微小辐环藻, 我国硅藻藻华的新记录种

2016年5月4日—10日, 海南省海口市红城湖发生了一起硅藻藻华。为明确该起藻华的肇事生物, 于藻华期间采集了水体样品, 经过光镜和电镜下的形态学观察, 确认藻华原因种为微小辐环藻Actinocyclus exiguus Fryxell & Semina, 该种是我国硅藻的新记录种, 其藻华在我国也是首次报道。微小辐环藻隶属于中心纲硅藻, 细胞单独生活或形成胶质状群体, 细胞个体较小, 壳面直径为6.4~11.1μm, 有2个或3个壳缘唇形突, 壳缘处具有眼斑结构。水体中丰富的氨氮(平均值为2880μg?L^-1)和较高的水温(31℃)条件可能是藻华事件的环境诱因。藻华事件导致红城湖40余吨花鰶死亡。经过鱼体检测, 初步排除因为藻毒素、鱼鳃机械性损伤或水体缺氧而致死的可能, 水体盐度剧烈变化等物理应激反应导致鱼类死亡的可能性较大。

Actinocyclus exiguus,a newly discovered diatom bloom-causative species in China

To clarify the causative species of a diatom bloom occurred in Hongcheng Lake of Haikou City, Hainan Province during 4-10 May 2016, several water samples were collected from bloom regions. Based on the morphological features under light and electron microscopy, the causative species was identified as Actinocyclus exiguus Fryxell & Semina, a newly recorded diatom species in China. Its bloom was also new in China, and was the second case globally. Actinocyclus exiguus belongs to centricae diatom, and their cells are usually solitary, or sometimes form colonies in mucilage. The cells are small in size, with diameter around 6.4~11.1 µm. There are 2~3 rimoportulae at valve margin, as well as a pseudonodulus. It is speculated that rich density of ammonia-nitrogen (average of 2880 µg?L^-1) and high water temperature (average of 31℃) could be important induced factors for this A. exiguus bloom. About 40 tons of dead fishes (Clupanodon thrissa) was reported during the bloom; and algal toxins, mechanical injury and dissolved oxygen in the water were excluded as the mortal factors, after body check of dead fishes. Physical stress reactions, such as acute change of salinity, might be responsible for the death of the fishes.