Common mussel (Mytilus edulis)
|Size||Length: up to 100 mm (2)|
Common and widespread; not listed under any conservation designations (2).
The common mussel has a roughly triangular shell, which is bluish, purplish or brown in colour and covered with a black outer layer (3). The inside of the shell is pearly, with a blue outer edge (2).
Extremely common around the coasts of Britain; very large commercial mussel beds occur in the Wash, Conway bay, Morecambe Bay, and estuaries of southwest England, west Scotland and west Wales (3). Elsewhere, it is found from the White Sea in northern Russia to southern France, and in the West Atlantic from Canada to North Carolina (3). It also occurs off Chile, the Falkland Isles, Argentina and the Kerguelen Isles (3).
The common mussel can be found from the middle shore to the shallow sublittoral zone, and attaches to substrates such as piers, rocks and stones with protein threads known as 'byssus' (2). It may also occur on soft sediments in estuaries, and large beds often form; mussels are farmed commercially in many areas (2).
The mussel is a filter-feeder; it filters bacteria, plankton, and detritus from the water (3). When large beds of this gregarious species form, individuals are bonded together with threads of byssus. Predation is the greatest cause of mortality; a range of predators take mussels, including dog-whelks (Nucella lapillus), crabs, sea urchins, star-fish, and birds such as the oystercatcher (Haematopus ostralegus) (3). Although mussels seem fairly defenceless, remarkably they are able to fend off marauding dog whelks and other predatory gastropods; a number of mussels work together to immobilise the predator with bysuss threads (3). Organisms that attach to mussels, such as seaweeds and barnacles, may increase the risk of the mussel becoming detached by wave action; however, mussels are able to sweep their foot over their shell, which may help to minimise the likelihood of such an organism becoming attached (3).
The sexes are separate, fertilisation occurs externally and spawning peaks in spring and summer (2). The larval stage is free-swimming and planktonic for around 4 weeks (2), before settling first on filamentous organisms such as seaweeds (3). After growing for a while, they detach and drift in the water on a long byssal thread; a mode of dispersal likened to that of young spiders floating through the air on a silk thread (2). After four weeks or so, the young mussel will have settled again, this time on a mussel bed (2). Young mussels are thought to have evolved primary settlement on filamentous substrates in order to avoid having to compete with adult mussels (3).
Mussels are host to the pea crab (Pinnotheres pisum), and a copepod (Mytilicola intestinalis), both of which are not parasites, as was once thought, but commensal organisms (they benefit from living with the mussel, but the mussel is not affected) (2). Furthermore, mussel beds provide habitats for a variety of marine life, and support higher levels of biodiversity than surrounding mudflats (3). The biodiversity of the bed increases with its size and age (3).
This species is currently widespread and not threatened.
Conservation action has not been targeted at this common species.
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- Commensal organisms: an interaction in which one species (the commensal) benefits from an association with a 'host' species, but the host is not affected.
- Larval: of the stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Plankton: aquatic organisms that drift with water movements; may be either phytoplankton (plants), or zooplankton (animals).
- Sublittoral: a marine zone between the littoral zone (the shallow zone where light reaches the bed, subject to submersion and exposure by tides) and depths of around 200m.
National Biodiversity Network Species Dictionary (August, 2002)
- Fish, J.D. and Fish, S. (1989) A student's guide to the seashore. 2nd Edition. Cambridge University press, Cambridge.
Tyler-Walters, H., 2002. Mytilus edulis. Common mussel. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. [on-line]. Plymouth: Marine Biological Association of the United Kingdom. (December, 2002)