Natural Life of the Lost Coast: Native freshwater mussels in our local rivers

By David Fuller

Chances are you have heard about non-native, invasive mussels such as the zebra mussel and the quagga mussel. Invasive freshwater mussels have arrived in California and have been spread unintentionally by humans into rivers and reservoirs. Fortunately, these invaders have not yet made it to the North Coast.

Did you know that not all freshwater mussels are invaders? Our local rivers are home to native mussels. These animals quietly sit in groups, partially buried at the bottoms of our local rivers, filtering water, and go unnoticed by most people. Despite their low-key existence, they play an important part in our aquatic ecosystems and are indicators of the health of the rivers.

One of the longest living animals on earth, the Western Pearlshell Mussel is known to live for over 100 years. Western Pearlshell Mussels can be found in the pools of our local rivers. Much like salmon, these mussels need clean, cold water to survive. In fact, Western Pearlshell Mussels depend on salmon. The mussel larvae, called glochidia, hook onto the gills of migrating salmon and are transported upstream before they release from the fish and burrow into the stream bottom where they stay until they reach adulthood. These mussels are elongated in shape, dark brown to black in color, and a few inches in length. Except for the ride they take on a salmon, these animals stay in the same location for their entire, very long, lives.

The California floater mussel lives only 10 to 15 years but can be found in the same local rivers as the western pearlshell. There are several species of floaters in the western U.S. and it is difficult to tell one species from another. California floaters are similar in length to pearlshells but have rounder shells, and vary in color from brown, to reddish brown, to black. These mussels are more general in their habitat requirements as well as the species of fish that the larvae use for transport.

Freshwater mussels are filter feeders -- meaning they sift algae and plankton from the water -- which clean the water and make nutrients more easily available to other animals. A recent study found that lamprey in the South Fork Eel River grew faster in areas near mussel beds because of the nutrients provided by mussels. Mussels are an important source of food for several bird and mammal species in our region.

How can folks tell the difference between the native mussels and the invasive mussels? The invasive zebra mussels and quagga mussels are much smaller. Zebra mussels are striped and grow to the size of a penny while quagga mussels are typically the size of a fingernail. In contrast, our native mussels can reach 5 inches in length. Invasive mussels can damage human infrastructure and alter native ecosystems. To learn more about invasive mussels and see how you can help prevent them from coming to the North Coast see:

David Fuller is a resident of Eureka and the planning and environmental coordinator for the Bureau of Land Management, Arcata Field Office.

This article is part of a series about Natural Life of the Lost Coast, a project of the Lost Coast Interpretive Association. If you are interested in contributing an article to this bi-weekly column about the plants, animals and human history of the Lost Coast Region, contact Cathy Miller at

photo caption:

The Western Pearlshell Mussel