California Mussel

Mussels attach themselves to rocks very tightly. From time to time they sneak their foot (the part inside the shell) out and touch the rocks, secreting a special thread of cement. After doing this several times, these threads of cement hold the mussel to the rock, sometimes permanently.

Once a mussel has found a home, it opens little valves on its sides slightly to let in seawater and food particles. Much like a fish, it filters the food from the water by using its gills. Mussels like to eat mostly fine organic material and plankton. When a large group of mussels get together (around 1 million mussels) they can take in about 35 tons of food in a year!

Colonies of mussels are often hurt badly by big waves on the open coast. Starfish eat mussels and pry some of them off the rocks. Holes in the colonies can cause the waves to break even more of them off the rocks - much like soil erosion when trees are cut down. A rock face that has been completely cleared of mussels takes about 2.5 years to be repopulated. So when you find a mussel, it's a good idea to leave it on the rock.