Seasonal Occurrence of Cyanobacteria and First Detection of Microcystin-LR in Water Column of Foum-Gleita Reservoir, Mauritania

Abstract

This work was carried out to study the seasonal occurrence of cyanobacteria and their microcystin-LR in water column of Foum-Gleita reservoir (Mauritania). Limnological and biological factors were investigated at three depths (surface, -3, and -6 m) in this reservoir during a full year. Nutrients were analyzed by Spectrophotometry, phytoplankton was analyzed by Inverted Microscopy, microsystins were analyzed by High Performance Liquid Chromatography-tandem Mass Spectrometry and environmental factors relationships were analyzed by Pearson's correlation and Multiple Linear Regression. Physicochemical analyzes have shown that this reservoir is hypereutrophic with dissolved inorganic nitrogen and total phosphorus concentrations relatively high, varying from 1.39 to 6.53 and 0.21 to 0.57 mg/L, respectively. Annual surface water temperature was exceptionally high (27.8 ± 3.6°C), characterizing of a Sahelian climatic conditions. Phytoplankton analyzes have shown dominance of two toxic cyanobacteria species Microcystis aeruginosa and Dolichospermum os-aquae during warm season (May-September). Microcystins analysis revealed presence of only most toxic variant, microcystin-LR. Microcystin-LR concentration in the surface water samples, during cyanobacterial blooms, was consistently high (5.638 µg/L), exceeding 5-times the World Health Organization drinking water limit (1 µg/L), however, it was much lower (0.83 µg / L) at depth (-6 m). Analysis of environmental factors relationships showed that the most in uential factors on abundance of Microcystis aeruginosa and Dolichospermum os-aquae and variability of microcystin-LR concentrations were total phosphorus, dissolved inorganic nitrogen, iron, temperature and pH. Finally, the study clearly demonstrated need for regular monitoring of cyanobacteria and cyanotoxins in the waters of studied reservoir.

The “Bald Disease” of the Sea Urchin Paracentrotus lividus: Pathogenicity, Molecular Identification of the Causative Agent and Therapeutic Approach

“…Previous findings could indicate a multi-factorial origin of the disease, influenced by a peculiar coincidence of physiological conditions (sea urchins are at the end of their reproductive season), environmental conditions (seasonal changes of temperatures, storms, planktonic microorganism blooms) and food web cycles (the re-start of algal growth, increase in daily irradiation; [ 31 ]). However, it is also known that some microorganisms, such as cyanobacteria, are subject to seasonal cycles of abundance [ 34 ]. For example, Almanza et al [ 35 ] observed that the trophic state of water bodies, according to seasonal cyclical rhythms, deeply influences the frequency and the distribution of cyanobacterial blooms.…”