Bivalve Buddies
By Emily Jankowski
Freshwater mussel in the stream.
For the rest of the ecosystem, salmon migration is something of a taxi service. Mostly this means bringing nutrients from the ocean upstream again, but some slower moving animals take it a bit more literally. The larval stage of freshwater mussels, known as glochidia, hitchhikes on fish in order to colonize new areas of streams and rivers. Don’t worry, the fish are not bothered by their passengers!
When ready, glochidia drop off of the fish and settle to the bottom to make a home among the sediment. Often mussels will use their foot to pull themselves into a position that offers them protection among the rocks while also giving them plenty of access to food in the current. Because mussels are filter feeders, they help to clean our waterways just by living in them! And for many animals, including otters, muskrats, and raccoons, mussels are a favorite meal. Piles of empty shells are a common site along mussel-bearing streams, hinting at the predators and prey you may not see. If they don’t get eaten first, mussels can live 60 or 70 years. Some individuals have even been known to reach 100 years old!
Emily excited to have found a western pearlshell!
Mussels can blend in easily with the rocks in the stream, but not too long ago we got lucky and noticed one in Friday Creek (pictured). It appears to be a western pearlshell mussel (Margaritifera falcata). Like most mussels in our region, it favors salmonids as a host for its glochidia stage. Perhaps this mussel was once attached to the gills of a chinook! And if we’re lucky, the salmon we help make good habitat for today will host the glochidia of future mussels-that will grow up to help clean the water for future salmon!
Freshwater mussels across the US are struggling to keep up in a world that once harvested their shells for buttons and continues to pollute and sediment load their waters. Many species are endangered. If you’re interested in freshwater mussels, check out @musselsPNW for more information, or this section of the Xerces Society website for additional resources.
