California Mussel (Mytilus californianus)

Description: The California mussel is one of the most abundantly found mollusks along the Oregon Coast, especially at Haystack Rock. On the outside, the oblong shells of California mussels are usually blue-black and sometimes have brown sections. The inside of the shell is a blue-gray color with iridescent patches, and the actual meat of the mussel inside the shell is bright orange. This species is most easily identified by having radiating ribs lengthwise on the shell. It’s possible to find baby California mussels along Oregon’s coastline that are only a few millimeters long, but these shellfish also reach lengths of up to 25 cm. At the more pointed base of the shell, mussels secrete a thick fiber called byssal threads that attach themselves to hard surfaces like rocks or other mussels.

Habitat: At Haystack Rock, California mussels are found covering the top halves of boulders in very dense groups. California mussels are found along North America’s Pacific Coast from Alaska to Baja California, Mexico. 

Diet: When the tide comes in and the ocean covers the boulders that the mussels reside on, the mussels filter feed to capture plankton or other particles in the water column.

Tide Pool Tidbits:

• A single mussel can filter up to 3 liters of water in just one hour!

• Many other tide pool critters can be found living in the crevices of mussel beds or even on top of mussels, especially arthropods like barnacles and crabs, or other mollusks like limpets and chitons.

• One female California mussel can produce 100,000 eggs in a year.

• Individuals living in deeper waters (lower intertidal) tend to grow faster and bigger thanks to having more consistent access to food and less exposure. How low on a rock these mussels live is often determined by how fast sea stars eat them!

References: Animal Diversity Web, The New Beachcomber’s Guide to the Pacific Northwest by J Duane Sept