Some of the local beach residents, the Pacific blue mussels, have been in the headlines recently. Not unlike many human Americans, it seems they are threatened with homelessness.

Vashon and Maury beaches are currently home to thousands of these pretty shellfish, Mytilus trossulus, which usually live on boulders, beach cobbles or even driftwood logs on the upper beach. Unlike most other bivalves, such as butter clams and geoducks, mussels don’t bury themselves in sand. Instead, a tiny juvenile mussel settles out of seawater onto a surface, such as a rock or barnacle.

To hold on tightly to its chosen home site, a mussel secretes a strong substance called a byssal thread, which instantly adheres tightly and is waterproof. Secured with multiple byssal threads, the mussel can withstand even the strong, wind-driven waves of winter that roll rocks and driftwood across beaches, scouring the stones’ surfaces. Byssal threads are being studied by scientists who would like to learn, for medical reasons, how to synthesize threads that can adhere to surfaces under water equally well.

Usually, blue mussels settle together in clusters, and their byssal threads tie together little communities of stones, shellfish, bits of wood and seaweed and other small beach animals, such as amphipods (sand fleas), limpets, barnacles and snails (often the checkered periwinkles). On an expanse of beach consisting of small stones, which are vulnerable to dehydration in summer sun or displacement in winter waves, such communities are like oases of life, providing moisture and heightened stability for numerous tiny beach animals.

Moreover, the blue mussels perform several other important functions, including cleaning and filtering seawater by feeding continuously while they are inundated. They consume detritus and plankton, and are useful as an indicator species to test for paralytic shellfish poisoning because they rapidly accumulate the toxin, but when the bloom ends, they also rapidly clean the toxin out of their systems. And what’s really important to  people who love watching shoreline wildlife, mussels are a favorite food for many other species, including seastars, anemones, frilled dogwinkles, crabs, fish, ducks and shorebirds. And humans. They help sustain us all.

Sadly, research results released this spring by the University of Washington’s Friday Harbor laboratory indicate that one result of the increasing acidity of ocean water will be the weakening of the mussels’ byssal threads. Acidity caused by atmospheric carbon dioxide dissolving in the ocean is predicted to reach levels that have been shown in lab experiments to weaken the threads significantly and make them less stretchy. As mussels lose their grip on the beaches and disappear, one trickledown effect will likely be a reduction of other species on the beach too, both the small ones that live in mussel communities and the larger ones that prey on the communities.

We need a Vashon Household for beach life. What techniques can we employ to reduce the ecological impacts of 21st century change on blue mussels?  Next time you stroll on a beach take a look at one of their colonies. Peer closely to see what other critters and bits of material are included, and imagine this is a neighborhood that may not be capable of survival in 50 years.

— Rayna Holtz is a retired librarian and a Vashon Beach Naturalist.

Upcoming beach events

The art exhibit Between the Tides will bring an intertidal community alive within the walls of Ignition Gallery Friday evening between 6 and 9 p.m.  There will be a raffle and art contest with prizes, such as a guided beach walk, Low Tide Celebration shirts by Odin Lonning and a kayak tour.

On Saturday, Vashon Beach Naturalists will provide a beach program at Lisabeula. The event will enable elderly people or those who are physically disabled to sit in the shade of canopies and observe beach life carried by naturalists from the beach in containers of seawater. The tide will reach a low of -1.5 feet at about 11:30 a.m., enabling access to the hiding places of hermit crabs, limpets, anemones, sea urchins and many other shy critters of the lower beach area.