Changes in phytoplankton spatial and temporal dynamics in a Brazilian tropical oligotrophic reservoir after net cage installation

Abstract

This study analyzed the phytoplankton community response and the spatial and temporal variation of abiotic variables caused by fish farming in net cages installed in Ilha Solteira reservoir, São Paulo, Brazil. Water samples were collected monthly (August 2011-July 2013), from the subsurface, at three sites: upstream from farming area (S1), farming area (S2), and downstream from farming area (S3) (n = 72). Multivariate analyses (PCA and CCA) were used for the data joint analyses. The activities related to tilapia farming in net cages promoted an increase in nutrient concentrations, as well as changes in the phytoplankton community, such as increased Cyanobacteria biomass, as it is hypothesized in this paper. Rhodomonas lacustris Pascher & Ruttner contributed to the highest biovolume along the studied period. However, 1 year after net cage installation, we recorded the highest biovolumes of Microcystis aeruginosa (Kützing) Kützing and Dolichospermum circinalis (Rabenhorst ex Bornet & Flahault) Wacklin, Hoffmann & Komárek. Both species were associated with higher concentration of ammonium and total phosphorus. The hydrodynamic characteristics of the analyzed system, such as short residence time (21.6 days) and outflow (172 m 3 s-1), probably generated the capacity to assimilate disturbances in water quality caused by the employed production process and are therefore instrumental in mitigating the impact of the organic load (from the feed and fish metabolism) in the studied aquatic system.

Influence of environmental variables on the diatom communities of oligotrophic reservoirs for public water supply (Guarulhos, Southeast Brazil)

“…We found a greater diatom biodiversity in the plankton, in contrast to Almeida & Bicudo (2014) who found a greater biodiversity in the surface sediments. In agreement with Rosini et al (2016), who reported changes in the structure of the phytoplankton in an oligotrophic reservoir, we found that the distribution of species in the reservoirs varied according to environmental factors.…”

Detection of Cyanotoxin-Producing Genes in a Eutrophic Reservoir (Billings Reservoir, São Paulo, Brazil)

“…Cyanobacteria and eukaryotic microalgae were identified by their morphometric characteristics. Phytoplankton counts were performed using sedimentation chambers (5 mL) on a Carl Zeiss Inverted Microscope, 400× augmentation, and limit criteria were as established previously by other authors [60,61]. After counting, densities were converted to biovolume (mm 3 /L) using each taxon-specific biovolume from previous publications [62,63].…”

Characterization of phytoplankton by pigment analysis and the detection of toxic cyanobacteria in reservoirs with aquaculture production

“…4). The 2 dominating species in these reservoirs, Cryptomonas brasiliensis and Rhodomonas lacustris, are single cells of a relatively small size, 6 to 10 µm, which have been found to dominate in turbulent and oligotrophic environments of other Brazilian reservoirs (Rosini et al 2016). Furthermore, the most abundant diatom (Fragilaria sp.)…”