Fine‐scale spatial variability in anatoxin‐a and homoanatoxin‐a concentrations in benthic cyanobacterial mats: implication for monitoring and management

Aims: The purpose of this study was to determine the variability in anatoxin‐a (ATX) and homoanatoxin‐a (HTX) concentrations in benthic cyanobacterial mats within sampling sites and to assess the applicability of using a PCR‐based approach to determine ATX‐ and HTX‐production potential. Methods and Results: ATX and HTX variability was investigated by collecting 15 samples from 10 × 10 m grids in seven rivers. ATX and HTX concentrations were determined using liquid chromatography-mass spectrometry (LC-MS). Samples from two sites contained no ATX or HTX and at one site ATX and HTX were detected in all samples. At four sites, both toxic and nontoxic samples co‐occurred and these samples were sometimes spaced less than 1 m apart. PCR amplification of a region of a polyketide synthase (ks2, putatively involved in the biosynthetic pathway of ATX and HTX) successfully distinguished ATX‐and‐HTX‐ and non‐ATX‐and‐HTX‐producing cultured Phormidium strains. Results from environmental samples were more variable, and the results were in congruence with the LC-MS data in only 58% of samples. Conclusions: Fine‐scale spatial variability in ATX and HTX concentrations occurs among benthic cyanobacterial mats. Significance and Impact of the Study: Multiple benthic cyanobacterial mat samples must be collected at a sampling site to provide an accurate assessment of ATX and HTX concentrations at that location. The PCR‐based technique offers the potential to be a useful early warning technique.