Blue mussel

Blue mussel
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclass: Pteriomorphia
Order: Mytiloida
Family: Mytilidae
Subfamily: Mytilinae
Genus: Mytilus
Species: M. edulis
Binomial name
Mytilus edulis
Linnaeus, 1758

The blue mussel (Mytilus edulis), also known as the common mussel,[1] is a medium-sized edible marine bivalve mollusc in the family Mytilidae, the mussels. Blue mussels are subject to commercial use and intensive aquaculture.

Systematics and distribution

The Mytilus edulis complex

Systematically blue mussels consist of a group of (at least) three closely related taxa of mussels, known as the Mytilus edulis complex. Collectively they occupy both coasts of the North Atlantic (including the Mediterranean) and of the North Pacific in temperate to polar waters,[2] as well as coasts of similar nature in the Southern Hemisphere. The distribution of the component taxa has been recently modified as a result of human activity (invasive species). The taxa can hybridise with each other, if present at the same locality.

Mytilus edulis, strict sense

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

A genetically distinct lineage of M. edulis is present in the Southern Hemisphere, and has been attributed to subspecies Mytilus edulis platensis. This includes the Chilean mussel.[3]

Habitat

Blue mussels are boreo-temperate invertebrates that live in intertidal areas attached to rocks and other hard substrates by strong (and somewhat elastic) thread-like structures called byssal threads, secreted by byssal glands located in the foot of the mussel.

Description

The shape of the shell is triangular and elongate with rounded edges. The shell is smooth with a sculpturing of fine concentric growth lines but no radiating ribs. The shells of this species are purple, blue or sometimes brown in color, occasionally with radial stripes. The outer surface of the shell is covered by the periostracum which as eroded, exposes the colored prismatic calcitic layer. Blue Mussels are semi-sessile, having the ability to detach and reattach to a surface allowing the mollusk to reposition itself relative to the water position.

Reproduction

Mussels have separate sexes. Once the sperm and eggs are fully developed they are released into the water column for fertilization. Although there are about 10,000 sperm per egg,[4] large proportions of eggs deposited by blue mussel are never fertilized. As few as 1% of larvae that do mature ever reach adulthood, the majority are eaten by predators before completing metamorphosis.

The reproductive strategy seen in blue mussels is characteristic of planktotrophs, by minimizing nutrients in egg production to the bare minimum they are able to maximize the number of gametes produced. If the adult mussels are stressed during the beginning of gametogenesis, the process is terminated.[5] When stressed while fresh gametes are present, adult mussels reabsorb gametes. Larvae viability is also affected by the condition of parents: high water temperatures, pollutants and scarcity of food, during gamete production.[5] The reduction in viability is probably due to the lack of lipid reserves distributed to the eggs.

Larval development

Larval development can last from 15 to 35 days depending environmental conditions including salinity and temperature, as well as location. Larvae originating from Connecticut mature normally at 15–20 °C (59–68 °F), though at 15 °C (59 °F) normal development occurs at salinities between 15 and 35 ppt and 20 at 35 ppt at 20 °C (68 °F).[6]

The first stage of development is the ciliated embryo, which in 24-hours for fertilization form the trochophore. At this point although mobile, it is still reliant on the yolk for nutrients. Characterized by a functional mouth and alimentary canal the veliger stage also has cilia which are used for filtering food as well as propulsion. A thin translucent shell is secreted by the shell gland forming the notable straight hinge of the prodissoconch I shell. The veliger continues to mature forming the prodissoconch II shell. In the end stage of veliger development photosensitive eye spots and elongated foot with a byssal gland are formed.[7]

Once the pediveliger is fully developed, its foot extends and makes contact with substrate. The initial contact with the substrate is loose. If the substrate is suitable, the larva will metamorphoses into the juvenile form, plantigrade, and attach byssus threads. The mussel will remain in that state until reaching 1-1.5mm in length. This attachment is the prerequisite for the foundation for the blue mussel population. In sheltered environments large masses sometimes form beds which offer shelter and food for other invertebrates. Byssal thread are secreted by byssal glands located in the foot of the mussel, and are made up of polyphenolic proteins are proteins which serve as a bioadhesive.[7]

Aggregation

Blue mussels occasionally form clumps, or aggregates, of individuals when population density is low.The mussels attach to one another via collagenous protein strands called byssal threads. The aggregates are observed mostly in Mussel fields, which are short-lived populations of Mussels, usually exhibiting a clumped distribution pattern.[8] It is hypothesized that the mussels form these aggregates to increase reproductive success in low density populations.[9] This hypothesis, however, has yet to be conclusively proven. Alternative possible reasons for the behavior include resisting wave action and increasing water flow through the siphons of the mussel. The significance of the behavior is its relation to the formation of mussel beds from mussel fields. Mussel beds are persistent, dense mussel populations. Beds generally form from fields that persist long enough to establish a dense population.[8] Thus in areas where blue mussels are threatened, such as the Wadden Sea, it is of great importance to enhance the survival of mussel fields, of which mussel aggregates are the primary component.

Predators

Predation of blue mussels is greatest during the three weeks it spends as a planktonic larva. During this stage it is susceptible to jellyfish and fish larvae through adults. Once it metamorphoses the mussel is still restricted by predation, with smaller mussels with thinner, weaker shells most affected. Once the shells becomes stronger, blue mussels are preyed upon by sea stars such as Asterias vulgaris as well as by several species of sea gulls. The capability of shell thickening by mussels has become a very effective defense mechanism. In the presence of predators a mussel is able to increase shell thickness 5 to 10 percent, which in turn makes opening the shell take 50 percent more time.[10] Small mussels are also eaten by the dog whelk, Nucella lapillus.[11] The blue mussel is host to a wide range of parasites, but these parasites usually do not cause much damage.

Uses and ecosystem services

Boiled blue mussels in Normandy, France

Blue mussels are filter feeders and play a vital role in estuaries by removing bacteria and toxins. Mytilus edulis is commonly harvested for food throughout the world, from both wild and farmed sources. Mussels are a staple of many seafood dishes in various cuisines including Spanish (especially Galician), Portuguese, French, Dutch, Belgian and Italian. They are also commonly used as lab animals. Blue mussels were also harvested by the indigenous peoples of North America.[12]

References

  1. ↑ Paul Sterry (1997). Collins Complete Guide to British Wildlife. HarperCollins. ISBN 978-0-00-723683-1.
  2. ↑ Mathiesen, Sofie Smedegaard; Thyrring, Jakob; Hemmer-Hansen, Jakob; Berge, Jørgen; Sukhotin, Alexey; Leopold, Peter; Bekaert, Michaël; Sejr, Mikael Kristian; Nielsen, Einar Eg (October 2016). "Genetic diversity and connectivity within Mytilus spp. in the subarctic and Arctic". Evolutionary Applications. 10: 39–55. doi:10.1111/eva.12415.
  3. 1 2 Borsa, P.; Rolland, V.; Daguin-Thiebaut, C. (2012). "Genetics and taxonomy of Chilean smooth-shelled mussels, Mytilus spp. (Bivalvia: Mytilidae)". Comptes Rendus Biologies. 335 (1): 51–61. PMID 22226163. doi:10.1016/j.crvi.2011.10.002.
  4. ↑ Thompson, R.J. (1979). "Fecundity and reproductive effort in the blue mussel (Mytilus edulis), the sea urchin (Strongylocentrotus droebachiensis), and the snow crab (Chionoecetes opilio) from populations in Nova Scotia and Newfoundland". Journal of the Fisheries Research Board of Canada. 36 (8): 955–64. doi:10.1139/f79-133.
  5. 1 2 Bayne, B.; Widdows, J.; Thompson, R. (1976). "Physiological integrations". Marine mussels: their ecology and physiology. New York, NY: Cambridge University Press. pp. 261–91.
  6. ↑ Hrs-Brenko, M.; Calabrese, A. (1976). "The combined effects of salinity and temperature on larvae of the mussel Mytilus edulis". Marine Biology. 4 (3): 224–6. doi:10.1007/BF00393897.
  7. 1 2 Rzepecki, Leszek M.; Hansen, Karolyn M.; Waite, J. Herbert (August 1992). "Characterization of a cystine-rich polyphenolic protein family from the blue mussel Mytilus edulis L.". The Biological Bulletin. 183 (1): 123–37. JSTOR 1542413. doi:10.2307/1542413.
  8. 1 2 Nehls, Georg; Witte, Sophia; Büttger, Heike; Dankers, Norbert; Jansen, Jeroen; Millat, Gerald; Herlyn, Mark; Markert, Alexandra; Kristensen, Per Sand; Ruth, Maarten; Buschbaum, Christian; Wehrmann, Achim (2009). "Beds of blue mussels and Pacific oysters" (PDF). In Marencic, Harald; de Vlas, Jaap. Quality Status Report 2009. Wilhelmshaven: Common Wadden Sea Secretariat.
  9. ↑ Downing, John A.; Downing, William L. (1992). "Spatial Aggregation, Precision, and Power in Surveys of Freshwater Mussel Populations". Canadian Journal of Fisheries and Aquatic Sciences. 49 (5): 985–91. doi:10.1139/f92-110.
  10. ↑ Stokstad, E. (2006). "EVOLUTION: Native Mussel Quickly Evolves Fear of Invasive Crab". Science. 313 (5788): 745a. PMID 16902097. doi:10.1126/science.313.5788.745a.
  11. ↑ Petraitis, Peter S. (June 1987). "Immobilization of the Predatory Gastropod, Nucella lapillus, by Its Prey, Mytilus edulis". Biological Bulletin. 172 (3): 307–14. JSTOR 1541710.
  12. ↑ Robert Butler (1999) The Great Blue Heron (in Google Books)
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