Assorted barnacles growing on large mussels

Mussels and Clams

Adult mussels
Mussel bed. Notice upper limit and lower limit where mussels live Mussels live in a similar niche as Gooseneck Barnacles Mussels covered with buckshot barnacles Mussels attached to rocks. Notice upper and lower boundary Adult and juvenile mussels Vast mussels beds Ochre sea stars feeding on mussels. They are the reason for the lower limit

California Mussel (Mytilus californianus )

This mussel is the most common mussel found in the intertidal zone. They are typically a few inches in length. The deeper and more exposed the location, the larger the mussels can grow. These mussels usually are dark blue and frequently have other animals attached to their shells. The smaller acorn barnacles are commonly found attached to these mussels. This mussel also lives in groups as the larvae when settling will favor locations where mussels currently exist.

Bay Mussel (Mytilus galloprovincialis )

Bay mussels are similar to California mussels in that they appear darker in color. They are usually smaller in size and live lower in the intertidal areas. Bay mussels prefer areas with less wave action than the larger California mussels. Bay mussels also tend to move around a bit more after settling.
Jewel box clam with closed shell. The top part is usually covered with algae and hard to see
Jewel box clam shell. No longer living Shell of Jewel Box Clam Shell of Jewel Box Clam Shell of Jewel Box Clam

Jewel Box Clam (Pseudochama exogyra )

This clam is also called the Reversed Chama in some publications. This species prefers to live in the lower intertidal zone with lots of expose to moving water. The shells are frequently covered by algae and other animals. This covering makes for a very good camouflage and difficult for the tidepool visitor to find. Most people see this animal after it has died and the shell is open.
Feeding – Mussels and clams have a very unique way of feeding. They essentially pump water from one opening pass the water through their bodies and out another opening. As the water is moving through the body cavity, the water passes over gills that provide oxygen. The water also passes over specialized feeding structures that trap small particles of food. The food is then moved to the mouth area and consumed.

Protection – Mussels and clams use their hard shell for protection. The shell is used for protection from animals and predation but also from drying out when exposed to air. The shell also protects those animals from high wave actions that will crush most other marine life. The shell protects mussels and clams from most but not all predators. Sea stars have adapted to prey on mussels and clams and only the largest mussels and clams can withstand and attack from a hungry sea star.

Ecology - These mussels and clams spend sometimes half the day exposed to air. During this period, the animals will close their shells very tightly making a water proof seal. The mussels and clams will actually use the oxygen in the water in the body cavity to continue breathing for several hours. Mussels and clams can open their shell slightly as needed when exposed to air to allow new air to mix with the water in their body cavity.

Mussels and clams have a multi part life cycle. Adults will cast out sperm and eggs based on specific environmental queues like water temperature, lunar cycle, tide level and many other factors. Once the eggs are fertilized, they morph into a larval stage. The larval stage stays in the ocean for several weeks and then settles on a hard substrate. This decision on where to settle is a very important decision in that they cannot move to far from where they initially settled. Mussel larvae will decide on a location based on a variety of environment queues like water temp, chemical balances and proximity to other mussels. Mussels can actually move around a bit once settled. They have strong byssal threads they use to attach to rocks. These Byssal threads can be detached and new ones produced that the mussel can use to very slowly change location.
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