Humans have used mussels as food for thousands of years and continue to do so. About 17 species are edible, of which the most commonly eaten are Mytilus edulis, M. galloprovincialis, M. trossellus and Perna canaliculus. Although mussels are valued as food, mussel poisoning due to toxic planktonic organisms can be a danger along some coastlines. 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 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.