DOI 10.1007/s00248-019-01332-8 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 (mean2014–2015 = 652 ± 179 μg 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.
Phytoplankton, Diversity, Cyanobacteria, Picoeukaryote, Extreme environment, Thalassohaline lake
| File | Pages | Size | Access | |
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Publisher's official version | 15 | 835 Ko | ||
Table S1 Cyanobacterial OTU affiliation obtained by alignment of 16S rDNA sequences with NCBI BLAST tool, Genbank Databases, and sequences from strains isolated from Lake Dziani Dzaha | 1 | 147 Ko | ||
Table S2 Plastid-related OTU affiliation obtained by alignment of 16S rDNA plastids sequences with NCBI BLAST tool, Genbank Databases, and plastids sequences from Phytoref | 1 | 11 Ko | ||
Table S3 Review of Arthrospira fusiformis (Cyanobacteria) and Picocystis salinarum (Chlorophyta) characteristics | 3 | 152 Ko | ||
Fig. S1 Cyanobacterial OTUs affiliation using consensus maximum likelihood phylogenetic tree based on 16S rRNA gene sequences of representative Cyanobacteria strains isolated from Dziani Dzaha ... | 1 | 374 Ko | ||
Fig. S2 Eukaryotic plastid-related OTUs affiliation using consensus Maximum Parsimony tree based on 16S rRNA gene sequences of photosynthetic-eukaryotes chloroplasts of representative sequences of... | 1 | 24 Ko | ||
Fig. S3 Light microscope micrographs of a environmental sample from Lake Dziani Dzaha (DZ-15-11 campaign) with Arthrospira fusiformis straight filaments and unicellular cells of ... | 1 | 239 Ko | ||
Fig. S4 Comparison of normalized sequences number with the cells abundance (cells mL−1) for the two dominant taxa: Arthrospira fusiformis and Picocystis salinarum. Data all the four campaigns ... | 1 | 412 Ko |
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