The almost globally distributed, marine dinoflagellate genera Azadinium and Amphidoma (Amphidomataceae) produce a variety of lipophilic phycotoxins known as Azaspiracids (AZA). These toxins are accumulated mostly by filter-feeders like the blue mussel (Mytilus edulis) and may lead to the azaspiracid-shellfish-poisoning (AZP) syndrome in humans after consumption of contaminated seafood. With respect to the impacts on humans health, AZA-concentrations above the EU-regulatory limit (0.16 mg AZA Kg-1 mussel flesh) go along with closures of shellfish farms and are therefore a threat to the aquaculture industry, as well. Thus, there is a need for a rapid, sensitive and reliable detection and quantification of these microalgae and their toxigenic products. However, this is challenging, as the small-sized cells (12-16 µm) are hardly possible to be identified by traditional light microscopy. Even more challenging, only a few amphidomatacean species produce toxins, and toxigenic and non-toxigenic species can co-occur in the same area. In 2018, a seagoing expedition took place in the North Sea, the English Channel and Irish coastal waters, combining onboard light microscopy, quantitative real-time PCR (qPCR) and liquid-chromatography, coupled with tandem mass-spectrometry (LC-MS/MS), to search for the three azaspiracid-producing species known from the North Atlantic: Azadinium spinosum, Az. poporum and Amphidoma languida. Findings revealed that AZA-producers and respective toxins were widely distributed in the survey area, with high cell densities in the North Sea area and along the Irish coastline. Highlight was a bloom stage of Am. languida with 1.2 × 105 cells L-1, observed on a central North Sea station. Results of microscopy, molecular and chemical analyses matched well, which increased the confidence about species and toxin detection. This study supports again the recommendation to include toxigenic Amphidomataceans into regular monitoring programs and further demonstrated the advantage of real-time, multi-method approaches to investigate inconspicuous, harmful microalgae species in the field.