Spatial and temporal variation of the phytoplankton structure in cascading oligotrophic reservoirs of southeast Brazil

Abstract

Aim Structural changes in phytoplankton was evaluated in one ultraoligotrophic and two oligotrophic cascading reservoirs during two climatic periods (austral winter and summer) of 2014. Changes in phytoplankton biomass, species composition, and codons (functional groups) were evaluated along a vertical and a longitudinal profile. Methods Four sampling sites were selected for the first reservoir in the cascade (Cachoeira do França) and three for each of the other two reservoirs (Cachoeira da Fumaça and Serraria). Samples were collected along a vertical and a longitudinal profile. Species biomass and codons ‘sensu’ Reynolds were identified and expressed in terms of biomass. Results 18 codons were identified and associated to the reservoirs’ limnological conditions. Composition and biomass of descriptor species changed among seasons. Codon B consisting mainly of Discostella stelligera was the most frequent in all reservoirs in both climatic seasons. Conclusions Our findings showed that seasonality was the key factor for the species composition and phytoplankton codons changes. However, the cascade effect on phytoplankton structure was shown by the continuous contribution of Ceratium furcoides (codon LM) during the winter, and of Discostella stelligera (codon B) in both sampling periods in all three reservoirs.

Main predictors of phytoplankton occurrence in lotic ecosystems

“…The dynamics of phytoplankton metacommunities has received increasing attention in Brazilian scientific studies, however, floodplains (Devercelli et al, 2016;Diniz et al, 2023) and lentic environments, such as lakes or reservoirs (e.g., Bortolini et al, 2017Bortolini et al, , 2019Wojciechowski et al, 2017;Rodrigues et al, 2018;Loaiza-Restano et al, 2020), are addressed more frequently. The phytoplankton present in lotic environments is still poorly explored (Huang et al, 2023).…”