Toxicity of Aphanizomenon ovalisporum (Cyanobacteria) in a Spanish water reservoir

The summer phytoplankton population in the Arcos reservoir (Spain), an oligotrophic/mesotrophic waterbody, was dominated by the cyanobacterium Aphanizomenon ovalisporum, accompanied by Planktothrix cf. agardhii and smaller proportions of other cyanobacterial species. The bloom remained for approximately 1 month in the summer of 2004. The Arcos reservoir had moderate conductivity, up to 1756 μS cm^-1, and relatively high nutrient concentrations. Planktonic biomass collected during the bloom period was found to be toxic by the Artemia salina bioassay. Analytical procedures based on high-performance liquid chromatography (HPLC) indicated the absence of microcystins and anatoxin-a but clearly demonstrated the presence of cylindrospermopsin (CYN), suggesting that CYN from Aphanizomenon ovalisporum was the compound responsible for the toxicity in the bioassay. Measurements indicate that up to 9.4 μg CYN1^-1 were present in the sestonic fraction. This is the first report of high concentrations of this cyanotoxin in European waters and the first known instance of a massive bloom of the cyanobacterium Aphanizomenon ovalisporum in Spain.