par Lancelot, Christiane ;Rousseau, Véronique
Editeur scientifique Green, J.C.;Leadbeater, B.S.C.
Référence The Haptophyte Algae, Oxford University Press, Vol. 12, Ed. out of print, page (229-245)
Publication Publié, 1994
Partie d'ouvrage collectif
Résumé : Species of Phaeocystis exhibit phase alternation between individual cells and gelatinous colonies. They reguiarly form dense, nearly specific blooms, in very contrasting nutrient-rich areas of the world's oceans. The uniqueness of this genus of marine phytoplankters rests not only in its ubiquity but mostly in its peculiar physiology and ecology. No other marine phytoplankter has ever been shown to dominate an entire ecosystem; no other marine species distinguishes itself by a complex polymorphic life cycle that induces dramatic changes in the structure and functioning of planktonic and benthic food-webs as well as in the biogeochemistry of trace elements. The main features of the ecology of Phaeocystis-dominated ecosystems are analysed with regard to the Phaeocystis life cycle, and to recent data on the biochemistry and nutrient (major and trace element) metabolism of the different morphological forms that succeed each other during Phaeocystis bloom development, in relationship to the behaviour of bacteria and micro-, meso-, and meta-zooplankton and the physical structure of the marine habitat. Particular emphasis is given ta the biological functioning of Phaeocystis colonies that constitute by far the most important morphological forms in natural environments, as determined from the analysis of the structure and function of the 'mucilaginous matrix embedding the cells. Evidence is presented that the most remarkable ecological and biogeochemical properties of Phaeocystis-dominated ecosystems are attributable to the capacity of Phaeocystis colonial cells to synthesize, in nutrient-deprived conditions, exopolysaccharides capable of gelation.

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