The 18th of January 2022 high concentrations of“paralytic shellfish poisoning” toxin were detected.in mussels Although these events are scarce, they entail serious health risks. Previous events of this toxin were registered in December 2018, and October 2018. To track the posible origins of the phytoplancton producing this toxin, we analysed the environmental conditions affecting the área during the 10 days preceding this peak and various backward-in-time simulations of particles drift were run with local coastal models. As a result we saw that 4 days before the peak the origins found were located locally near the coastline and at the Ondarroa’s port. However for periods older that 5 days, the likely origins were found in western offshore áreas. These backward-in-time simulations have helped us to discard some origin hypothesis and refine others, and have proven a very useful element to progress in our knowledge of HABs origins and evolution, and their potential impact on the Mendexa’s mussels production area.

Work co-funded by AVACON, BIOTOX ( Gobierno vasco. Dirección de Pesca y Acuicultura ) and PRIMROSE European Commission Espacio Atlántico Operativo 2007 2013