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''Phaeocystis'' is a genus of algae belonging to the Prymnesiophyte class and to the larger division of Haptophyta. It is a widespread marine phytoplankton and can function at a wide range of temperatures (eurythermal) and salinities (euryhaline). Members of this genus live in the open ocean, as well as in sea ice. It has a polymorphic life cycle, ranging from free-living cells to large colonies.〔 The ability to form a floating colony is one of the unique attributes of ''Phaeocystis'' – hundreds of cells are embedded in a polysaccharide gel matrix, which can increase massively in size during blooms.〔 The largest ''Phaeocystis'' blooms form in the polar seas: ''P. pouchetii'' in the north and ''P. antarctica'' in the south.〔 This intense ''Phaeocystis'' productivity generally persists for about a three-month period, spanning most of the summer in the Southern Hemisphere. ''Phaeocystis''-abundant ecosystems are generally associated with commercially important stocks of crustaceans, molluscs, fish and mammals. ''Phaeocystis'' may have negative effects on higher trophic levels in the marine ecosystem, and consequent impacts on human activities (such as fish farming and coastal tourism), by forming odorous foams on beaches during the wane of a bloom. The ability to form large blooms and its ubiquity make ''Phaeocystis'' an important contributor to the ocean carbon cycle. In addition, ''Phaeocystis'' produces dimethyl sulfide (DMS), a key player in the sulfur cycle.〔Stefels, J., Van Boekel, W.H.M., 1993. Production of DMS from dissolved DMSP in axenic cultures of the marine phytoplankton species ''Phaeocystis sp''., Mar. Ecol. Prog. Ser. 97, 11 –18.〕 == Distribution and life cycle == Free-living forms of ''Phaeocystis'' are globally distributed and occur in a variety of marine habitats, including coastal oceans, open oceans, polar seas and sea ice.〔Thomsen, H.A., Buck, K.R., Chavez, F.P., 1994. Haptophytes as components of marine phytoplankton., In: Green, J.C., Leadbeater, B.S.C. (Eds.), The Haptophyte Algae. Clarendon Press, Oxford, UK, pp. 187– 208.〕 Six species are currently assigned to the genus: ''P. antarctica'', ''P. jahnii'', ''P. globosa'', ''P. pouchetti'', ''P. scrobiculata'' and ''P. cordata''. Three species (''P. globosa'', ''P. pouchetii'', and ''P. antarctica'') are associated with bloom formation in nutrient-rich areas,〔Lancelot, C., Keller, M.D., Rousseau, V., Smith Jr., W.O., Mathot, S., 1998. Autecology of the marine haptophyte ''Phaeocystis sp''., In: Anderson, D.M., Cembella, A.D., Hallagraeff, G.M. (Eds.), Physiological Ecology of Harmful Algal blooms, vol. 41. Springer-Verlag, Berlin, pp. 209–224.〕 which can occur either naturally (e.g. in the Ross Sea, Greenland Sea or the Barents Sea) or due to anthropogenic inputs (e.g. in the Southern Bight of the North Sea or the Persian Gulf). Generally, ''P. globosa'' blooms in temperate and tropical waters, whereas ''P. pouchetii'' and ''P. antarctica'' are better adjusted to the cold temperatures prevailing in Arctic and Antarctic waters, respectively. However, ''P. pouchetii'' also tolerates warmer temperatures and has been seen in temperate waters. Genome comparison has shown that the RUBISCO spacer region (located in the plastid DNA, between two subunits of the enzyme 1,5 -isphosphate carboxylase) is highly conserved among closely related colonial ''Phaeocystis'' species and identical in ''P. antarctica'', ''P. pouchetii'' and two warm-temperate strains of ''P. globosa'', with a single base substitution in two cold-temperate strains of ''P. globosa''. ''Phaeocystis'' can exist as either free-living cells or colonies. Free-living cells can show a variety of morphologies, depending on the species. All species can exist as scaly flagellates, and this is the only form that has been observed for ''P. scrobiculata'' and ''P. cordata''. Three species have been observed as colonies (''P. globosa'', ''P. pouchetii'' and ''P. antarctica'') and these can also exist as a flagellate devoid of scales and filaments.〔 In colonies of ''Phaeocystis'', the colony skin may provide protection against smaller zooplankton grazers and viruses. While suspected in other species (''P. pouchetii'' and ''P. antarctica''), a haploid-diploid life cycle has only been observed in ''P. globosa''. In this cycle, sexual reproduction is dominant in colony bloom formation/termination, and two types of vegetative reproduction exist. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Phaeocystis」の詳細全文を読む スポンサード リンク
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