Demonstrated transfer of cyanobacteria and cyanotoxins along a freshwater-marine continuum in France

Type Article
Date 2019-07
Language English
Author(s) Bormans Myriam1, Amzil ZouherORCID2, Mineaud Emilien1, Brient Luc1, Savar Veronique2, Robert Elise2, Lance Emilie3, 4
Affiliation(s) 1 : Univ Rennes, CNRS, ECOBIO – UMR 6553, F-35000 Rennes, France
2 : IFREMER/Phycotoxins Laboratory (PHYC), F44311 Nantes, France
3 : UMR-I 02 SEBIO, Campus du Moulin de la Housse, BP 1039, 51687 REIMS Cedex 2, France
4 : UMR 7245 MNHN/CNRS Molécules de Communication et Adaptation des Microorganismes, 12 rue Buffon, F-75231, Paris, France
Source Harmful Algae (1568-9883) (Elsevier BV), 2019-07 , Vol. 87 , P. 101639 (11p.)
DOI 10.1016/j.hal.2019.101639
WOS© Times Cited 36
Keyword(s) Cyanobacteria, Intracellular and extracellular microcystins, Estuary, Salinity

The frequency of cyanobacterial proliferations in fresh waters is increasing worldwide and the presence of associated cyanotoxins represent a threat for ecosystems and human health. While the occurrence of microcystin (MC), the most widespread cyanotoxin, is well documented in freshwaters, only few studies have examined its occurrence in estuarine waters. In this study we evaluated the transfer of cyanobacteria and cyanotoxins along a river continuum from a freshwater reservoir through an interconnecting estuary to the coastal area in Brittany, France. We sampled regularly over 2 years at 5 stations along the river continuum and analysed for phytoplankton and cyanotoxins, together with physico-chemical parameters. Results show that cyanobacteria dominated the phytoplanktonic community with high densities (up to 2 × 106 cells mL−1) at the freshwater sites during the summer and autumn periods of both years, with a cell transfer to estuarine (up to 105 cells mL−1) and marine (2 × 103 cells mL−1) sites. While the temporal variation in cyanobacterial densities was mainly associated with temperature, spatial variation was due to salinity while nutrients were non-limiting for cyanobacterial growth. Cyanobacterial biomass was dominated by several species of Microcystis that survived intermediate salinities. Intracellular MCs were detected in all the freshwater samples with concentrations up to 60 μg L−1, and more intermittently with concentrations up to 1.15 μg L−1, at the most upstream estuarine site. Intracellular MC was only sporadically detected and in low concentration at the most downstream estuarine site and at the marine outlet (respectively <0.14 μg L-1 and <0.03 μg L−1). Different MC variants were detected with dominance of MC-LR, RR and YR and that dominance was conserved along the salinity gradient. Extracellular MC contribution to total MC was higher at the downstream sites in accordance with the lysing of the cells at elevated salinities. No nodularin (NOD) was detected in the particulate samples or in the filtrates.

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