The small eukaryotes of great tropical African lakes: biodiversity, abundance and importance in the food web

FERMANI, P; DESCY, J.P.; MASSANA, R; METZ, SEBASTIÁN; MORANA, C.; SARMENTO, H.; BALAGUÉ, V; LOGARES, R.

Valparaíso

Congreso; Primer Congreso ISME América Latina; 2019

The lakes of East African Valley are unique natural resources that are heavily utilized by their bordering countries. Due to their large size, ecosystem function is dominated by pelagic processes, where microorganisms are key components of aquatic communities. Exploitation of resources, eutrophication and climate change is altering the diversity and function of these lakes and their microbial diversity is barely known, despite their importance in biogeochemical cycles. We investigated the community composition of small eukaryotes (< 5 µm) of four African great lakes (Kivu, Edward, Albert and Victoria) by sequencing the V4 region of 18S rRNA gene. Moreover, in the meromictic Lake Kivu, one of the largest methane reservoirs on Earth, two stations (Gisenyi and Ishungu) were sampled over vertical profiles. We obtained 779 operational taxonomic units (OTUs) (99% clustering similarity) grouped in 9 high-rank supergroups and 58 taxonomic classes, being Alveolata (31%), Opistokonta (20%) and Stramenopiles (17%) the most represented supergroups. In surface waters, microeukaryotes abundances differed amongst lakes according to physical and chemical variables. The cluster analysis (Bray-Curtis dissimilarity index) showed Lake Victoria, which presented the lowest abundances and the greater species richness, as the most distinct. Lake Kivu exhibited the highest abundance at 15 m in both sites, but differed in composition. Overall, we found many OTUs (40.6%) with low similarity (< 90%) with reported sequences in public databases, mostly in deep anoxic waters of Lake Kivu, suggesting a high potential for novel diversity, probably associated with their particular physical and chemical characteristics.