Mytilus spp. are marine bivalve molluscs. There are four species of Mytilus along the B.C. Coast. Three of these species, Mytilus edulis, Mytilus trossulus, and Mytilus galloprovincialis that can hybridize, therefore, they are commonly referred to as the Mytilus edulis complex. The distinctive fourth species, Mytilus californianus, is much larger growing up to 25 cm in length. In contrast, the more common Mytilus edulis rarely grows more than 11 cm in length.
Description:
These animals are enclosed in two separate blue-black or brown shells called "valves", hence the class name Bivalvia. The two shells are held together by a leathery hinge and strong interior muscles. The shells cover the entire soft body of the animal, including a lining of tissue that secretes the shell, an amorphous body that lacks a well-defined head but does have several layers of gills involved in gas exchange and feeding. When the valves open up the mussel can take in water to feed and obtain oxygen. During low tide or in the presence of a predator the shells will close tight, providing protection from predators and desiccation.
The adult mussels are typically sessile, attached to substratum with byssal threads. These strong sticky threads are somewhat flexible and can be used to move short distances and/or to tether predators, such as predatory snails, in place. Detached mussels use a small muscular foot that they can use to push themselves along the substratum until they reattach.
The adult mussels are typically sessile, attached to substratum with byssal threads. These strong sticky threads are somewhat flexible and can be used to move short distances and/or to tether predators, such as predatory snails, in place. Detached mussels use a small muscular foot that they can use to push themselves along the substratum until they reattach.
Ecology:
Mytilus spp. inhabit coastal areas from Alaska to California, where they can form mussel beds that are more than 30 cm deep. Of these three species, Mytilus trossulus may be the only native species in the Pacific Northwest and are most abundant on sheltered shorelines from the mid intertidal zone to subtidal depths of approximately 40 m. In contrast, Mytilus californianus, are most abundant on exposed shorelines.
Mytilus spp. are a dominant competitor that can occupy all of the available space on a rock, excluding other species such as barnacles and seaweeds. However, mussels also provide a moist, thermally-benign microhabitat for many other intertidal animals, such as periwinkles, shore crabs, sea anemone, marine worms and small fishes during low tide. And, during high tide, they provide protection from the stress of waves. So, the presence of mussel beds can enhance the overall biodiversity in an area.
Mytilus spp. are filter-feeders that feed on plankton. On the gills, millions of tiny hairs called cilia beat rhytmically to create a water current that draws more than 3L of seawater over the gills every hour. Mucus on the gills traps plankton that is moved to the mussel's mouth by the cilia.
In turn, adult Mytilus spp. are preyed upon by many intertidal and subtidal predators, such as predatory snails (e.g. Nucella lapillus), sea stars, crabs, fishes, birds (e.g. gulls) and mammals (e.g. Enhydra lutris). The mussels can defend themselves against predators by using their byssal threads to entangle predators. They can also anchor themselves more firmly to the substratum by growing more byssal threads (up to 50 per day) and by growing thicker shells.
Mytilus spp. have separate sexes, makes and females. Members of the M. edulis complex release billions of eggs and sperm into the water typically in late winter and early spring. M. californianus spawn throughout the year. Fertilized eggs develop into a free-floating larval stage, which can be transported hundreds of kilometers by ocean currents before settling to the ocean floor and completing development. Only about 1% of the fertilized larvae reach adulthood. The majority are eaten by filter-feeding predators, including other mussels.
Mytilus spp. are a dominant competitor that can occupy all of the available space on a rock, excluding other species such as barnacles and seaweeds. However, mussels also provide a moist, thermally-benign microhabitat for many other intertidal animals, such as periwinkles, shore crabs, sea anemone, marine worms and small fishes during low tide. And, during high tide, they provide protection from the stress of waves. So, the presence of mussel beds can enhance the overall biodiversity in an area.
Mytilus spp. are filter-feeders that feed on plankton. On the gills, millions of tiny hairs called cilia beat rhytmically to create a water current that draws more than 3L of seawater over the gills every hour. Mucus on the gills traps plankton that is moved to the mussel's mouth by the cilia.
In turn, adult Mytilus spp. are preyed upon by many intertidal and subtidal predators, such as predatory snails (e.g. Nucella lapillus), sea stars, crabs, fishes, birds (e.g. gulls) and mammals (e.g. Enhydra lutris). The mussels can defend themselves against predators by using their byssal threads to entangle predators. They can also anchor themselves more firmly to the substratum by growing more byssal threads (up to 50 per day) and by growing thicker shells.
Mytilus spp. have separate sexes, makes and females. Members of the M. edulis complex release billions of eggs and sperm into the water typically in late winter and early spring. M. californianus spawn throughout the year. Fertilized eggs develop into a free-floating larval stage, which can be transported hundreds of kilometers by ocean currents before settling to the ocean floor and completing development. Only about 1% of the fertilized larvae reach adulthood. The majority are eaten by filter-feeding predators, including other mussels.
To learn more:
Arribas, L.P., Donnarumma, L., Paloma, M.G., Scrosati, R.A. 2014. Intertidal mussels as ecosystem engineers: their associated invertebrate biodiversity under contrasting wave exposures. Marine Biodiversity 44: 203-211.
Barnes, R.D. 1987. Invertebrate Zoology, 5th edition. CBS College Publishing, New York, NY.
Leonard, G.H., Bertness, M.K., Yung, P.O. 1999. Crab predation, waterborne cues, and inducible defenses in the blue mussel, Mytilus edulis. Ecology 80(1): 1-14.