Mussels (Mytilus) are relatives of clams and are commonly found in the middle to lower rocky zones attached to rocks by strong threads which the animals secrete. Blue-black in color, mussels are filter feeds. They feed by passing sea water over a filtering structure (the gill) which removes organic particles and small organisms like plankton and pass them on to the mouth.
While in many areas mussels are a popular food source for people, one must use caution with the mussels of Bartlett Cove. They are edible during parts of the year, but in the summer and fall they may become poisonous. One of the tiny organisms that blooms in the plankton is a dinoflagellate (Gonyaulax) which secretes a potent toxin. The toxin does not affect the mussels, but they accumulate it and may store it for a month or more. A single heavily tainted mussel is sufficient to kill a person. This syndrome, paralytic shellfish poisoning, is a serious danger over most of the Pacific Coast and mussels and other filter feeding clams should be eaten with due care during summer. Mussel beds provide a home for many other organisms which live in the protected spaces between mussels. Mussel beds can become so thick that they overgrow other sessile animals like barnacles.