 For instance, mussels should be avoided along the west coast of the United States during the warmer months.This poisoning is usually due to a bloom of dinoflagellates (red tides), which contain toxins.The dinoflagellates and their toxin are harmless to mussels, even when concentrated by the mussel's filter feeding, but if the mussels are consumed by humans, the concentrated toxins cause serious illness, such as paralytic shellfish poisoning.