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

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.Electronic supplementary materialThe online version of this article (10.1007/s00248-019-01332-8) contains supplementary material, which is available to authorized users.

Morphology and Ecology of Two New Amoebae, Isolated From a Thalassohaline Lake, Dziani Dzaha

“…The thalassohaline lake of Dziani dzaha is considered an extreme environment of interest as it mimics environmental conditions that could be found in Precambrian oceans (Bernard et al, 2019). It could thus provide a window into early adaptation of microorganisms to such environmental conditions.…”

“…In previous studies, it has been reported that the season and/or the depth in the lake can influence its microbial diversity (Bernard et al, 2019;Hugoni et al, 2018). To see whether the two FLA isolates were influenced by these parameters, we performed a specific qPCR on DNA isolated from the water lake sampled in April (end of the rainy season) and November (dry season) 2015.…”

“…The spirulina Arthrospira fusiformis is the most abundant cyanobacterium in the lake, accounting for 95 % of the total photosynthetic biomass (Bernard et al, 2019). Its presence has been positively correlated with the temperature (Bernard et al, 2019).…”

“…The spirulina Arthrospira fusiformis is the most abundant cyanobacterium in the lake, accounting for 95 % of the total photosynthetic biomass (Bernard et al, 2019). Its presence has been positively correlated with the temperature (Bernard et al, 2019). As the highest temperatures, as well as highest light intensity, were found in the upper layer of the water column (first three meters), A. fusiformis is mainly found within this level.…”

Ecophysiology of a successful phytoplankton competitor in the African flamingo lakes: the green alga Picocystis salinarum (Picocystophyceae)

“…Picocystis strains have also been recorded in several other saline waterbodies: in North Africa (Rihab et al 2017); in the North American region; in Mono Lake, USA (Roesler et al 2002); in the South American region; in Peru (Tarazona Delgado et al 2017); in an Asian soda lake in Inner Mongolia (Hollibaugh et al 2001;Fanjing et al 2009); in Lake Sambhar, India (Krienitz 2018); and in Lake Dziani Dzaha (Mayotte Island, Indian Ocean; Cellamare et al 2018;Bernard et al 2019). Phylogenetic analysis of strains from Africa and India revealed that all the strains belong to one and the same species, Picocystis salinarum.…”