A comparison between the FlowCam 8100, microscopy, and sandwich hybridization assay for quantifying abundances of the saxitoxin-producing dinoflagellate, Alexandrium catenella

•Microscopy, FlowCam, SHA return non-significantly different Alexandrium abundances.•The FlowCam distinguished Alexandrium from other genera in field assemblages.•Data integration from all three approaches has potential to enhance HAB monitoring. Light microscopy, FlowCam, and sandwich hybridization assay (SHA) are three approaches that facilitate the monitoring of harmful algal bloom (HAB) forming phytoplankton. Yet, cross-comparisons among these techniques have not been conducted. This study addressed that gap using the saxitoxin-producing ‘red tide’ dinoflagellate Alexandrium catenella, a species responsible for blooms and paralytic shellfish poisoning worldwide. To achieve this goal, the dynamic ranges of each technique were compared using A. catenella cultures spanning low (pre-bloom), moderate (bloom), and high (dense bloom) levels. To assess field detection, water samples containing very low ( 0.05). However, relative to microscopy at times SHA produced non-detect signals 0.05 for all treatments). Findings are relevant to HAB researchers, managers, and public health officials because they help reconcile disparate cell abundance datasets that inform numerical models and enhance HAB monitoring and prediction. Results are also likely broadly applicable to several HAB species.