It feels slightly disingenuous to call these animals marine mussels because they do live in brackish water estuaries. However, it's worth separating them from freshwater mussels. Although they share a common name, marine mussels and freshwater mussels aren't closely related. In fact, marine mussels are more closely related to oysters and are also known as true mussels, while freshwater mussels are often known as clams.
Marine mussels live worldwide; however, they prefer temperate regions. There are more than 400 living species of these invertebrates. They range from shallow bays to deep-sea hydrothermal vents. Clams generally have a circular shape, while mussels tend to be more oblong. This helps them form huge aggregations. Although it's worth mentioning that there are also burrowing marine mussels who live in softer sediment. The marine mussels that remain sessile through their adult life gravitate towards hard structures such as rocks, while burrowing marine mussels can dig in sand as well as dead coral.
These invertebrates don't begin their life attached to something. Males and females release their sperm and eggs into the water column where they become fertilized externally. The eggs hatch into free-floating larvae that spend a few weeks to six months drifting through the sea. Then they settle somewhere soft, grow a bit more, and eventually find a more permanent location to spend their entire adult life. This is drastically different from freshwater mussels, who use lures to attract fish that their young then parasitize by clinging to the fish's gills. Don't worry; it doesn't hurt the fish. This difference is just another reason it's worth separating these similarly named animals.
Marine mussels are the bivalves you most likely associate with human consumption. People have been eating these animals for thousands of years. Farming practices of different species occur all around the world to provide plenty of mussel products to grocery stores and markets. Freshwater mussels, however, are described as tasting like an old dirty shoe.
Other predators to marine mussels include sea stars, welks, and other sea snails, as well as some species of seabirds. They also have to contend with parasites of their own, such as pea crabs who live inside their shell and eat the food they collect. Marine mussels are filter feeders. They draw in water and filter out phytoplankton before sending the water back out of their body. These animals need clean water to survive, so they're an excellent determining factor of a habitat's health. They can even become toxic if they consume toxic algae, which means that they can cause shellfish poisoning if they're not monitored by farmers.
Most farmed mussels take just under two years to raise to consumable size, which is about four inches in length. However, these mollusks can double that if left alone and reach more than a decade old. Marine mussels secure themselves to substrate via threadlike filaments. These allow the animals to hold steadfast to different structures so they can handle raging seas and crashing waves. Their shells arrange in H and often darken with age. Plus, depending on the species, they may sport ridges or a smooth shell. What's more, once opened, mussel males and females can be told apart. The lads are pale, and the ladies have orange flesh, which is tinted by their orange eggs.
