Bernard C. auteur aut IRD Escalas A. auteur aut IRD Villeriot N. auteur aut IRD Agogue H. auteur aut IRD Hugoni M. auteur aut IRD Duval C. auteur aut IRD Carré Claire auteur aut IRD Got P. auteur aut IRD Sarazin G. auteur aut IRD Jezequel D. auteur aut IRD Leboulanger Christophe auteur aut IRD Grossi V. auteur aut IRD Ader M. auteur aut IRD Troussellier M. auteur aut IRD text journalArticle eng text/pdf reformatted digital access Lake Dziani Dzaha (Mayotte Island, Indian Ocean) is a tropical thalassohaline lake which geochemical and biological conditions make it a unique aquatic ecosystem considered as a modern analogue of Precambrian environments. In the present study, we focused on the diversity of phytoplanktonic communities, which produce very high and stable biomass (mean(2014-2015) = 652 +/- 179 mu g chlorophyll a L-1). As predicted by classical community ecology paradigms, and as observed in similar environments, a single species is expected to dominate the phytoplanktonic communities. To test this hypothesis, we sampled water column in the deepest part of the lake (18 m) during rainy and dry seasons for two consecutive years. Phytoplanktonic communities were characterized using a combination of metagenomic, microscopy-based and flow cytometry approaches, and we used statistical modeling to identify the environmental factors determining the abundance of dominant organisms. As hypothesized, the overall diversity of the phytoplanktonic communities was very low (15 OTUs), but we observed a co-dominance of two, and not only one, OTUs, viz., Arthrospira fusiformis (Cyanobacteria) and Picocystis salinarum (Chlorophyta). We observed a decrease in the abundance of these co-dominant taxa along the depth profile and identified the adverse environmental factors driving this decline. The functional traits measured on isolated strains of these two taxa (i.e., size, pigment composition, and concentration) are then compared and discussed to explain their capacity to cope with the extreme environmental conditions encountered in the aphotic, anoxic, and sulfidic layers of the water column of Lake Dziani Dzaha. specialized Phytoplankton Diversity Cyanobacteria Picoeukaryote Extreme environment Thalassohaline lake OCEAN INDIEN MAYOTTE COMORES 036 034 78 3 603-617 2019 0095-3628 https://www.documentation.ird.fr/hor/fdi:010077025 10.1007/s00248-019-01332-8 0095-3628 [F B010077025] https://www.documentation.ird.fr/hor/fdi:010077025 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers19-10/010077025.pdf IRD - Base Horizon / Pleins textes 2019-11-05 2025-02-24 fdi:010077025 fre