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Shore Scene: Shrinkage in Nature’s Sieve

By Jan Sattler and Mia Davidson

5 col shore scene California Mussel B & WCalifornia Mussels (Mytilus californianus) are the most commonly found empty shell and are the most visible mollusks observed along Laguna Beach’s shore.  The bivalves have bluish-black shells and orange colored flesh. They take three years to reach a full size and can live up to 30 years.  Mussels are either male or female and spawn year-round by releasing eggs and sperm into the open water.

Located mostly on the exposed rocks down to about 80 feet, they are usually seen clustered together in the mid to upper-intertidal zone exposed to strong wave action.  Attached to the substrate with byssal threads, protein fibers produced by the mussel, they live in large dense colonies called mussel beds.  Byssal threads have long been studied by scientists for their natural adhesion, elasticity and strength, both for industrial use and human use in the production of artificial ligaments and tendons.

Natural predators include ochre sea stars, crustaceans, birds, some carnivorous sea snails and historically, they were an important food source for coastal Native Americans.  In Southern California today, they are not considered an important fishery.  However they are an ecologically critical part of the coastal environment.  When submerged, they filter two to three quarts of water an hour as they strain their diet of phytoplankton and organic detritus. As filter feeders, they consume and concentrate environmental toxins so are considered a keystone species for monitoring environmental pollution. Also, a myriad of other marine organisms depend on them for food, protection and habitat and any decline would impact a wide range of other species.

In Southern California, studies indicate that mussel populations are declining.  Pollution, climate change and algae blooms may be contributing to this drop, but human impacts including trampling, disturbance and collection for food or bait have also resulted in widespread destruction. For this reason, Laguna Ocean Foundation’s tidewater docents and educators spend much of their time in the tidepools protecting the mussel beds. Laguna Beach is either a state marine reserve or a no-take state marine conservation area, and thus there is absolutely no collecting of mussels for any reason.

 

Laguna Beach residents Jan Sattler and Mia Davidson are year-round ocean swimmers and members of Laguna Ocean Foundation. Find more info at  www.lagunaoceanfoundation.org

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