Currently four Alexandrium species are known to produce goniodomins (GD): A. hiranoi, A. monilatum, A. pseudogonyaulax and A. taylorii. Whereas A. hiranoi seems to be constrained to the Northwestern Pacific and A. monilatum to the Americas, records of A. pseudogonyaulax and A. taylorii suggest a more global distribution. To date only goniodomins A (GDA) and B (GDB) haven been described. Analysis of GD profiles of the four species revealed that GDA was the most abundant variant in cell extracts of most strains, but several other GD variants were present in all strains. However, one A. taylorii strain originally isolated from Japanese coastal waters produced the putative 34-desmethyl-GDA as the primary compound in the GD group. The observation that extracellular GD profiles differed completely from those obtained by cell extraction prompted stability testing of GDA, which showed rapid conversion of GDA into different variants. Monitoring data and field data of surveys performed in 2016 and 2020 on the Eastern North Sea, Danish Limfjord and the Western Baltic Sea indicate an expansion of A. pseudogonyaulax in Northern European waters. This is of particular concern as A. pseudogonyaulax and the other three species are suspected to be ichthyotoxic. This is in agreement with the fact that extracellular compounds of all four species cause cell lysis of co-occurring protistan species. However, extracellular GD did not significantly contribute to protistan cell lysis and thus other bioactive extracellular compounds (BEC) must be involved in this effect.