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

Abstract

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.

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“…A final possible source of variability stems from the complex interconnection between primary production and respiration within bacterial mats. Layers of Kiritimati mat communities are distinct groups with upper surface layers consisting mainly of sheath pigments absorbing 350–450 nm wavelengths, and deeper layers showing pigments characteristic of anoxic purple and green bacteria [ 18 , 19 ]. These communities are likely consortia; a characteristic which permits the cycling of potentially limiting nutrients and which often forms closely spaced micro-niches [ 20 , 21 ].…”

Irradiance Regulation of Photosynthesis and Respiration in Modern Marine Microbialites Built by Benthic Cyanobacteria in a Tropical Lagoon (New Caledonia)

“…While in temperate climates, large living microbial mats and microbialites are mostly restricted to so-called extreme environments where grazing pressure is reduced [27], in brackish and marine tropical environments these microbial structures are probably more widespread. Indeed, microbial mats cover large surface areas in Polynesian brackish ponds [37], and microbialites built by cyanobacteria are common in tropical lagoons such as those described for French Polynesia [45] and in New Caledonia (Camoin and Golubic, unpublished results). The taxonomy of microbialite-forming cyanobacteria in French Polynesia has been studied using a polyphasic approach [1,2].…”

Exploring benthic cyanobacterial diversity and co-occurring potentially harmful dinoflagellates in six islands of the South Pacific

“…The global distribution of marine planktonic cyanobacteria and their important contribution to nitrogen-fixation in the ocean is well known (Zehr et al 2001;Lesser et al 2007), but considerably less attention has been given to benthic cyanobacterial communities in coastal areas (Bauer et al 2008). In the South Pacific, microbial mats consisting of stratified layers of cyanobacteria, mainly Phormidium, Schizothrix, Scytonema and purple and green phototrophic bacteria have been observed in French Polynesian atolls (Che et al 2001).…”