California Mussels (Mytilus californianus)

Contributed by Dr. Bonnie Becker

Where found:  Form large beds from above the high tide to well below the low water mark. Occurs only where there are crashing waves.

Interesting facts:

• Young mussels are capable of locomotion using their foot, as long as they are not wedged in between other mussels and barnacles. They can pull themselves off their byssal roots, move one foot ahead, and secrete new hairs.
• Mussels have been eaten by humans since before the arrival of Europeans. In the summer, mussels are often avoided due to the accumulation of toxins from the dinoflagellates they eat. California has a ban on mussel collection from May 1 to October 31. At any time of year, if you feel your lips becoming numb while eating mussels, you should seek medical attention immediately.
• These animals are very often found in conjunction with gooseneck barnacles and sea stars. BPT refers to this as the Myttlus-Pollicipes-Pisaster Pisaster is noticeably missing from the Cabrillo National Monument tidepools.

Adaptations:  Mussels are very well adapted for wave-swept coasts. They are anchored to the rocks using byssal hairs, which are secreted by the foot.

Food:  California mussels are filter feeders, straining out phytoplankton and other small particles from the water.

Predators:  Shorebirds, crabs, snails, sea otters, humans, and sea stars (Pisaster). Pisaster is such a voracious mussel eater that they are often the determining factor of the lower limits of mussels. Sometimes young mussels will settle further seaward and escape predation by growing too large to be eaten. Another source of mussel mortality is large storms, which can punch holes in the mussel beds, which are weakened by the damage.

Life history:  Mytilus breeds throughout the year, with peaks in July and December. The sexes are separate. Growth rates are related to water temperature (individuals in warmer water grow faster).

Classification:
Phylum:           Mollusca (Soft-bodied animals with external shells or modified internal shells)
Class:              Bivalvia (Bivalves: Clams, Cockles, Mussels, Oysters, Shipworms, etc.)
Subclass:         Pteriomorpha
Order:             Mytiloida
Family:            Mytilidae

Last revised 11-Jun-13