Most mussels you find at a grocery store or restaurant come from farms, not the wild. Global mussel production hit 1.91 million tonnes in 2023, with the vast majority raised through aquaculture in coastal waters. But mussels also exist naturally across every continent except Antarctica, living in both saltwater and freshwater environments with dramatically different life cycles depending on the species.
Where Mussels Live in the Wild
Marine mussels, the kind most people eat, attach themselves to hard surfaces in the intertidal zone, the strip of shoreline that’s underwater at high tide and exposed at low tide. They favor surf zones, clinging to exposed rocks, wooden pilings, and even other mussels at depths down to about 24 meters (79 feet). You’ll find them along rocky coastlines in temperate waters worldwide, from the North Atlantic and Mediterranean to the Pacific coasts of North and South America, New Zealand, and East Asia.
Three closely related species make up most of the world’s edible marine mussels. The blue mussel dominates in the North Sea and North Atlantic. The Mediterranean mussel thrives in warmer waters along southern Europe and parts of the Atlantic coast of Spain. A third species occupies colder Pacific waters. These species look nearly identical and can interbreed where their ranges overlap, which makes telling them apart surprisingly difficult without genetic testing.
Freshwater mussels are a completely different group, and North America is their global stronghold with more than 350 recognized species. The greatest diversity is found in flowing rivers and streams, particularly across the eastern and southeastern United States in systems like the Mississippi, Altamaha, Suwannee, and Flint rivers. Many freshwater species are found in only a single creek or watershed, making them extremely vulnerable to habitat loss. They are among the most endangered animals on the planet.
How Mussels Reproduce
Marine mussels broadcast spawn, releasing eggs and sperm directly into the water where fertilization happens by chance. The fertilized eggs develop into free-floating larvae that drift with ocean currents for several weeks before settling onto a hard surface and growing into the shelled mussels you’d recognize. They anchor themselves using tough, threadlike fibers called byssal threads, essentially gluing themselves in place.
Freshwater mussels have a far stranger life cycle. Males release sperm into the river current, and females downstream filter it in through their siphons to fertilize their eggs internally. The fertilized eggs develop into microscopic larvae called glochidia, which the female holds in her gills until they’re ready for release. Here’s the unusual part: those larvae are parasites. They must attach to the gills or fins of a specific host fish species within a couple of days, or they die. Once attached, they ride on the fish for anywhere from two weeks to several months, transforming into juvenile mussels before dropping off onto the riverbed to begin their adult lives.
Where Farmed Mussels Are Raised
Seven countries produce 90% of the world’s mussels: China leads by a wide margin, followed by Chile, Spain, New Zealand, France, Italy, and Thailand. Chile has grown into the second-largest producer largely through industrial-scale rope farming in its cold, nutrient-rich southern waters. Spain’s mussel industry is concentrated on floating rafts in the sheltered bays of Galicia. New Zealand farms its own distinctive green-lipped species.
In the United States, mussel farming is expanding along the coasts of New England, from Rhode Island to Maine. NOAA considers farmed blue mussels a sustainable seafood choice because of how they’re raised: mussels filter nutrients directly from the water, requiring no feed, fertilizer, or freshwater inputs. They actually improve local water quality as they grow.
How Mussels Are Farmed
The two main farming methods are rope-grown (also called longline) and bottom-grown, and the technique significantly affects the final product. Rope farming starts with collecting baby mussel “seed” on ropes placed near shore. Farmers pack this seed into mesh socks wrapped around long ropes, then suspend the socks from buoys in open water. The mussels grow inside the socks for at least a year, feeding on plankton filtered from the surrounding ocean. After a year, the mussels are bursting through the mesh and ready to harvest. Because they never touch the seafloor, rope-grown mussels tend to be cleaner, with thinner shells and plumper meat.
Bottom-grown mussels are seeded directly onto the ocean floor in managed beds. This is the older, more labor-intensive approach. The mussels develop thicker shells to protect against predators and sediment, and harvesting involves dredging them up from the bottom, which is muddier and messier work. Some dredging occurs in wild mussel harvesting too, though long-term environmental effects from this practice are considered rare.
How Mussels Get to Your Plate
Mussels are sold alive, which makes the supply chain a race against time. After harvest, rope-grown mussels are washed, separated from each other and any marine growth, then sorted by size. Depending on the bacterial levels in the harvest water and local regulations, they may go through depuration, a process where they’re held in clean seawater for up to 42 hours to flush out bacteria.
Before shipping, workers remove the byssal threads (the tough fibers mussels use to anchor themselves). Transport to market can take up to 48 hours, during which the mussels are kept cold and damp. Research into blue mussel supply chains found that keeping mussels alive during transit depends more on depuration and brief re-immersion in seawater before and after transport than on simply packing them in ice. Once they arrive at a distributor, mussels are either sold immediately, held in cold, humid storage, or re-immersed in seawater to improve their condition before sale. A typical journey from harvest to store takes about four days.
Invasive Mussels and Why They Matter
Not all mussels stay where they belong. Zebra mussels, native to the Caspian and Black Seas of southern Russia and Ukraine, arrived in the United States as stowaways in the ballast water of cargo ships. They’ve since spread across much of North America, clogging water intake pipes, coating boat hulls, and devastating native mussel populations. Because they reproduce by releasing microscopic larvae into the water, zebra mussels spread downstream with river currents. But they also hitchhike upstream with human help: invisible larvae travel in the water pooled inside boats, motors, and live wells, then establish new infestations wherever that water gets dumped.
The invasion has been catastrophic for native freshwater mussels, which were already in steep decline from dam construction, pollution, and habitat loss. Freshwater mussels now have among the highest extinction rates of any group of organisms on the planet, with dramatic, widespread population crashes documented across the continental United States.