Photo: Will Husby
Shores
Blue Mussels
(Mytilus edulis)
Blue mussels are some of the bay’s most common observable sea creatures. They can be found in tight-packed aggregations at low tide on rocky shores, and on rocks almost anywhere along the edges of Kwilákm. They are an important food source for many sea and land creatures. Only strong predators are able to wrest them from their beds and break their hard shells.
Blue mussels can live from 18 to 24 years.
Mature blue mussels range from 5 to 10 cm—fitting easily into your hand. They grow quickly, taking from one to five years to reach maturity.
They occupy a broad variety of microhabitats, from the high intertidal where they are exposed to air and sunlight for many hours per day, to deeper subtidal regions where they are seldom exposed to the air. They thrive in a broad range of salinity, from lightly salted brackish water near the mouth of Terminal Creek to more salty oceanic seawaters found elsewhere in Atl’ka7tsem/Howe Sound.
Mussels living in intertidal zones tolerate extremes in temperature. In winter at low tide they are exposed to temperatures below freezing. In a normal summer the hot sun can shining on their black shells can be very hot. Studies show that adult mussels can tolerate temperatures up to 29oC for short periods.
Blue mussels resist drying up during low tide by tightly closing their shells, trapping a small amount of seawater within. If exposed to the air for a long time they open their shells slightly, breathing by passing air over their moist Gills.
Mussels are filter feeders, sucking in plankton and tiny particles of seaweeds and other organic materials that are suspended in seawater. They suck water in through their wide, fringed intake syphons and pump filtered water and their feces out their smaller excurrent syphons. Their fecal pellets, numbering in the millions, sink to the bottom, forming a fine grained sediment providing food and shelter for many bottom-dwelling sea creatures.
Like clams, blue mussels have a fleshy foot that they use to move about. But to protect themselves from being smashed about by waves, or being pried off rocks and eaten by crows, starfish, and sea birds, blue mussels deploy strong, silky byssal threads to attach to rocks, pilings, or other mussels. These threads are made by byssus glands, located within the mussel’s foot.
A mussel bed is held in place by thousands of byssal threads produced by the tightly-packed mussel. Individual mussels can move slowly by extending a byssal thread, using it as an anchor and then shortening it.
Mussel Armageddon
In June 2021, British Columbia, including Bowen Island, experienced an unprecedented heatwave. It peaked on June 28 and 29. Record temperatures of over 42oC were set in coastal areas on June 28. Unfortunately, these extreme air temperatures occurred on cloudless days and during extremely low tides. As a result, many intertidal creatures, including mussels, were killed, the result of being exposed to very long periods of intense sunlight which heated exposed rocks and the sea creatures living on them to temperatures in the upper 40oC. Dr. Christopher Harley, a marine ecologist, estimated that a billion intertidal marine creatures, including many blue mussels, were killed by the high heat.
Fortunately many mussel beds in deeper water and/or in shaded areas along the shore survived the heat wave. Hopefully they will thrive and their offspring will repopulate the devastated areas.
Mussels as Pollution Fighters
Scientists at Plymouth Marine Laboratory in the United Kingdom have launched a series of trials using blue mussels to clean up microplastic pollution.
Their experiments show that a cluster of 300 blue mussels (weighing 5 kg) could filter out over 250,000 microplastic particles per hour. The microplastics are then either ejected out their excurrent syphons within ‘pseudofeces’ or in their normal fecal matter. Even when their feces contain buoyant plastic, they rapidly sink out of the water. This means sediments containing microplastics could be dredged up taking microplastics out of the system entirely.