Blue Mussel (Mytilus trossulus)

Description: Blue mussels, or Pacific blue mussels, are a small species of mussel, typically less than 7 cm long but can reach up to 13 cm. They are usually a dark blue or black color (brown individuals are also found, rarely) and can look like young California mussels. One way to differentiate the two species is to look at the texture of their shells - blue mussels have a relatively smooth surface while their larger relatives have vertical groves extending from the base of each shell.

Habitat: Blue mussels range from Alaska to central California. They attach to substrate like rocks or docks in the intertidal zone. At Haystack Rock, blue mussels live within the California mussel beds on large boulders in the mid intertidal zone.

Diet: As filter feeders, blue mussels pump water through their body so that they can capture plankton and other particles in the water column.

Tide Pool Tidbits:

• California mussels and blue mussels packed closely together create a “bed” that functions as a habitat for many other species of plant and animal.

• Mussels are an important food source for ochre sea stars.

• Despite their smaller size, blue mussels can still filter water at the same rate as the larger California mussels - 3 liters per hour!

References: Walla Walla University, The New Beachcomber’s Guide to the Pacific Northwest by J Duane Sept