Caulerpa

Caulerpa is a genus of seaweeds in the family Caulerpaceae (among the green algae). They are unusual because they consist of only one cell with many nuclei, making them among the biggest single cells in the world. A species in the Mediterranean can have a stolon more than 3 metres (9.8 ft) long, with up to 200 fronds. This species can be invasive from time to time.

Caulerpa
Caulerpa prolifera
Scientific classification
Phylum: Chlorophyta
Class: Ulvophyceae
Order: Bryopsidales
Family: Caulerpaceae
Genus: Caulerpa
J.V. Lamouroux, 1809
Type species
Caulerpa prolifera
(Forsskål) J.V. Lamouroux, 1809 [1]
Species[2]

About 86

Referring to its thalli's crawling habit, the name means 'stem (that) creeps', from the Ancient Greek kaulos (καυλός, ‘stalk’) and herpo (ἕρπω, ‘to creep’).[3]

Biology

Caulerpa supports its large size by having its cytoplasm circulate constantly, supported by a network of microtubules. This behavior was known in 1967.[4]

The cytoplasm does not leak out when the cell is cut. Regeneration is directional, with rhizoids at the bottom and fronds at the top.[5]

The genus produces a number of secondary metabolites thought to be related to its toxicity and peppery taste. These include the red pigment alkaloid caulerpin and its derivative caulerchlorin and the amine mixture caulerpicin.

Food use

Some species of Caulerpa are edible. The two most commonly eaten are Caulerpa lentillifera and Caulerpa racemosa, both called "sea grapes" in English. Both are traditionally harvested in the wild and sold in local markets in Southeast Asia, Oceania, and East Asia. They are eaten raw in salads and have a characteristic "sea" flavor and a crunchy texture.[6]

Only C. lentillifera is cultivated in aquaculture. Its cultivation began in the 1950s in Cebu, Philippines, after accidental introduction of C. lentillifera to fish ponds.[7] This was followed by Japan in 1986, where it was cultivated in tanks in the tropical waters of Okinawa.[8] Commercial cultivation has since spread to other countries, including Vietnam, Taiwan, and China (in Fujian and Hainan). Most are for domestic consumption, but they are also exported to Japan.[9]

Invasive behaviour

Another species, Caulerpa taxifolia, has become an invasive species in the Mediterranean Sea, Australia and southern California (where it has since been eradicated). In U.S. waters, the Mediterranean strain of Caulerpa taxifolia is listed as a federal noxious weed, under the Plant Protection Act. The Aquatic Nuisance Species Taskforce has also created a National Management Plan for the Genus Caulerpa. The state of California also prohibits possession of nine different species of Caulerpa.

It is thought that Caulerpa species have such invasive properties in these regions due to their capability to thrive in temperate waters, along with their freedom from natural predators. Most Caulerpa species evolved in tropical waters, where herbivores have immunity to toxic compounds (mainly caulerpicin) within the alga. Temperate water herbivores have no natural immunity to these toxins, allowing Caulerpa to grow unchecked if introduced to temperate waters.

C. racemosa has recently been found in waters around Crete, where it is thought to have contributed to a significant reduction in fisheries. The alga has invaded the area from the warmer waters of the Red Sea.

C. cylindracea, which is native to Australia, has also become an invasive species in the Mediterranean.[10]

Use in aquariums

Caulerpa is common in the aquarium hobby as a nitrate absorber because of its rapid growth under relatively adverse conditions. It may also be used in refugiums for a long-term nitrite absorber. Many introductions of invasive Caulerpa to the wild are thought to have occurred via aquarium dumping although there is no proof that this is so. For this reason, some aquarium hobbyists have begun using Chaetomorpha or an algae scrubber instead.[11][12]

Species
Oval sea grapes, Caulerpa racemosa var. clavifera, at 5 metres' depth
Feather algae, Caulerpa sertularioides at 11 metres' depth on ridge

The species currently recognized are:[1]

References
  1. Caulerpa J.V. Lamouroux, 1809 World Register of Marine Species. Retrieved 2011-08-20
  2. 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.
  3. Bold, Harold Charles; Wynne, Michael James (1985). Introduction to the algae. Prentice-Hall. p. 229. ISBN 9780134777467.
  4. Sabnis, DD; Jacobs, WP (December 1967). "Cytoplasmic streaming and microtubules in the coenocytic marine alga, Caulerpa prolifera". Journal of Cell Science. 2 (4): 465–72. PMID 6080540.
  5. Jacobs, William P. (December 1994). "Caulerpa". Scientific American. 271 (6): 100. Bibcode:1994SciAm.271f.100J. doi:10.1038/scientificamerican1294-100. This tropical alga is the world’s largest single-celled organism. Yet it di›erentiates into a complex structure of leaves, stems and roots.
  6. Paul, Nicholas A.; Neveux, Nicolas; Magnusson, Marie; de Nys, Rocky (21 December 2013). "Comparative production and nutritional value of "sea grapes" — the tropical green seaweeds Caulerpa lentillifera and C. racemosa". Journal of Applied Phycology. doi:10.1007/s10811-013-0227-9. S2CID 15745994.
  7. Trono, Gavino C., Jr. (December 1988). Manual on Seaweed Culture. ASEAN/UNDP/FAO Regional Small-Scale Coastal Fisheries Development Project.
  8. Trono, G.C., Jr. "Caulerpa lentillifera (PROSEA)". Pl@ntUse. PROSEA (Plant Resources of South East Asia). Retrieved 26 October 2020.
  9. Chen, Xiaolin; Sun, Yuhao; Liu, Hong; Liu, Song; Qin, Yukun; Li, Pengcheng (2019). "Advances in cultivation, wastewater treatment application, bioactive components of Caulerpa lentillifera and their biotechnological applications". PeerJ. 7: e6118. doi:10.7717/peerj.6118. PMC 6329336. PMID 30643691.
  10. Montefalcone, Monica; Morri, Carla; Parravicini, Valeriano; Bianchi, Carlo Nike (26 May 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. doi:10.1007/s10530-015-0908-1. S2CID 1973648.
  11. Nutrient Cycling In The Great Barrier Reef Aquarium. Proceedings of the 6th International Coral Reef Symposium, Australia, 1988, Vol. 2
  12. Reef Invertebrates, 2003, page 46

Further reading
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