Adult copepods of Acartia tonsa were fed with Alexandrium pseudogonyaulax producing goniodomin A (GDA) for a week and the intracellular GDA content of A. tonsa was determined. Then, the diet was switched to non-toxic Rhodomonas salina and subsequently the reduction in GDA content within A. tonsa over an eight-day period was assessed. The preparation and execution of the experiments were carried out between May 1 and July 15, 2022 in the laboratories of the Alfred-Wegener-Institute, Helgoland, Germany.