California Musssel Shell, Mytilus californianus
California Mussel Shells, Mytilus californianus. Shell collected off the beaches of Southern California, May 2014. Size: 10.9 cm (4.3 inches) x 6.5 cm (2.6 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.
Phylogeny: The California Mussel, Mytilus californianus (Conrad, 1837), is a is a bivalve mollusk that is a member of the Mytilidae Family of Mussels. The genus Mytilus is one of thirty-two genera in this family, and there are eight species in this genus. This species is also known as the Ribbed Mussel.
Description: The California Mussel Shell is large and elongated, with a straight anterior margin and a curved posterior margin. The beak is sharply pointed. They have prominent radial ridges on the basal portion of the shell. Mature shells have a bluish-black color; the juveniles can have brown or white streaks. The interior of the shell is blue-grey with an iridescent sheen. The foot of the living animal is orange. California Mussel Shells reach a maximum length of 25 cm (9.8 inches) and 14 cm (5.4 inches) in height.
Habitat and Distribution: California Mussels attach themselves, by use of byssal threads, to surf washed rocks, pier pilings and other hard substrates. They live intertidally, and to depths up to 24 m ( 79 feet), though some sources extend the maximum depth to 90 m (295 feet). They are a temperate to tropical Eastern Pacific species. In Mexican waters they are found along the entire west coast of the Baja Peninsula, though they are most common north of Magdalena Bay, Baja California Sur. They are also found around Socorro Island.
Ecology and Behavior: California Mussels are suspension feeders that feed primarily on phytoplankton and fine detritus. They are prey for fish, crabs, shore birds, gastropods, and sea stars, such as the Ochre Starfish, Pisaster ochraceous. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. They spawn all year, with spawning peaking in July and December. California Mussels are known to host several endoparasitic species including isopods, the pea crab Fabia subquadrata, and the pycnogonid Achelia chelata.
The presence of California Mussels is a good indicator of water quality as they require clean water for survival. California Mussels are edible and have been used for thousands of years by local indigenous people as a food source. During Summer months, plankton blooms , especially of the dinoflagellate Gonyaulax catanella, can cause mussels to become toxic leading to paralytic shellfish poisoning. From a conservation perspective they have not been formally evaluated however they are one of the most abundant macro invertebrates found along rocky habitats, they have a relatively wide distribution, and should be consider to be of Least Concern.
Synonyms: Mytilus californicus, Mytilus canalis, Mytilus edulis giganteus, and Mytilus zonarius.