism.^[12] Wild-type C. taxifolia is monoecious.^[13]

Caulerpa species are commonly used in aquaria for their aesthetic qualities and ability to control the growth of undesired species.^[14] C. taxifolia has been cultivated for use in aquaria in western Europe since the early 1970s.^[15] A clone of the alga that was resistant to cold was observed in the tropical aquarium at the Wilhelma Zoo in Stuttgart^[16] and further bred by exposure to chemicals and ultraviolet light.^[17] The zoo distributed the strain to other aquaria, including the Oceanographic Museum of Monaco.^[16]

The aquarium strain is morphologically identical to native populations of the species.^[3] However, a 2008 study found that a population of the aquarium strain near Caloundra, Australia exhibited markedly reduced sexual reproduction, with only male plants present during some reproductive episodes.^[13] The aquarium strain can survive out of water for up to 10 days in moist conditions, with 1 cm fragments capable of producing viable plants.^[18]

Outside its native range, C. taxifolia is listed as an invasive species.^[19][20] 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] The species is able to thrive in heavily polluted waters,^[21] possibly contributing to its spread in the Mediterranean.^[22]

The presence of C. taxifolia in the Mediterranean was first reported in 1984^[23] in an area adjacent to the Oceanographic Museum of Monaco.^[24] Alexandre Meinesz, a marine biologist, attempted to alert Moroccan and French authorities to the spread of the strain in 1989,^[16] but the governments failed to respond to his concerns.^[25] The occurrence of the strain is generally believed to be due to an accidental release by the museum,^[3][26] but Monaco rejected the attribution and instead claimed that the observed algae was a mutant strain of C. mexicana.^[25] By 1999, scientists agreed that it was no longer possible to eliminate the presence of C. taxifolia in the Mediterranean.^[25]

A study published in 2002 found that beds of Posidonia oceanica in the Bay of Menton were not negatively affected eight years after colonization by C. taxifolia.^[27] Other published studies have shown that fish diversity and biomass are equal or greater in Caulerpa meadows than in seagrass beds^[28] and that Caulerpa had no effect on composition or richness of fish species.^[29]

Studies in 1998^[15] and 2001^[23] found that the strain observed in the Mediterranean was genetically identical to aquarium strains, with similarities to an additional population in Australia.

A 2007 study found that a native bivalve mollusc species was negatively affected by the presence of C. taxifolia, but that the effect was not necessarily different from that of native seagrass species.^[30] A 2010 study indicated that the effect of detritus from C. taxifolia negatively impacted abundance and species richness.^[31]

C. taxifolia was found in waters near San Diego, California, in 2000,^[32] where chlorine bleach was used in efforts to eradicate the strain.^[33] The strain was declared eradicated from Agua Hedionda Lagoon in 2006.^[34] California passed a law in 2001 forbidding the possession, sale, transport, or release of Caulerpa taxifolia within the state.^[35] The Mediterranean clone of C. taxifolia was listed as a noxious weed in 1999^[36] 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.^[24][37]

C. taxifolia may become entangled in fishing gear and boat propellers.^[4]

C. taxifolia may be controlled via mechanical removal, poisoning with chlorine, or application of salt.^[6] Researchers at the University of Nice investigated possible use of a species of sea slug, Elysia subornata, as a possible natural control method, but found that it was not suitable for use in the Mediterranean due to cold winter water temperatures and insufficient population density.^[38]

• 
  C. taxifolia on display at the National Museum of Nature and Science in Tokyo, Japan
• 
  A field of C. taxifolia amongst seagrass
• 
  A Pacific cleaner shrimp (Lysmata amboinensis) on top of a C. taxifolia specimen within a marine aquarium

• Largest organisms

• Peplow, Mark (23 March 2005). "Algae create glue to repair cell damage". Nature: news050321–11. doi:10.1038/news050321-11.
• LaMonica, Martin (20 May 2005). "Start-up drills for oil in algae". CNET.
• Theodoropoulos, David. 2003. Invasion Biology: Critique of a Pseudoscience. pages 42,159. Avvar Books, Blythe, CA. 237 p. ISBN 0-9708504-1-7

• Attack of the killer algae - Eric Noel Muñoz on YouTube
• Killer Algae, 2001 BBC Documentary
• In-depth article on invasions of Caulerpa taxifolia, source as escaped aquarium plant, etc.
• Caulerpa Taxifolia fact sheet Archived 2022-10-08 at the Wayback Machine
• An excerpt from Killer Algae by Alexandre Meinesz
• Caulerpa taxifolia at the Center for Invasive Species Research
• "Deep Sea Invasion" Nova (TV series) broadcast April 1, 2003
• Species Profile- Caulerpa, Mediterranean Clone (Caulerpa taxifolia), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Caulerpa, Mediterranean Clone.