Carolina Fernández

Effects of chlorpyrifos on the growth and ultrastructure of green algae, Ankistrodesmus gracilis.

The effect of the organophosphorus insecticide chlorpyrifos on the growth, biovolume, and ultrastructure of the green microalga Ankistrodesmus gracilis was evaluated. Concentrations of 9.37, 18.75, 37.5, 75 and 150mgL(-1) of chlorpyrifos were assayed along with a control culture. At the end of the bioassay the ultrastructure of algal cells from control culture and from cultures exposed to 37.5 and 150mgL(-1) was observed under transmission (TEM) and scanning electron microscopy (SEM). After 24 and 48h, treatments with 75 and 150mgL(-1) inhibited the growth of A. gracilis; whereas after 72 and 96h, all the treatments except at 9.37mgL(-1) significantly affected the algae growth. The effective concentration 50 (EC50) after 96h was 22.44mgL(-1) of chlorpyrifos. After the exposure to the insecticide, an increase in the biovolume was observed, with a larger increase in cells exposed to 75 and 150mgL(-1). Radical changes were observed in the ultrastructure of cells exposed to chlorpyrifos. The insecticide affected the cell shape and the distribution of the crests in the wall. At 37.5mgL(-1) electodense bodies were observed along with an increase in the size and number of starch granules. At 150mgL(-1) such bodies occupied almost the whole cytoplasm together with lipids and remains of thylakoids. Autospores formation occurred normally at 37.5mgL(-1) while at 150mgL(-1) karyokinesis occurred, but cell-separation-phase was inhibited. The present study demonstrates that the exposure of phytoplankton to the insecticide chlorpyrifos leads to effects observed at both cellular and population level.

Phytoplankton structure and diversity in the eutrophic-hypereutrophic reservoir Paso de las Piedras, Argentina

This study aimed at analyzing the phytoplankton structure and dynamics in Paso de las Piedras Reservoir, Argentina, through the study of dominant species, diversity and similarity in relation with the abiotic environment. Samples were collected weekly or biweekly (January 2004–June 2005) at four sampling stations. The reservoir experienced a seasonal progression in phytoplankton composition that underlines six successional periods, each one characterized by the dominance of one or a few species. Cyanobacteria, green algae and diatoms were the most important constituents of the reservoir’s phytoplankton. Cyanobacteria dominated during summer and early autumn, green algae during late autumn and early winter, and diatoms during winter and spring. A high abundance of R. lacustris (Cryptophyceae) was observed during late September and early October. The general pattern of species succession is coherent with the general model of plankton seasonal succession described by the PEG model; however, the major discrepancy is the extremely short clear water phase observed. Successional periods were associated with changes in abiotic variables, and they showed differences in ecological traits. Cyanobacteria-Dictyosphaerium, Cyclotella, Stephanodiscus and Anabaena-diatom periods were characterized by a low number of cells, high diversity, with both dominance and specific richness low. On the contrary, during Cyanobacteria and Cyanobacteria II periods, the highest abundance was observed associated with low diversity and high dominance.

Factors Triggering Cyanobacteria Dominance and Succession During Blooms in a Hypereutrophic Drinking Water Supply Reservoir

As freshwater bodies become enriched in nutrients, there is a shift in the phytoplankton community toward dominance by cyanobacteria. Cyanobacterial blooms are a significant problem in water supply reservoirs worldwide because some species can release toxic compounds and are also associated with the production of bad odor and taste. The aims of this paper were to elucidate the mechanism inducing the development of cyanobacterial blooms and to understand the species succession during the bloom, as well as the influence of abiotic factors on the species composition. Total phosphorus level and parameters related to seasonality, i.e., temperature and solar radiation, were the factors triggering the development of the blooms. Blooms were dominated by Microcystis natans and Anabaena circinalis. Phosphorus was an important limiting factor for Anabaena development but never limited Microcystis growth. Water temperature was optimum until end of February for Anabaena, whereas Microcystis growth was slightly limited since water temperature never reached the optimal. Solar radiation was more limiting than temperature, and the decrease in light had a strong role in the bloom decline. Four species of cyanobacteria recorded in Paso de las Piedras reservoir are potentially toxic: Snowella fennica, Microcystis aeruginosa, Planktothrix agardhii, and A. circinalis, being the last one as the most abundant species during the blooms. Considering the Alert Level Framework for cyanobacteria, alert level 2 was exceeded only during blooms while alert level 1 was exceeded during almost all the year.

Intertidal seaweeds from North Atlantic Patagonian coasts, Argentina

Fil: Croce, Maria Emilia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Bahia Blanca. Planta Piloto de Ingenieria Quimica (i); Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Bahia Blanca. Instituto Argentino de Oceanografia (i); Argentina. Universidad Nacional del Sur; Argentina