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Physical, chemical, and microbiological characteristics of microbial mats (KOPARA) in the South Pacific atolls of French Polynesia

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Microbial mats that develop in shallow brackish and hyposaline ponds in the rims of two French polynesian atolls (Rangiroa and Tetiaroa) were intensively investigated during the past three years. Comparative assessment of these mats (called kopara in polynesian language) showed remarkable similarities in their composition and structure. Due to the lack of iron, the color of the cyanobacterial pigments produced remained visible through the entire depth of the mats (20–40 cm depth), with alternate green, purple, and pink layers. Profiles of oxygen, sulfide, pH, and redox showed the anoxia of all mats from a depth of 2–3 mm. Analyses of bacterial pigments and bacterial lipids showed that all mats consisted of stratified layers of cyanobacteria (mainly Phormidium, Schizothrix, Scytonema) and purple and green phototrophic bacteria. The purple and green phototrophic bacteria cohabit with sulfate reducers (Desulfovibrio and Desulfobacter) and other heterotrophic bacteria. The microscopic bacterial determination emphasized the influence of salinity on the bacterial diversity, with higher diversity at low salinity, mainly for purple nonsulfur bacteria. Analyses of organic material and of exopolymers were also undertaken. Difference and similarities between mats from geomorphological, microbiological, and chemical points of view are discussed to provide multicriteria of classification of mats.Key words: microbial mats, cyanobacteria, bacterial pigments, French Polynesia atolls, exopolymers.

Les tapis microbiens qui se développent dans des mares saumâtres et hyposalines en pourtour de deux atolls de la Polynésie Française (Rangiroa et Tetiaroa) ont été étudiés intensivement au cours des trois dernières années. Un suivi comparatif de ces tapis (appelés kopara en Polynésien) a montré des similitudes remarquables dans leur composition et leur structure. À cause de l'absence de fer, la couleur des pigments reste visible dans toute la profondeur des tapis (20 à 40 cm de profondeur), avec des alternances de vert, pourpre et rose. Les profils d'oxygène, de sulfure et de redox montrèrent l'anoxie des tapis dès 2 à 3 mm de profondeur. Les analyses des pigments et des lipides bactériens ont montré que tous les tapis consistaient en des couches stratifiées de cyanobactéries (principalement Phormidium, Schizothrix et Scytonema) et de bactéries phototrophes pourpres et vertes. Ces dernières cohabitent avec des bactéries sulfato-réductrices (Desulfovibrio et Desulfobacter) ainsi que d'autres bactéries hétérotrophes. Les observations microscopiques ont montré l'influence de la salinité sur la diversité bactérienne des différents tapis principalement pour les bactéries pourpres non sulfureuses. Des analyses de matériaux organiques et d'exopolymères ont également été réalisées. Les différences et les similitudes entre les tapis sont discutées du point de vue géomorphologique, chimique et microbiologique de façon à fournir des critères de classification des tapis microbiens de Polynésie.Mots clés : tapis microbiens, cyanobactéries, pigments bactériens, atolls de la Polynésie Française, exopolymères.[Traduit par la Rédaction]

Keywords: French Polynesia atolls; atolls de la Polynésie Française; bacterial pigments; cyanobacteria; cyanobactéries; exopolymers; exopolymères; microbial mats; pigments bactériens; tapis microbiens

Document Type: Research Article

Publication date: 2001-11-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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