Blue mussel

The blue mussel (Mytilus edulis), also known as the common mussel, is a medium-sized edible marine bivalve mollusc in the family Mytilidae, the only living family in the order Mytilida, known as "true mussels". These small creatures are very important for both nature and people. Many people enjoy eating blue mussels, and they are often farmed in special ways called aquaculture.

Blue mussels can be found in many parts of the world, from cold northern waters to warmer coastal areas. After they live their lives, the empty shells often wash up on beaches, which many people recognize from walks along the shore. These mussels play a big role in keeping ocean water clean and providing food for other sea animals.

Systematics and distribution

The blue mussel belongs to a group of closely related mussels called the Mytilus edulis complex. These mussels live along the coasts of the North Atlantic and North Pacific Oceans, in temperate to cold waters, and also along coasts in the Southern Hemisphere. Human activity has changed where some of these mussels are found. These mussels can sometimes mix and create hybrids when they live in the same area.

• Mytilus edulis sensu stricto: Native to the North Atlantic.
• Mytilus galloprovincialis: Native in the Mediterranean, the Black Sea, and Western Europe. Introduced in the temperate North Pacific, South Africa, and elsewhere in the Southern Hemisphere.
• Mytilus planulatus: Native to the Southern Hemisphere along the southern coast of Australia, Tasmania, and New Zealand.
• Mytilus platensis: Found in temperate and sub-Antarctic waters of South America and the Kerguelen Islands.
• Mytilus trossulus: Found in the North Pacific and northern parts of the North Atlantic and the Baltic Sea.

The Atlantic blue mussel is native to the North American Atlantic coast but is often found together with M. trossulus north of Maine. In Europe, it is found from the French Atlantic coast northwards to Novaya Zemlya and Iceland, but not in the Baltic Sea. In France and the British Isles, it sometimes mixes with M. galloprovincialis and also with M. trossulus.

Habitat

Blue mussels are small sea creatures that live in cold and mild water areas. They stick to rocks and hard surfaces using strong, stretchy threads made by special glands in their bodies. You can often find their empty shells on beaches.

Description

The blue mussel has a shell that is triangular and stretched out with soft, rounded edges. The shell is smooth and has thin lines running around it but no ridges going out from the center. These shells can be purple, blue, or sometimes brown, and they may have lines spreading out from the middle. The outside of the shell is covered by a thin layer that can wear away, showing the colorful layer underneath.

Blue mussels can stick to surfaces and also let go and stick again, which helps them move to better spots in the water.

Reproduction

Mussels have separate sexes. When they are ready, they release sperm and eggs into the water to create new mussels. Even though many sperm are released for each egg, most eggs are not fertilized. Only a small number of baby mussels grow up, as many are eaten by other animals before they can change into adult mussels.

When blue mussels are stressed or not healthy, they may stop making new babies or absorb the eggs and sperm they have made. The health of the parent mussels affects the baby mussels, especially if the water is too warm, polluted, or there isn’t enough food.

Monitor of environmental DNA damage

Blue mussels are helpful for checking ocean pollution because they collect many harmful substances from the water around them. When these mussels are exposed to certain metals like cadmium or chromium, it can damage their DNA and make it harder for them to fix this damage. Scientists study this to learn more about keeping our oceans safe.

Larval development

Larval development of blue mussels can take between 15 to 35 days, depending on conditions like salinity and temperature, as well as location. Larvae from Connecticut grow normally at temperatures between 15–20 °C (59–68 °F). At 15 °C (59 °F), normal development happens at salinities between 15 and 35 ppt, and at 35 ppt at 20 °C (68 °F).

The first stage is the ciliated embryo, which in 24 hours after fertilization forms the trochophore. It moves but still uses the yolk for food. The next stage, called the veliger, has a mouth and a gut, and uses cilia to filter food and move. A thin, clear shell forms, creating the straight hinge of the prodissoconch I shell. The veliger grows, forming the prodissoconch II shell. In the final veliger stage, the mussel develops light-sensitive spots and a long foot with a byssal gland.

When fully developed, the pediveliger’s foot touches a surface. If the surface is good, the larva changes into a juvenile form, called plantigrade, and attaches using byssus threads. The mussel stays attached until it grows to 1-1.5 mm long. This attachment is important for building blue mussel populations. In safe places, large groups of mussels can form beds that give shelter and food to other small sea animals. Byssal threads are made by byssal glands in the mussel’s foot from polyphenolic proteins, which help the threads stick.

Aggregation and mussel bed formation

Blue mussels often stick together using special threads called byssus. This helps them stay in place. When there aren't many mussels around, they form small clumps. When there are lots of mussels, they form dense groups called mussel beds.

Mussel beds can help protect mussels from waves and animals that might eat them. However, in very dense areas, mussels may grow more slowly because there isn't enough food. When they can, mussels move to areas where there are fewer mussels. Blue mussels can defend themselves against certain sea animals by making their shells stronger, but they have trouble if too many different animals attack them at once.

Uses and ecosystem services

Blue mussels help keep water clean because they eat tiny bits of dirt and harmful stuff from the water. People in many countries enjoy eating mussels, which come from both the wild and farms. Mussels are an important part of many dishes, especially in places like Spain, Portugal, France, Britain, the Netherlands, Belgium, Italy, and Turkey.

Mussels are also important for other sea creatures because they give them shelter and protect them. However, mussels are becoming less common in some areas, like the Gulf of Maine, which could be a problem for the environment. Changes in the ocean caused by too much carbon dioxide in the air might make it harder for mussels to grow and survive.