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Species - Common (edible/blue) mussel
Common (edible/blue) mussel (Mytilus edulis)
An identifying feature of the species is the grouping in large aggregations forming mussel beds. The mussels play an important role as a habitat for other organisms. The mussels gather together in large numbers and use thin, sticky threads known as byssus to secure themselves to the rocks to reduce predation risk. New individuals may struggle to find a clear area on rocks to secure themselves, which means that the mussel beds will become layered and have been found to be 5 to 6 layers in depth. The impact of layering on the underneath mussels leads to fatality due to suffocation from the accumulation of silt and faeces. Once the mussels have died the dyssus that attaches them to the rocks will detach leaving them and the upper layer vulnerable to wave action, ripping them off and exposing an area of rock. This area can then also cause the surrounding mussels to be washed off by the changing tides.
The density of the mussels beds can cause variation in the size of mussels due to the competition for space and food. Temperature, salinity, wave and tidal exposure, and parasites can also effect size. The length can vary quite dramatically from 5 centimetres to 20 centimetres with an average size of 10 centimetres. A mussel’s life span can range from two to three years where predation pressure is high, but some individuals have been found to be 18 to 24 years. The mussels are preyed upon by starfish, sea urchins, crabs, fish, and birds. One of their main predators is the dog-whelk (Nucella lapillus), which grind a hole through its shell to turn the inner flesh into a soup that is sucked out. The mussels have found a way to defend themselves against the attack of the smaller predators. They use their byssus threads to stick to and flip over the predator. This immobilises it and leads to starvation and exposure to other predators.
The common or edible mussel is a popular and commercially fished species, which is now harvested from specially created beds. Mussels are filter feeders that feed off suspended organic particles in the water column. Filter feeding can cause the mussel to come into contact with and absorb containments, pathogens, viruses, and inorganic matter, which can make them harmful to humans making it highly important that they are cook thoroughly. The filter feeding has a positive impact on the surrounding water quality as they filter out the bacteria and plankton that accumulates in the water. Despite mussels being important to the fishing industry they can also be seen as a nuisance as they attach themselves to artificial structures including fishing crates and ropes and are very difficult to remove.
The mussel has a peak spawning period during spring and summer, which is timed to take advantage of the plankton blooms that occur through the spring months. A secondary spawning may occur and it is thought to be opportunistic as it depends on the environmental conditions and food availability. The larvae develop into a planktonic larval stage where they mature in the water column and will drift before settling. This usually takes place over 20 days during optimal conditions. Once settled the mussel will be developed enough and will secure itself to the rock and colony with its byssus.