Avaliação dos efeitos da salinidade no crescimento e na interação de Nannochloropsis sp. (Eustigmatophyceae) e Diacronema sp. (Pavlovophyceae) isoladas da Lagoa Rodrigo de Freitas, RJ

Abstract

The Rodrigo de Freitas Lagoon (RFL) is incorporated into the urban area and, consequently, is impacted by anthropic activities, especially the intense discharge of domestic effluents in its drainage basin, which has led to its eutrophication. This process is responsible for frequent microalgae blooming events that often result in episodes of fish mortality. Among the phytoplankton species present in the RFL, we highlight in this work Nannochloropsis sp. (Eustigmatophyceae) and Diacronema sp. (Pavlovophyceae), which presented a relevant contribution in 2012, both of which are involved in consecutive flowering events. Knowledge about the ecophysiology of species of these genera, considering the dynamics of environmental variables, such as salinity, is fundamental for understanding the main control mechanisms of these blooms. In order to investigate the influence of salinity on growth and interaction between three strains of Nannochlorospsis sp (NN-M, NN-J and NN-S) and one of Diacronema sp. (DI), tests were performed on f / 2 medium, containing or not exudates of the competing species in three salinities (8S, 14S and 20S). Growth rate (μ) and maximum yield (Rmax) were measured with the increase of chlorophyll a, as well as evaluation of the effective quantum yield (ɸPSII) and fast light curve parameters (FLC: α, ETRmax and EK). The strains DI and NN-S obtained better growth rates in 14S (μ = 0,93 / Rmax = 30.12 and μ = 0,38 / Rmax = 91,24), being restricted to a lower salinity fluctuation interval (Stenohalins). While NN-M and NN-J strains showed no differences in their rates for the salinities tested, they had a higher amplitude of salinity variation (eurialines), however larger Rmax were observed in 14S (Rmax = 351,1 and Rmax = 496,4). Thus, the strains of Nannochloropsis sp. Presented intraspecific variability in the physiological response to the tested variable. In the interaction tests, the NN-S and DI strains showed allelochemical activity, which was demonstrated by inhibition (NN-S exudate) and stimulus (DI exudate) of the growth rates of the competing species, as well as changes in the quantum yield values (ɸPSII) and the CRL parameters. A tendency to increase the values of FLC parameters during the course of the interaction experiment with the NN-S strain was observed, suggesting the idea of attenuation of the action of the allelochemical contained in the DI exudate