Aggregating anemone 2066774 217647955 2008-06-07T00:07:20Z Aequorea 7165707 /* Predation */ {{Taxobox | name = Aggregating anemone | image = Anthopleura elegantissima.jpg | image_width = 240px | regnum = [[Animal]]ia | phylum = [[Cnidaria]] | classis = [[Coral|Anthozoa]] | subclassis = [[Hexacorallia]] | ordo = [[Actiniaria]] | subordo = [[Nyantheae]] | infraordo = [[Thenaria]] | familia = [[Actiniidae]] | genus = ''[[Anthopleura]]'' | species = '''''A. elegantissima''''' | binomial = ''Anthopleura elegantissima'' | binomial_authority = ([[Johann Friedrich von Brandt|Brandt]], 1835) }} '''''Anthopleura elegantissima''''', also known as the '''aggregating anemone''' or '''clonal anemone''', is the most abundant [[species]] of [[sea anemone]] found on rocky, tide swept shores along the Pacific coast of North America. <ref>Kozloff, Eugene N.. Marine Invertebrates of the Pacific Northwest. 2nd. Seattle: University of Washington Press, 1996.</ref>. This [[cnidarian]] hosts endosymbiotic [[algae]] called [[zooxanthellae]] that contribute substantially to [[primary productivity]] in the [[intertidal zone]].<ref>Fitt, W. K., R. L. Pardy, AND M. M. Luttker. 1982. Photosynthesis, respiration, and contribution to community productivity of the symbiotic sea anemone Anthopleura elegantissima. J. Exp. Mar. Biol. Ecol. 61: 213–232.</ref> ''A. elegantissima'' has become a model organism for the study of temperate cnidarian-algal symbioses. ==Description== The polyps of ''Anthopleura elegantissima'' reach up to 8 cm across the oral disk with approximately 100 tentacles in 3-4 rows around the margins of the oral disk. Most are olive to bright green (depending on the species of algal symbionts present) with tentacles tipped in pink. Individuals that live in microhabitats that are deficient in [[photosynthetically active radiation]] (PAR), such as under docks or in caves, lack symbionts and are pale yellow to white in color <ref>Secord D, Muller-Parker G (2005) Symbiont distribution along a light gradient within an intertidal cave. Limnology and Oceanography 50: 272-278</ref>. ==Range== Pacific coast of North America from Alaska, USA to Baja California, Mexico ==Life History== This species of anemone is capable of reproducing both sexually and asexually. As adults, ''A. elegantissima'' release gametes into the water that join to form genetically unique individuals that settle on intertidal rock. This genetically distinct individual can then proliferate through [[binary fission]]. Some argue that this is not true reproduction but actually a form of growth <ref>Pearse, J.S., Pearse, V.B. & Newberry, A.T. 1989. Telling sex from growth: dissolving Maybard Smith's paradox. Bulletin of Marine Science. 45:433-436.</ref>. Fission is often prompted in the autumn by a decrease in the abundance of food and follows sexual spawning in summer <ref>Sebens, K.B. 1980. The regulation of asexual reproduction and indeterminate body size in the sea anemone ''Anthopleura elegantissima'' (Brandt). Biological Bulletin. 158:370-382</ref><ref>Sebens, K.B. 1981b. Reproductive ecology of the intertidal sea anemones ''Anthopleura xanthogrammica'' (Brandt) and ''Anthopleura elegantissima'' (Brandt): body size, habitat, and sexual reproduction. Journal of Experimental Marine Biology and Ecology. 54:225-250.</ref>. Over time, a single individual can generate a large colony of genetically identical [[polyps]]. Because of its ability to grow in this manner, the genetic entity of a colony is potentially immortal on an ecological time scale. ==Natural History== ===Photosynthetic Symbiosis=== ''Anthopleura elegantissima'' hosts [[endosymbiotic]], photosynthetic algae in the tentacles, oral disk and column of the polyps. In addition to a [[chlorophyte]], two species of [[dinoflagellates]] are known to inhabit the anemone: ''Symbiodinium muscatinei'' and ''S. californium'' <ref>Muller-Parker G, Pierce-Cravens J, Bingham BL (2007) Broad thermal tolerance of the symbiotic dinoflagellate Symbiodinium muscatinei (Dinophyta) in the sea anemone Anthopleura elegantissima (Cnidaria) from northern latitudes. Journal of Phycology 43:25-31 </ref>. These algae are generally referred to as [[zooxanthellae]] (dinoflagellates) and zoochlorellae (chlorophytes) and many polyps concurrently host more than one type of alga within their tissues. The rate of occurrence of each alga is determined by temperature and light regimes of anemone habitats <ref>SAUNDERS, B., AND G. MULLER-PARKER. 1997. The effects of temperature and light on two algal populations in the temperate sea anemone Anthopleura elegantissima (Brandt, 1835). J. Exp. Mar. Biol. Ecol. 211: 213–224.</ref>. Zoochlorellae are typically found at higher latitudes and in deeper intertidal habitats than zooxanthellae. <ref>Secord D, Augustine L (2000) Biogeography and microhabitat variation in temperate algal-invertebrate symbioses: zooxanthellae and zoochlorellae in two Pacific intertidal sea anemones, Anthopleura elegantissima and A. xanthogrammica. Invertebrate Biology 119:139-146</ref>. Of the two species of zooxanthellae that inhabit the anemone, ''S. californium'' is restricted to southern California due to its intolerance of cold temperatures whereas ''S. muscatinei'' is tolerant of a broad range of temperature and irradiance levels. The [[mutualistic]] relationship of these organisms requires adaptations of each partner. The algal symbionts convert inorganic carbon into carbohydrates for use by each partner and release oxygen to the animal host in the process. To accommodate the algae, the anemone must provide concentrated carbon dioxide to their intracellular photosynthetic guests as well as [[PAR]] to fuel the photosynthetic process. This restricts the symbiotic organism to [[euphotic]] habitats and requires consistent exposure to high levels of [[ultraviolet radiation]] (UVR). To protect from potentially damaging UVR, the algae provide mycosporine-like amino acids (MAAs) that act as sunscreen for themselves and the host <ref>Shick, J. M., W. C. Dunlap, J. S. Pearse, and V. B. Pearse. 2002. Mycosporine-like amino acid content in four species of sea anemones in the genus Anthopleura reflects phylogenetic but not environmental or symbiotic relationships. Biol. Bull. 203: 315–330.</ref>. The anemones, in turn, produce antioxidants called superoxide dismutases to protect against reactive oxygen that causes oxidative stress <ref>Dykens, J. A. and J. M. Shick. 1982. Oxygen production by endosymbiotic algae controls superoxide dismutase activity in their animal host. Nature 297:579–580.</ref><ref>Dykens, J. A., J. M. Shick, C. Benoit, G. R. Buettner, and G. W. Winston. 1992. Oxygen radical production in the sea anemone Anthopleura elegantissima and its endosymbiotic algae. J. Exp. Biol. 168:219–41.</ref> ===Agonism Between Colonies=== ''Anthopleura elegantissima'' is agonistic toward other individuals with different genetic disposition. When one colony of genetically identical polyps encounters a different genetic colony, the two will wage territorial battles. ''A. elegantissima'' has specialized tentacles called acrorhagi that are used solely to deter other colonies from encroaching on their space. When a polyp makes physical contact with a non-clonemate, it extends the acrorhagi to attack the competing anemone with stinging cells called [[nematocysts]]. Acrorhagi of the attacking anemone leave behind a 'peel' of the [[ectoderm]] and nematocysts that causes tissue necrosis in the receiving animal. A study of two colonies on a boulder removed from the shore and brought into a laboratory revealed that hostilities between neighboring colonies follow the tides. As water rushed into the tank, warrior polyps inflated their acrorhagi, tripled their body length and began reaching into an empty swath of rock between the colonies. Occasionally, a polyp from one of the colonies would move into the spatial zone between the two colonies, acting as a scout, and would be attacked by the warrior polyps of the other clone. If the scout polyp received enough stings, it would be attacked by its clonemates upon return to its own colony. The return of an attacked scout to the clone with acrorhagial peel may serve to communicate the presence and identity of neighboring clones to the interior of the colony <ref>Ayre DJ, Grosberg RK (2005) Behind anemone lines: factors affecting division of labour in the social cnidarian Anthopleura elegantissima. Animal Behaviour 70:97-110</ref>. ==Predators== The few known predators of ''Anthopleura elegantissima'' include the nudibranch ''Aeolidia papillosa'', leather star ''Dermasterias imbricata'' and mosshead sculpin ''Clinocottus globiceps''. [[Category:Anthozoa]] [[fr:Anthopleura elegantissima]] ==Footnotes== {{Reflist}}