Univ Rennes, CNRS, ECOBIO - UMR 6553, F-35000 Rennes, France.
IFREMER/Phycotoxins Laboratory (PHYC), F44311 Nantes, France.
Harmful Algae. 2019 Jul;87:101639. doi: 10.1016/j.hal.2019.101639. Epub 2019 Jul 12.
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 × 10 cells mL) at the freshwater sites during the summer and autumn periods of both years, with a cell transfer to estuarine (up to 10 cells mL) and marine (2 × 10 cells mL) 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, and more intermittently with concentrations up to 1.15 μg L, 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 and <0.03 μg L). 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.
淡水水体中蓝藻的增殖频率在全球范围内不断增加，而相关的蓝藻毒素的存在对生态系统和人类健康构成了威胁。虽然微囊藻（MC）的存在——最广泛的蓝藻毒素，在淡水中已有充分的记录，但仅有少数研究考察了其在河口水中的存在情况。在这项研究中，我们评估了从法国布列塔尼的一个淡水水库通过一个相连的河口到沿海地区的河流连续体中蓝藻和蓝藻毒素的迁移情况。我们在 2 年内定期在 5 个站点沿河流连续体采样，并分析了浮游植物和蓝藻毒素，以及理化参数。结果表明，蓝藻在浮游植物群落中占主导地位，在两年的夏季和秋季，淡水点的密度很高（高达 2×10 个细胞 mL），并向河口（高达 10 个细胞 mL）和海洋（2×10 个细胞 mL）点转移。蓝藻密度的时间变化主要与温度有关，而空间变化则与盐度有关，同时营养物质对蓝藻的生长没有限制。蓝藻生物量主要由几种能够在中等盐度下存活的微囊藻物种组成。在所有的淡水样本中都检测到了细胞内 MC，浓度高达 60μg L，而在最上游的河口站点，浓度更间歇性地达到 1.15μg L。细胞内 MC 仅在最下游的河口点和海洋出口处偶有检测到，浓度分别低于 0.14μg L 和 0.03μg L。检测到了不同的 MC 变体，以 MC-LR、RR 和 YR 为主导，这种主导地位沿着盐度梯度保持不变。在下游站点，细胞溶解导致细胞外 MC 对总 MC 的贡献更高。在颗粒样品或滤液中均未检测到节球藻毒素（NOD）。
