Caulerpa taxifolia

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Caulerpa taxifolia
CaulerpaTaxifolia.jpg

Caulerpa taxifolia

Systematics
without rank: Chlorophyta
Class : Bryopsidophyceae
Order : Caulerpales
Family : Caulerpaceae
Genre : Caulerpa
Type : Caulerpa taxifolia
Scientific name
Caulerpa taxifolia
( Vahl ) Agardh , 1817

Caulerpa taxifolia is a species of green algae from the Chlorophyta . It was best known for the occurrences introduced into the Mediterranean. It reproduces there clonally, i.e. asexually, and is now widespread. It overgrows the local seagrass meadows and thereby destroys the animals' livelihoods. That is why it was given the name "killer algae". Because the alga is poisonous, it has no natural enemies in the Mediterranean. Since about 2000 the population of the species in the Mediterranean Sea has been declining for unknown reasons.

Later, first recorded in 2006 on the Turkish Mediterranean coast, another strain of the species appeared in the Mediterranean, which is not identical to the invasive clan from the aquariums. It is taxonomically referred to as Caulerpa taxifolia (Vahl) C. Agardh var. Distichophylla (Sonder) Verlaque, Huisman and Procaccini.

With Caulerpa racemosa (the invasive clan later redefined as Caulerpa cylindracea ), another species of the same genus was introduced into the Mediterranean, where it causes similar problems, which are now even greater. Other introduced species of the genus are less conspicuous.

Construction and shape

The thallus of Caulerpa taxifolia is, as is typical of the genus, divided into green axes that creep on the bottom of the water ( stolons , about 0.8 to 2.5 mm wide in the species), which are anchored on the substrate by outgoing colorless, branched filaments ( called rhizoids because of their similarity to roots ). From the stolons upright growing, leaf-like side branches branch off at regular intervals, these are called phylloids because of their shape similar to a leaf or because of their main importance for photosynthesis , they are called assimilators . The scientific name of the species taxifolia is derived from the shape of these phylloids: Taxus = yew and folia = leaves. The entire thallus is not chambered by partitions and not divided into individual cells; the entire cytoplasm forms an undivided association called syncytium with numerous cell nuclei. There are also numerous small chloroplasts and also chlorophyll-free storage organelles called amyloplasts in the cytoplasm . The interior (lumen) of the phylloids is stiffened by inwardly growing extensions of the cell wall, which cross it from wall to wall like a bridge, these are called trabeculae .

Caulerpa taxifolia can be distinguished from other species of the genus morphologically by the following characteristics: Assimilators pale green, leaf-shaped, not vesicular. These consist of a normally unbranched central axis ( rachis ) from which two lines of opposite side rungs branch off. These side branches are longer than the diameter of the rachis, they are clearly flattened (not petite-round). They usually reach a length of about 5 to 9 millimeters in calm water, but there are thalli in areas with agitated water, the phylloids of which have only short, 1 to 2 millimeter long side branches (sometimes also taxonomically differentiated as var. Falcifolia or var . distichophylla ). The side branches are flat, leaf-like, slightly constricted at the base, straight or (usually) noticeably curved upwards, with a sharp tip. A gap can be formed between the side branches, or they more or less directly abut one another.

The species of the genus Caulerpa are morphologically quite variable depending on the environmental conditions, which means that numerous forms have been described and it is difficult to differentiate between the species. Stolons of the species usually reach a length of about eight inches. Occasionally, however, under particularly favorable conditions, giant forms occur with thalli that are 2.5 meters long. These are among the largest single cells known to date.

Caulerpa species differ from one another in the degree of ploidy, even within the same species. Examined thalli of Caulerpa taxifolia turned out to be diploid .

It is natural to ask how the flow of genetic information controls the metabolism in the syncytium. A general pattern was found that extends from the base to the front vertex, with transcription and subsequent translation being localized to specific cell regions.

Life cycle

Caulerpa taxifolia normally spreads asexually vegetatively , through fragmentation of the thalli. Torn off assimilators are carried away by currents and can regenerate into whole plants when they come into contact with the ground again. If a part of such an alga is pulled out with a ship's anchor and gets into another bay, a complete, spreading alga grows from this piece again. Caulerpa taxifolia can also survive a certain amount of dehydration without major damage. Anchors, in particular, tear parts of the algae from the shallow seabed and carry them to other sea sections (so-called agochory ). In fact, the first occurrences of C. taxifolia were only found in the vicinity of ports.

Sexual reproduction has also been proven in the natural area of ​​origin of the species. During sexual reproduction, an entire thallus turns to the production of gametes , the entire cytoplasm is converted into gametes. Only the empty, then pure white colored cell wall of the old thallus remains. Only a certain proportion of the thalli, around five to twenty percent, switch synchronously to sexual reproduction. Within the species next to each other individuals and populations come with-female-male and those on the same thallus adjacent male and female gametes produce ( monoecism or Einhäusigkeit called) before. Neither what triggers sexual reproduction as a whole nor what then determines the sex of the gametes is known; environmental stimuli that have not yet been identified are assumed.

When gametogenesis begins , the thalli first change their color. The cytoplasm withdraws from the stolons, within the phylloids a network-like pattern is formed. New tubes a few millimeters long are formed on the surface of the rachis, from which the gametes are ultimately released. The finished gametes are round (pear-shaped) and have the same shape between the sexes, the female a little larger (5 to 8 compared to 4 to 5 micrometers). At one pole there are two flagella of the same shape . Every gamete has a nucleus and a chloroplast. Only the female gametes have an eye spot. The males are faster and more active swimmers. When two gametes of different sexes meet, they sometimes fuse to form a diploid zygote . Often there is no merging, incompatible strains may exist.

As far as is known, the Caulerpa taxifolia populations introduced into the Mediterranean Sea never reproduce sexually. However, the formation of gametes has been observed in one population in the Adriatic Sea. Here numerous thalli released numerous gametes at water temperatures above 25 ° C, synchronized by the exposure. Since all of them were male, fertilization did not occur.

distribution

Caulerpa taxifolia is found in warm, tropical seas almost worldwide, provided that the water temperature in winter exceeds 15 ° C. Occurrences are given for the eastern Pacific Ocean and the Indian Ocean, south to the tropical north coast of Australia (including Lord Howe Island ), north to south China and on the coasts of Iran, on the coast of numerous islands of Oceania , on the east and west coast of Africa, in the west Atlantic from Brazil in the south through the Caribbean to Florida in the north.

Introduced by humans, the species occurs in numerous places along the temperate south coast of Australia, except in the Mediterranean. An introduced occurrence in Japan died out by itself due to the low water temperatures. An imported occurrence on the North American Pacific coast in California was immediately fought hard and is now considered to be eradicated again.

Origin of occurrences in the Mediterranean

Researchers at the University of Geneva came to the conclusion that this type of algae is a neophyte that presumably comes from the marine area east of Australia .

Genetic studies seem to confirm that all individuals of this species in the Mediterranean are descended from an alga.

This one alga originally comes from the botanical-zoological garden in Stuttgart , the Wilhelma . In its aquarium department, Caulerpa taxifolia is very popular as aquarium algae , as it is not or only very slowly overgrown by red algae due to toxic excretions . This reduces the cleaning effort enormously. Because of these properties, Caulerpa taxifolia was passed on to the aquarium of the Oceanographic Institute of Monaco . One hypothesis is that it ended up in the Mediterranean with the sewage from the aquarium. There are also rumors that employees have deliberately exposed the algae. It is undisputed that the alga first appeared off Monaco in the Mediterranean. From there it was spread with ship anchors to Italy, along the Cote d'Azur and to the Balearic Islands . The invasion of the Mediterranean could not be stopped.

Recent studies have clearly confirmed that the tribe introduced into the Mediterranean originally came from the Indo-Pacific around Australia.

Combat

When a smaller occurrence of C. taxifolia was also found on the coast of California , this was combated by putting a tarpaulin over the algae meadow. The alga was then killed with chlorine . This method also exterminates harmless animals and plants; the costs are also far too high to be used across the whole of the Mediterranean.

One studies a species of snail, Elysia subornata , which feeds on C. taxifolia . It uses special enzymes to neutralize the poison of the algae.

The only native to the Mediterranean fish species Caulerpa calcareous grasslands graze, are Salema porgy ( Sarpa salpa ) and boops boops ( Boops boops ) from the family of sea bream. They feed mainly on the upright stolons, with a maximum in autumn, which results in a bushier growth of the algae. This did not trigger a significant decline in algae.

In laboratory tests, Caulerpa extracts and dissolved Caulerpin in the cell of a marine sponge apoptosis out.

"Killer alga"

The unobjective name "killer algae" does not refer to active killing, but describes the gradual overgrowth of the original marine flora. Much of the marine ecosystem in the Mediterranean is based on the primary producer of seaweed . It produces the nutrients, provides a habitat for many algae and animal species, which in turn form the basis of food for fish etc. a. Form marine animals. C. taxifolia overgrows the seaweed and deprives it of sunlight and nutrients, so that it dies. Then (almost) all other algae and animals also disappear. However, there are different assessments of the size of the problem. Some researchers are of the opinion that Caulerpa would, above all, opportunistically nest in gaps in the seagrass meadows that have arisen for other reasons and that it is not even able to actively displace them.

Decrease after 2000

After the extremely rapid initial spread in the years 1984 to around 2000, the species did not spread as much as was originally forecast. The further expansion initially came to a standstill, later the species disappeared again from a large part of the previously populated areas for reasons that have not yet been understood. So it disappeared completely from the waters off Sicily from around 2004. A sharp decline on the Croatian Adriatic coast from 2000 also set in spontaneously, although intensive control measures had proven completely ineffective in previous years. It is not related to a change in water temperature here.

literature

  • Peter Sitte , Elmar Weiler, Joachim W Kadereit, Andreas Bresinsky, Christian Körner: Textbook of botany for universities. Founded by E. Strasburger. 35th edition. Spectrum Academic Publishing House, Heidelberg 2002. ISBN 3-8274-1010-X
  • CF Boudouresque, A Meinesz, V Gravez: First international workshop on Caulerpa taxifolia. Nice, France, 17-18 January 1994. GIS Posidonie , Marseille, France. 1994: 392 pages.

Individual evidence

  1. ^ A Meinesz, B Hesse: Introduction of the tropical alga Caulerpa taxifolia and its invasion of the northwestern Mediterranean. In: Oceanologica Acta 14, 4, 1991: 415-426.
  2. ↑ Alexander Meinesz: Killer algae. The true tale of a biological invasion. (translated by Daniel Simberloff). University of Chicago Press, Chicago and London, 1997. ISBN 0-226-51922-8 , p. 77.
  3. ↑ Cem Cevik, Mehmet Baki Yokes, Levent Cavas, Levent Itri Erkol, Osman Baris Derici, Marc Verlaque (2006): First report of Caulerpa taxifolia (Bryopsidales, Chlorophyta) on the Levantine coast (Turkey, Eastern Mediterranean). Estuarine, Coastal and Shelf Science 74: 549-556. doi: 10.1016 / j.ecss.2007.05.031
  4. ↑ Judith Klein, Marc Verlaque (2008): The Caulerpa racemosa invasion: A critical review. Marine Pollution Bulletin 56: 205-225. doi: 10.1016 / j.marpolbul.2007.09.043
  5. ↑ Eduard Strasburger et al; Revised by Peter Sitte, Hubert Ziegler, Friedrich Ehrendorfer, Andreas Bresinsky: Textbook of botany for universities. 33rd edition. Gustav Fischer, Stuttgart, Jena, New York 1991; → p. 637f. ISBN 3-437-20447-5 .
  6. ^ A b c Gareth S. Belton, John Huisman, Carlos FD Gurgel: Caulerpaceae. In JD Huisman (editor): Algae of Australia. Marine Benthic Algae of North-western Australia. 1. Green and Brown Algae. CSIRO, Collingwood 2015. ISBN 978 1486304493 .
  7. ↑ Alexander Meinesz: Killer algae. The true tale of a biological invasion. (translated by Daniel Simberloff). University of Chicago Press, Chicago and London, 1997. ISBN 0-226-51922-8 , p. 295.
  8. ↑ Elena Varela-Alvarez, Amelia Gomez Garreta, Jordi Rul Lluch, Noemi Salvador Soler, Ester A. Serrao, Maria Antonia Ribera Siguan (2012): Mediterranean Species of Caulerpa Are Polyploid with Smaller Genomes in the Invasive Ones. PLoS ONE 7 (10): e47728. doi: 10.1371 / journal.pone.0047728
  9. ↑ Aashish Ranjan, Brad T Townsley, Yasunori Ichihashi, Neelima R Sinha, Daniel H Chitwood: An intracellular transcriptomic atlas of the giant coenocyte Caulerpa taxifolia: In: PLOS Genetics 11, 1, 2015: e1004900. PMC 4287348 (free full text)
  10. ↑ Julie A. Phillips (2009): Reproductive ecology of Caulerpa taxifolia (Caulerpaceae, Bryopsidales) in subtropical eastern Australia. European Journal of Phycology 44 (1): 81-88. doi: 10.1080 / 09670260802343640
  11. ↑ Alexander Meinesz: Killer algae. The true tale of a biological invasion. (translated by Daniel Simberloff). University of Chicago Press, Chicago and London, 1997. ISBN 0-226-51922-8 , pp. 298-299.
  12. ↑ Ante Žuljević & Boris Antolić (2000): Synchronous release of male gametes of Caulerpa taxifolia (Caulerpales, Chlorophyta) in the Mediterranean Sea. Phycologia 39 (2): 157-159.
  13. ↑ Wendy Guiry in Guiry, MD & Guiry, GM 2020. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway www.algaebase.org, accessed July 13, 2020.
  14. ↑ Caulerpa taxifolia (M.Vahl) C. Agardh. GBIF Global Biodiversity Information Facility , accessed July 13, 2020.
  15. ↑ Caulerpa: Species Guide at a Glance Aquatic Invasions! A Menace to the West, Species Guide. Oregon Sea Grant, Oregon State University.
  16. ↑ J. Wiedenmann, A. Baumstark, TL Pillen, A. Meinesz W. Vogel (2001): DNA fingerprints of Caulerpa taxifolia provide evidence for the introduction of an aquarium strain into the Mediterranean Sea and its close relationship to an Australian population. Marine Biology 138: 229-234. doi: 10.1007 / s002270000456
  17. ↑ Alexandre Meinesz, Thomas Belsher, Thierry Thibaut, Boris Antolic, Karim Ben Mustapha, Charles-Francois Boudouresque, Daniele Chiaverini, Francesco Cinelli, Jean-Michel Cottalorda, Aslam Djellouli, Amor El Abed, Carla Orestano, Antoni M. Grau, Ljiljana Ivesa , Andrej Jaklin, Habib Langar, Enric Massuti-Pascual, Andrea Peirano, Leonardo Tunesi, Jean de Vaugelas, Nevenka Zavodnik, Ante Zuljevic (2001): The introduced green alga Caulerpa taxifolia continues to spread in the Mediterranean. Biological Invasions 3: 201-210.
  18. ↑ I Meusnier, JL Olsen, WT Stam, C Destombe, M Valero: Phylogenetic analyzes of Caulerpa taxifolia (Chlorophyta) and of its associated bacterial microflora provide clues to the origin of the Mediterranean introduction. In: Molecular Ecology 10, 4, 2001: 931-946. doi: 10.1046 / j.1365-294x.2001.01245.x
  19. ↑ O. Jousson, J. Pawlowski, L. Zaninetti, FW Zechman, F. Dini, G. Di Giuseppe, R. Woodfield, A. Millar, A. Meinesz (2000): Invasive alga Reaches California. Nature 408: 157.
  20. ↑ Susan L. Williams & Stephanie L. Schroeder (2004): Eradication of the invasive seaweed Caulerpa taxifolia by chlorine bleach. Marine Ecology Progress Series 272: 69-76.
  21. ↑ Thierry Thibaut, Alexandre Meinesz, Philippe Amade, Stéphane Charrier, Kate De Angelis, Santina Ierardi, Luisa Mangialajo, Jennifer Melnick, Valérie Vidal (2001): Elysia subornata (Mollusca) a potential control agent of the alga Caulerpa taxifolia (Chlorophyta) in the Mediterranean Sea. Journal of the Marine Biological Association of the United Kingdom 81 (3): 497-504.
  22. ↑ Sandrine Ruitton, Marc Verlaque, Charles-Francois Boudouresque (2005). Seasonal changes of the Caulerpa racemosa var cylindracea Introduced (Caulerpales, Chlorophyta) at the northwest limit of its range Mediterranean. Aquatic Botany 82: 55-70. doi: 10.1016 / j.aquabot.2005.02.008
  23. ↑ HC Schröder, FA Badria, SN Ayyad, R Batel, M Wiens, HM Hassanein, B Kurelec, WE Müller: Inhibitory effects of extracts from the marine alga Caulerpa taxifolia and of toxin from Caulerpa racemosa on multixenobiotic resistance in the marine sponge Geodia cydonium . In: Environ Toxicol Pharmacol 5, 2, 1998: 119-126.
  24. ↑ Gérard Pergent, Charles-François Boudouresque Olivier Dumay, Christine Pergent-Martini, Sandy Wyllie-Echeverria: Competition between the invasive macrophyte Caulerpa taxifolia and the seagrass Posidonia oceanica: contrasting strategies. In: BMC Ecol 8, 2008: 20th PMC 2621152 (free full text)
  25. ↑ Tim M. Glasby (2013): Caulerpa taxifolia in seagrass meadows: killer or opportunistic weed? Biological Invasions 15: 1017-1035. doi: 10.1007 / s10530-012-0347-1
  26. ^ M Montefalcone, C. Morri, V. Parravicini, CN Bianchi (2015): A tale of two invaders: divergent spreading kinetics of the alien green algae Caulerpa taxifolia and Caulerpa cylindracea. Biological Invasions 17 (9): 2717-2728.
  27. ↑ Anna Maria Mannino & Paolo Balistreri (2014): An updated overview of invasive Caulerpa taxa in Sicily and circum-Sicilian Islands, strategic zones within the NW Mediterranean Sea. Flora Mediterranea 27: 221-240 doi: 10.7320 / FlMedit27.221
  28. ↑ Ljiljana Ivesa, Andrej Jaklin, Massimo Devescovi (2006): Vegetation patterns and spontaneous regression of Caulerpa taxifolia (Vahl) C. Agardh in Malinska (Northern Adriatic, Croatia). Aquatic Botany 85: 324-330. doi: 10.1016 / j.aquabot.2006.06.009

Web links

Commons : Caulerpa taxifolia  - collection of images, videos and audio files