The blue mussel is a popular shellfish that is harvested from Rhode Island waters.
The blue mussel is a popular shellfish that is harvested from Rhode Island waters.
E. Zabel, courtesy of URI

Blue Mussel (Mytilus edulis)

Alternate common name: Edible Mussel.
Color: Blue black to brown outside, with shiny violet interior.
Size: Up to 4 inches long, 2 inches wide.
Habitat: Intertidal shallow water along the shoreline and throughout the Bay; attached to rocks, pilings, shells, and other solid objects.
Seasonal appearance: All year.


Shaped like a rounded triangle, the blue mussel is a hinged, filter-feeding bivalve found in Rhode Island waters. The blue mussel has a slender, brownish foot that allows it to temporarily hold onto a substrate. A strong, thread-like anchor, called a byssal thread, allows the blue mussel to attach itself securely to almost any substrate. The byssal threads are secreted as a liquid by a gland near the blue mussel's foot, and the threads harden upon contact with water. Byssal threads are tough but not necessarily permanent structures. Instead of a large protruding siphon common to hard-shell clams, the blue mussel has two short siphons on the inside of the shell, which direct the flow of water in and out. The blue mussel is similar to another species, the ribbed mussel.

Life History and Behavior

To find protection or food, the blue mussel moves by releasing the byssal threads and using its foot to move to a new location. Blue mussels feed by filtering detritus and plankton from the water. Cilia inside the blue mussel create a current pulling in water and plankton. Blue mussels live in dense colonies called mussel beds. When the tide comes in, the animal partially opens its shell and takes in water. Blue mussels resist dehydration during low tide by tightly closing their shells. Their major predators are sea stars, whelks, fish, birds, and humans.

The blue mussel is able to withstand great temperature extremes, including freezing, excessive heat, and drought. If a blue mussel is left exposed to air when the tide goes out, it survives by passing air over its moist gills to breathe. Blue mussels prefer areas of high salinity, while ribbed mussels are more prevalent in marshes where the salinity has been diluted by fresh water. Like clams, mussels have growth rings, which show their age, and full maturation takes from one to five years.

Critter Fact Blue mussels play an important role in Rhode Island estuaries as filter feeders, removing bacteria, heavy metals, and toxins from the water column.

Special Notes

Adapted from The Uncommon Guide to Common Life on Narragansett Bay. Save The Bay, 1998.