Pick Our Brain - April 2010

What are a California floater and a western pearshell?

The California floater (Anodonta californiensis) and the western pearshell (Margaritifera falcate) are two of several species of freshwater mussels native to California. In addition to the Anodonta species and the western pearshell, the western ridged mussel (Gonidea angulata) is also found in California. Although these native mussels are currently uncommon, a recent search by Jeannette Howard of The Nature Conservancy found them in about half of the California locations where they were reported historically. Often looking like stones or buried in bottom sediments, they are easily overlooked, but these fascinating native organisms have been here for thousands of years.

Interest in native mussels has been renewed recently because the Environmental Protection Agency has proposed new ammonia criteria that are contingent on the presence or absence of native freshwater mussels.

Interesting Facts About Freshwater Mussels

  • Freshwater mussels are sensitive to environmental change and are considered one of the most endangered groups of freshwater organisms in North America.
  • With about 300 native species, the freshwater mussels reach their greatest worldwide diversity in North America.
  • Freshwater mussel larvae are parasitic, attaching to fish for a time during their early life history.
  • Many species of freshwater mussels have developed elaborate lures to attract fish to be hosts for their larvae.
  • Many species of fish are host to mussel larvae including trout and salmon, but they do not appear to cause any significant harm to the host fish.
  • Some freshwater mussels can live to be 100 years old. Specimens of one of our native California species, Margaritifera falcata, have been found that were 80 years old.
  • In the central and southern United States, freshwater mussels were once harvested in great numbers to manufacture buttons from their shells.

Freshwater mussels are a little-known component of California streams and rivers. The recent documentation of their widespread presence in our freshwater ecosystems is an important finding since these mussels are important indicators of water quality.