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Native Oyster

Ostrea edulis Linnaeus 1758

Biology

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Native oysters are gregarious animals, and start their lives as males. They mature sexually as males between eight and ten months old. From then on, oysters will change sex regularly, depending on the water temperature. If the temperature reaches 16°C, they become females every three or four years. If the temperature reaches 20°C, they will change to females each year. They only revert to being males during the cooler intervening periods. Oysters may live for as long as 15 years but the usual lifespan is thought to be around six years. Eggs are stored and fertilised in the gill cavity of the female and remain there for a week before becoming free-swimming larvae and being released. The sperm is passed through the gills as part of the normal feeding process. The oyster larvae join the plankton in the open sea until, after 10 or 20 days, they find a surface to attach themselves. Adult oysters feed by filtration, sieving out the plankton using their gills. The towns of Colchester in Essex and Whitstable in Kent have become famous for their Oyster Festivals. Oysters have been an important food source since prehistory, and during the Roman occupation, British oysters were exported in large quantities back to Italy. One claim for eating them is that they act as an aphrodisiac, although there is no scientific proof for this argument.
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Conservation

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The oyster industry in the UK is a lucrative one, but is now dominated by the introduced Japanese or Pacific oyster Crassostrea giga. However, native oysters are farmed and potential sites are sometimes prepared by dumping broken shells, an aggregate known as 'cultch', which encourages young oysters, called 'spat', to form new beds. The native oyster is listed as a priority species in the UK Biodiversity Action Plan. The shell fishing industry in the UK is carefully regulated, and there is also a closed season on harvesting from 14 May to the 4 August during the critical spawning period, although this does not cover farmed oysters. The principal aims of the UK Action Plan for the native oyster are to maintain the current range of the oyster around the UK coastline and, where possible, increase the population and the number of viable oyster beds. In order to improve the species' chances, a number of laws and directives have been introduced in recent years. In 1987, a ban was imposed preventing the use of TBT-based anti-fouling paints on all vessels less than 25 metres in length. The ban was introduced for these smaller vessels as they are more likely to come into the shallower coastal waters than the larger sea-going ships. Shellfish farmers have welcomed the banning of the use of this paint, which is believed to affect the reproduction rates of oysters. There is also a European Directive governing the spread of diseases prevalent among bivalves. The shellfish industry is being encouraged to conduct more environmental impact assessments in areas thought suitable for re-introduction or, in some cases, on former sites that have become derelict.
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Description

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The native oyster is a bivalve mollusc, which means 'two shells', and is rough, scaly and yellowish-grey in colour. Each valve differs in shape and size; the left one (the one used by the oyster to attach itself to a surface) is concave, while the right one is flat and fits snugly inside the left. The right valve has concentric rings of a bluish colour, and the whole animal is roughly pear-shaped. Inside the shell, the colours range from blue to grey and include the opalescent 'mother of pearl'. Mother of pearl is secreted by the oyster around any foreign body that gets trapped between the shells, for example, a piece of sand or grit. In time, this builds up and forms a pearl.
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Habitat

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Oysters need a firm bedrock or an artificial equivalent along coastlines on which to fasten themselves, in water rich in plankton no deeper than 20 metres.
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Range

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Oysters are found widely around the western European coastline as far north as Spitsbergen, and south to Morocco and the Mediterranean. They can turn up all around the British coast with the best areas being the Thames Estuary, the west coast of Scotland, the Solent, the estuary of the River Fal, and Loch Foyle. They are also cultivated in other parts of the world such as North America, Japan and Australasia.
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Status

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Not protected. Listed as a priority species under the UK Biodiversity Action Plan.
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Threats

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Once a plentiful species around the UK coastline, the native oyster was the victim of serious overharvesting during the late 19th century, as they were a staple food of the poor and working classes. In the 15th century, fourpence would buy eight gallons of oysters, but by the beginning of the 20th century, they had become the expensive luxury they are today. This overfishing was probably a consequence of the expanding townships following the Industrial Revolution. Today the principal threat to the wild native oyster comes from disease and two introduced species, the American oyster drill shellfish Urosalpinx cinerea, and the slipper limpet Crepidula fornicata. The disease, Bonamiosis, is spread by a parasitic protozoan Bonamia ostreae. The oyster drill was brought to the UK by accident with imported American oysters and feeds on the young shellfish. The slipper limpet forms dense beds, competing with the oyster for spaces and food resources. It also produces a material known as 'mussel mud', a substance that covers potential oyster beds and makes it difficult for young oysters to establish themselves on a firm surface.
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Brief Summary

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There are very few wild flat oysters around anymore. They have become rare due to disease and competition with the Pacific oyster. The oyster shells on the beach are usually remnants from very old animals, dead already for many years. The shell has a rather regular shape, in contrast to the Pacific oyster which can have all kinds of sharp protrusions. The flat oyster is edible. For some people it is only a slimy bunch of salt but, according to oyster-lovers, it is the most delicious thing ever.
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Ostrea edulis

provided by wikipedia EN

Ostrea edulis, commonly known as the European flat oyster, is a species of oyster native to Europe. In the British Isles, regional names include Colchester native oyster, mud oyster, or edible oyster. In France, Ostrea edulis are known as huîtres plates (flat oysters) except for those that come from the Belon River estuary in Brittany, France, which are known as Belons.[3]

The fossil record of this species dates back to the Miocene (age range: 15.97 to 0.012 million years ago). These fossils have been found in Belgium, Italy, the Netherlands, Egypt, Greece, Spain, the United Kingdom, Austria, France and Germany.[4]

Description

When mature, O. edulis adults range from 3.8 to 11 centimetres (1.5 to 4.3 in) across.[5]

Shells are oval or pear shaped, white, yellowish or cream in colour, with a rough surface showing pale brown or bluish concentric bands on the right valve. The two valves are quite different in shape and size, as the left one is concave and fixed to the substratum, while the right one is almost flat and fits inside the left. The inner surface is smooth, whitish or bluish-grey.[6]

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Fossil of Ostrea edulis from Pliocene of Italy

Biology

Ostrea edulis are gregarious molluscs that start their lives as males. They mature sexually after eight–ten months and may change sex depending on the water temperature. Usually the lifespan can reach about six years, with a maximum of 15 years. Adult oysters feed by filtration.[7]

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Ostrea edulis; a) labial palpi b) gills c) mantle d) junction of the two folds of the mantle e) large adductor muscle f) the shell

Distribution

The species naturally ranges along the western and southern coasts of Europe from Norway to Morocco and including most of the British Isles and the Mediterranean coast.[8] Naturally viable populations have appeared in eastern North America from Maine to Rhode Island subsequent to artificial introduction in the 1940s and 1950s.[8]

Habitat

Ostrea edulis can be found in estuarine and shallow coastal water with hard substrata of mud and rocks.[9]

Human use

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Worldwide O. edulis harvest in tonnes, 1950–2003

Ostrea edulis has been harvested throughout Europe as an important food source since prehistory.[10] During Roman occupation of Britain O. edulis oysters were exported in large quantities back to Italy.[11] However, due to their robust nature and ease of cultivation the Pacific oysters, Crassostrea gigas, account for more than 75 percent of Europe's oyster production.

European flat oysters are famously grown in Brittany, France. The true Belon oyster is cultivated in the Belon River, France, and has the AOC protected name.[12] In the 1950s, Dutch scientists artificially introduced Belon oyster seed into the waters around Maine in hopes to establish a viable stock. The initial project was abandoned but ten years later natural colonies of flat oysters were found in the wild.[3] Many North American suppliers use the name 'Belon' to species that are found in the wild throughout the United States.

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Loch Ryan oysters are sourced from Scotland's only commercial European flat oyster bed.

Ostrea edulis is now also being maricultured in the states of California, Maine, and Washington in the United States. The species once dominated European oyster production but disease, pollution, and overfishing sharply reduced the harvest.[8]

U.S. oyster growers farm O. edulis in small quantities on both coasts. They are prized for their unique tannic seawater flavour, sometimes described as dry and metallic, and are more expensive than other American oysters.[8] The flavour is considered excellent for eating raw on the half shell.[13][14]

The adductor muscle of the European flat in combination with the shape of the shell results in a somewhat weaker seal compared with other oyster species. It is common practice to use rubber bands to prevent oysters from spilling their liquor and dehydrating in storage before consumption.[15]

See also

References

  1. ^ Linnaeus, Carl (1758). Systema Naturae (in Latin) (10 ed.). Uppsala: Linnaeus.
  2. ^ "ITIS Standard Report Page: Ostrea edulis". Retrieved 2008-08-06.
  3. ^ a b "Where do Belon Oysters come from and are they that rare?". Pangea Shellfish Company | Oyster and Shellfish Wholesale. Retrieved 2018-07-17.
  4. ^ Fossilworks
  5. ^ Jackson, Angus (2008-07-14). "Basic information for Ostrea edulis (Native oyster)". Plymouth: Marine Biological Association of the United Kingdom. Archived from the original on 2008-03-15. Retrieved 2008-08-07.
  6. ^ "FAO Fisheries & Aquaculture Ostrea edulis". www.fao.org. Retrieved 2018-07-09.
  7. ^ "Arkive.org". Archived from the original on 2015-06-08. Retrieved 2015-06-08.
  8. ^ a b c d "FAO Fisheries & Aquaculture Ostrea edulis". FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS. Retrieved 2008-08-06.
  9. ^ "MarLIN". Archived from the original on 2015-07-06. Retrieved 2015-06-08.
  10. ^ Hausmann, Niklas; Robson, Harry K.; Hunt, Chris (2019-09-30). "Annual Growth Patterns and Interspecimen Variability in Mg/Ca Records of Archaeological Ostrea edulis (European Oyster) from the Late Mesolithic Site of Conors Island". Open Quaternary. 5 (1): 9. doi:10.5334/oq.59. ISSN 2055-298X.
  11. ^ "European Flat Oyster – Ostrea edulis – Details – Encyclopedia of Life". Encyclopedia of Life. Retrieved 2017-10-28.
  12. ^ "Belon Oysters – Maine". www.chefs-resources.com. Retrieved 2017-10-28.
  13. ^ "Ostrea Edulis & Others – TIME". Time. 1964-07-31. Archived from the original on December 14, 2011. Retrieved 2008-08-07.
  14. ^ "Kelly Galway Oysters". Archived from the original on 2009-04-23. Retrieved 2008-08-07.
  15. ^ "Where do Belon Oysters come from and are they that rare?". Pangea Shellfish Company | Oyster and Shellfish Wholesale. Retrieved 2017-10-28.

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Ostrea edulis: Brief Summary

provided by wikipedia EN

Ostrea edulis, commonly known as the European flat oyster, is a species of oyster native to Europe. In the British Isles, regional names include Colchester native oyster, mud oyster, or edible oyster. In France, Ostrea edulis are known as huîtres plates (flat oysters) except for those that come from the Belon River estuary in Brittany, France, which are known as Belons.

The fossil record of this species dates back to the Miocene (age range: 15.97 to 0.012 million years ago). These fossils have been found in Belgium, Italy, the Netherlands, Egypt, Greece, Spain, the United Kingdom, Austria, France and Germany.

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Distribution

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North America, Western Atlantic Ocean
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bibliographic citation
Hayes, K.; Sliwa, C.; Migus, S.; McEnnulty, F.; Dunstan, P.; Heritagearkes, P. (2005). National priority pests. Part II, Ranking of Australian marine pests. Australian Government Department of the Environment and Heritage: Parkes. ISBN 1 876996 80 3. 94 pp. Hayes, K.; Sliwa, C.; Migus, S.; McEnnulty, F.; Dunstan, P.; Heritagearkes, P. (2005). National priority pests. Part II, Ranking of Australian marine pests. Australian Government Department of the Environment and Heritage: Parkes. ISBN 1 876996 80 3. 94 pp. Check List of European Marine Mollusca (CLEMAM). North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) Grosholz, E. D.; Crafton, R. E.; Fontana, R. E.; Pasari, J. R.; Williams, S. L.; Zabin, C. J. (2015). Aquaculture as a vector for marine invasions in California. <em>Biological Invasions.</em> 17(5): 1471-1484.
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