Persistence and stability of phytoplankton communities in eutrophic reservoirs of northeastern Brazil

Abstract

In this study, the structure of phytoplankton communities in reservoirs with constant cyanobacteria blooms was evaluated using stability, persistence and species richness analyses. Samples were collected monthly from three reservoirs in northeastern Brazil between February 2012 and January 2013. The phytoplankton taxa were quantified under an inverted microscope. Stability was measured using Spearman's coefficient, based on the analysis of abundance rankings; persistence was measured using the inverse calculation for turnover; and richness was calculated using the number of species. Statistical analyses were used to determine the influence of abiotic variables on persistence and stability, and correlations were performed between persistence and stability and between species richness and stability. Cyanobacteria, particularly Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju, were observed in all samples. The results showed that stability and persistence were high, whereas species richness was low in the reservoir communities. The nutrients nitrate, nitrite and orthophosphate influenced persistence, whereas pH and ammonium explained stability. Persistence and stability were not significantly correlated, but a negative correlation was observed between species richness and stability.

Sodium and nitrate favor the steady state of cyanobacteria in a semiarid ecosystem

“…Volume reduction, water column stability and long water retention time in the reservoirs combined with drought would have created excellent conditions of temperature and irradiation for the dominance of Cylindrospermopsis sp. Studies carried out by Tavares et al (2017) also showed that the high nutrient concentrations (nitrate, nitrite and orthophosphate) influenced persistence of C. raciborskii throughout the study in semiarid reservoirs in Brazil.…”

“…Despite these traits, studies in semiarid regions addressing the occurrence of steady state, considering all the pre-requisites established by Sommer et al (1993), are scarce. Instead, authors have attempted to explain the factors leading to the dominance and persistence of phytoplankton species in these ecosystems, carrying out studies with monthly samplings (Moura, Oliveira, Dantas, & Arruda-Neto, 2007;Dantas, Moura, & Oliveira, 2011;Tavares, Moura, & Dantas, 2017), so it is not possible to apply the concept of steady state in these studies.…”