In December, biologists from the Sacramento Fish and Wildlife Office (SFWO) visited San Francisco Public Utilities Commission's (SFPUC) watershed property on the San Francisco Peninsula in search of freshwater mussels. Buried in the sediment of chilly creeks, freshwater mussels can be difficult to spot for the untrained eye.
“I didn’t realize how many mussels we were about to find,” said Lauren Kong, a biologist in SFWO's Recovery and Conservation Planning Division with expertise in freshwater mussels. “We found a couple hundred western pearlshell mussels across several streams and dense mussel beds.”
As filter feeders, freshwater mussels play an important role in water health, cleaning it of organic material, bacteria and plankton just as their marine counterparts do. They’re a valuable food source to local predators and contribute to the local habitat by stabilizing stream beds and adding shells that can be used as shelter by smaller creatures. California's freshwater mussels have been challenged in recent years due to low water levels, warming temperatures and toxins in the sediment. Invasive Zebra mussels from Asia are also a threat to native mussels. At least one species, the western ridged mussel, is under consideration for federal Endangered Species Act protections.
“There isn't a lot of survey data about these freshwater mussel species in California,” said Kong. “We need to close that information gap. We plan to return to the SFPUC site in spring or summer to survey how the mussels are faring during the warmer months.”
The 23,000-acre SFPUC watershed is managed for water quality and is a protected area within the UNESCO Golden Gate Biosphere Reserve. This makes it a haven for at-risk aquatic species like freshwater mussels. Kong is hopeful that they might find western ridged mussel on their next survey there. While the team didn’t find the species at the site this time, they may simply have buried themselves in the sediment for the winter.
“The conditions for western pearlshell and western ridged mussels are the same: cool temperatures, high dissolved oxygen, low levels of toxins and flowing water,” said Kong. We found healthy western pearlshell adults and juveniles. If that species is thriving there, then western ridged mussels could be, too.”