Main content area

Spatiotemporal variability of cyanobacterial community in a Brazilian oligomesotrophic reservoir: The picocyanobacterial dominance

Batista, Ana Maria M., Giani, Alessandra
International journal of ecohydrology & hydrobiology 2019
Cyanobacteria, biomass, community structure, dams (hydrology), denaturing gradient gel electrophoresis, dry season, eutrophication, nutrient content, phytoplankton, rivers, seasonal variation, spatial variation, temperature, wet season, Brazil
The spatiotemporal variability of the cyanobacteria community was studied in Volta Grande reservoir (Brazil) during 12 months in five sampling sites. The sites followed a spatial gradient, from the river inflow to the dam. To evaluate the molecular diversity of the community, we used the fingerprinting method DGGE (Denaturing Gradient Gel Electrophoresis), and at the same time taxonomic analyses based on species morphology were performed under inverted microscope. The most important genera were assembled in three groups: picocyanobacteria, filamentous cyanobacteria and Microstistis species. Picocyanobacteria belong to a group known for smaller cell size, were observed in all five sampling sites and were dominant especially in sites closer to the dam or in the transition zone. Filamentous cyanobacteria were mainly found closer to the river inflow. A seasonal variation was detected, with higher picocyanobacterial biomass during the rainy season, while nanoplanktonic species were more common in the dry season. Thus, the reservoir showed spatial and temporal variability in the phytoplankton community composition. These patterns were related to variations observed in nutrient concentration and temperature. Picocyanobacteria were a very important part of the phytoplankton community and represented on average 85% of total cyanobacteria biomass. The morphological technique revealed higher diversity than the molecular method possibly because of the low number of deposited sequences available for picocyanobacteria. The oligomesotrophic status observed in Volta Grande reservoir was most likely the main factor responsible for the dominance of this group since the relative importance of picocyanobacteria increases in less eutrophic environments.