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. 2019 Oct;78(3):603-617.
doi: 10.1007/s00248-019-01332-8. Epub 2019 Feb 7.

Very Low Phytoplankton Diversity in a Tropical Saline-Alkaline Lake, with Co-dominance of Arthrospira fusiformis (Cyanobacteria) and Picocystis salinarum (Chlorophyta)

C Bernard  1 , A Escalas  2 , N Villeriot  2   3 , H Agogué  4 , M Hugoni  5 , C Duval  2 , C Carré  3 , P Got  3 , G Sarazin  6 , D Jézéquel  6 , C Leboulanger  3 , V Grossi  7 , M Ader  6 , M Troussellier  3
Affiliations

Very Low Phytoplankton Diversity in a Tropical Saline-Alkaline Lake, with Co-dominance of Arthrospira fusiformis (Cyanobacteria) and Picocystis salinarum (Chlorophyta)

C Bernard et al. Microb Ecol. 2019 Oct.

Abstract

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.

Keywords: Cyanobacteria; Diversity; Extreme environment; Phytoplankton; Picoeukaryote; Thalassohaline lake.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Lake Dziani Dzaha (Mayotte Island) is an isolated, round crater lake with an area of approximately 0.25 km2 (a, b). The bathymetric map showed a mean depth of approximately 4 m and an 18-m deep pit, located in the eastern part of the lake (c). b, right picture: ©M. Troussellier, CNRS
Fig. 2
Fig. 2
Changes in the main physico-chemical characteristics (temperature, salinity, soluble sulfide (H2S), and oxygen saturation (%O2) as a function of depth and sampling campaign. April 2014 and 2015: stratified water column, end of the rainy season. October 2014 and November 2015: non-stratified period, end of the dry season
Fig. 3
Fig. 3
Changes in the abundance of Picocystis salinarum (open squares) and Arthrospira fusiformis (gray circles) as a function of depth during the four sampling campaigns. The abundance of P. salinarum and A. fusiformis was estimated by flow cytometry and microscopy, respectively
See this image and copyright information in PMC

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