Marine biotoxins, also known as phycotoxins, are toxic substances produced by certain species of microalgae (also called harmful phytoplankton). When absorbed by shellfish, they can cause acute intoxications in shellfish consumers, causing symptoms of varying severity depending on the nature of the toxin, the ingested dose and the sensitivity of the individual person. In most cases, these symptoms are reversible.
Bivalve shellfish are a category of molluscs with a double shell that can open and close. All bivalves are aquatic. Most live in seawater, either in sediment, such as the cockle, the clam, the scallop, the wedge clam and the razor shell clam (these are referred to as burrowing shellfish), or fixed to the rocks, like the mussel or the oyster (these are called non-burrowing shellfish).