California mussel
The big blue-black mussel that packs Pacific rocks by the thousands, anchored by threads so strong they inspired medical glue.
California mussel at a glance
Mytilus californianus Mytilus californianus is MY-till-us kal-ih-forn-ee-AH-nus
- Type
- Invertebrate · mussel
- Diet
- Other
- Size
- Usually about the length of your palm, up to roughly 8 inches, one of the largest mussels on the coast.
- Lifespan
- Often 20 to 30 years, and some live far longer.
- Conservation
- Not formally assessed by IUCN; common along the Pacific coast
Eats plankton, tiny bits of drifting food
It filters seawater. Water is drawn in through the shell, tiny drifting plankton and food particles are strained out and eaten, and the clean water is pushed back out. A single mussel can filter several gallons a day.
Should you worry?
Harmless to touch, but the shells are sharp and the rocks they cover are slick, so tide-pool footing is the real hazard. Never eat wild mussels you find, especially in summer, when they can carry a natural poison from red-tide algae.
A mussel bed looks like the simplest thing on the shore, a black patch of shells so crowded you cannot see the rock beneath them. It is actually one of the busiest addresses on the coast. Down in the gaps between the packed shells, out of the waves and the sun, live worms, crabs, tiny snails, and creatures barely visible, hundreds of animals sheltering in a single patch. The mussels build the neighborhood, and everything else moves into the spaces between.
What keeps the whole block from washing away is a trick worth stealing. Each mussel spins a bundle of tough, stretchy fibers called byssal threads and cements them to the rock, and the glue on the end of each thread sets hard even underwater, in salt, in pounding surf. That is a thing human glue cannot do, and scientists have spent years studying mussel cement to invent adhesives that can close a wound or stick to a wet bone. The animal solved the problem first.
Watch a bed as the tide drops and the shells all clamp shut with a faint hiss of trapped water, thousands of them sealing at once to wait out the dry hours. Come back as the sea climbs the rock and they open again to feed, each one straining gallons of water for the drifting specks it eats. The footing is slick and the shells are sharp, so step around a mussel bed rather than on it, and let the crowded little city do its work.
Did you know?
- It anchors to rock with a bundle of tough stretchy fibers called byssal threads, and the glue on those threads sticks even underwater, which is why scientists have studied it to make better surgical adhesives.
- A mussel bed is a whole neighborhood. Worms, crabs, snails, and tiny creatures live packed in the spaces between the shells, so a single patch of mussels can shelter hundreds of other animals.
- It can clamp its shell shut and survive for hours out of water when the tide drops, then reopen to feed when the sea returns.
Common questions
How does a mussel hold onto the rock?
It spins a bundle of tough fibers called byssal threads and glues them down. The glue works even underwater, which is so useful that scientists have studied it to invent better medical glues.
What lives in a mussel bed?
Hundreds of other animals. The gaps between packed mussel shells shelter worms, crabs, snails, and tiny creatures, so a mussel bed is really a crowded apartment block for the whole shore.
Can you eat mussels from the beach?
Not safely on your own. Wild mussels, especially in warm months, can build up a natural poison from red-tide algae. Only mussels tested and sold for food are safe to eat.