Question:

What is the purpose of oysters in the ocean?

Answer:

The hard surfaces of oyster shells and the nooks between the shells provide places where a host of small animals can live

More Info:

Oyster farming is an aquaculture (or mariculture) practice in which oysters are raised for human consumption. Oyster farming most likely developed in tandem with pearl farming, a similar practice in which oysters are farmed for the purpose of developing pearls. It was practiced by the ancient Romans as early as the 1st century BC on the Italian peninsula and later in Britain for export to Rome. The French oyster industry has relied on aquacultured oysters since the late 18th century. Commonly farmed food oysters include the Eastern oyster Crassostrea virginica, the Pacific oyster Crassostrea gigas, Belon oyster Ostrea edulis, the Sydney rock oyster Saccostrea glomerata, and the Southern mud oyster Ostrea angasi. Oysters naturally grow in estuarine bodies of brackish water. When farmed, the temperature and salinity of the water are controlled (or at least monitored), so as to induce spawning and fertilization, as well as to speed the rate of maturation – which can take several years. Three methods of cultivation are commonly used. In each case oysters are cultivated to the size of "spat," the point at which they attach themselves to a substrate. The substrate is known as a "culch" or "cultch". The loose spat may be allowed to mature further to form "seed" oysters with small shells. In either case (spat or seed stage), they are then set out to mature. The maturation technique is where the cultivation method choice is made. In one method the spat or seed oysters are distributed over existing oyster beds and left to mature naturally. Such oysters will then be collected using the methods for fishing wild oysters, such as dredging. In the second method the spat or seed may be put in racks, bags, or cages (or they may be glued in threes to vertical ropes) which are held above the bottom. Oysters cultivated in this manner may be harvested by lifting the bags or racks to the surface and removing mature oysters, or simply retrieving the larger oysters when the enclosure is exposed at low tide. The latter method may avoid losses to some predators, but is more expensive. In the third method the spat or seed are placed in a culch within an artificial maturation tank. The maturation tank may be fed with water that has been especially prepared for the purpose of accelerating the growth rate of the oysters. In particular the temperature and salinity of the water may be altered somewhat from nearby ocean water. The carbonate minerals and aragonite in the water may help oysters develop their shells faster and may also be included in the water processing prior to introduction to the tanks. This latter cultivation technique may be the least susceptible to predators and poaching, but is the most expensive to build and to operate. The Pacific oyster C. gigas is the species most commonly used with this type of farming. Since 1977, several boat builders in Brittany have built specialized amphibious vehicles for use in the area's mussel and oyster farming industries. The boats are made of aluminium, are relatively flat-bottomed, and have three, four, or six wheels, depending on the size of the boat. When the tide is out the boats can run on the tidal flats using their wheels. When the tide is in, they use a propeller to move themselves through the water. Oyster farmers in Jersey make use of similar boats. Currently, Constructions Maritimes du Vivier Amphibie has a range of models. Oyster harvesting using rakes (top) and sail driven dredges (bottom). From L'Encyclpédie of 1771 Oyster culture using tiles as culch. Taken from The Illustrated London News 1881 Department of Gironde (33) - Andernos-les-Bains, little boats of the oyster culturists (circa 1920) Harvesting oysters by hand on Willapa Bay, Washington, USA in October 1969 Purpose made oyster baskets Working on oysters at Belon, Brittany, France 2005 Oyster farm on Prince Edward Island Canada Oyster farm in South Australia Oyster boat in the harbour at Gorey, Jersey The farming of oysters and other shellfish is relatively benign or even restorative environmentally, and holds promise for relieving pressure on land-based protein sources. Restoration of oyster populations are encouraged for the ecosystem services they provide, including water quality maintenance, shoreline protection and sediment stabilization, nutrient cycling and sequestration, and habitat for other organisms. A native Olympia oyster restoration project is taking place in Liberty Bay, Washington, and numerous oyster restoration projects are underway in the Chesapeake Bay. In the U.S., Delaware is the only East Coast state without oyster aquaculture, but making aquaculture a state-controlled industry of leasing water by the acre for commercial harvesting of shellfish is being considered. Supporters of Delaware's legislation to allow aquaculture cite revenue, job creation, and nutrient cycling benefits. It is estimated that one acre can produce nearly 750,000 oysters, which could filter between 15 to 40 million gallons of water daily. Oyster predators include starfish, oyster drill snails, stingrays, Florida stone crabs, birds, such as oystercatchers, gulls, and humans. Pathogens that can affect either farmed C. virginica or C. gigas oysters include Perkinsus marinus (Dermo) and Haplosporidium nelsoni (MSX). However, C. viginicus are much more susceptible to Dermo or MSX infections than are the C. gigas species of oyster. Pathogens of O. edulis oysters include Marteilia refringens and Bonamia ostreae. In the north Atlantic Ocean, oyster crabs may live in an endosymbiotic commensal relationship within a host oyster. Since oyster crabs are considered a food delicacy they may not be removed from young farmed oysters, as they can themselves be harvested for sale. Polydorid polychaetes are known as pests of cultured oysters. Nineteenth century shallow draft sailboats designed primarily for oystering include: Also, from the 1880s on, the powerboat known as the Chesapeake Bay deadrise was a hull type used for oystering in the Chesapeake Bay of the United States.
The word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. The valves are highly calcified. Some kinds of oysters are commonly consumed, cooked or raw, by humans as a delicacy. Other kinds, such as pearl oysters, generally not eaten by humans, are harvested for the pearl produced within the mantle. First attested in English during the 14th century, the word "oyster" comes from Old French oistre, in turn from Latin ostrea, the feminine form of ostreum, which is the latinisation of the Greek ὄστρεον (ostreon), "oyster". Compare ὀστέον (osteon), "bone". True oysters are members of the family Ostreidae. This family includes the edible oysters, which mainly belong to the genera Ostrea, Crassostrea, Ostreola, and Saccostrea. Examples include the Belon oyster, eastern oyster, Olympia oyster, Pacific oyster, and the Sydney rock oyster. Almost all shell-bearing mollusks can secrete pearls, yet most are not very valuable. Pearl oysters are not closely related to true oysters, being members of a distinct family, the feathered oysters (Pteriidae). Both cultured pearls and natural pearls can be obtained from pearl oysters, though other molluscs, such as the freshwater mussels, also yield pearls of commercial value. The largest pearl-bearing oyster is the marine Pinctada maxima, which is roughly the size of a dinner plate. Not all individual oysters produce pearls naturally. In fact, in a harvest of three tons of oysters, only three to four oysters produce perfect pearls.][ In nature, pearl oysters produce natural pearls by covering a minute invading parasite with nacre, not by ingesting a grain of sand. Over the years, the irritating object is covered with enough layers of nacre to become a pearl. The many different types, colours and shapes of pearls depend on the natural pigment of the nacre, and the shape of the original irritant. Pearl farmers can culture a pearl by placing a nucleus, usually a piece of polished mussel shell, inside the oyster. In three to six years, the oyster can produce a perfect pearl. These pearls are not as valuable as natural pearls, but look exactly the same. In fact, since the beginning of the 20th century, when several researchers discovered how to produce artificial pearls, the cultured pearl market has far outgrown the natural pearl market. A number of bivalve molluscs (other than edible oysters and pearl oysters) also have common names that include the word "oyster", usually because they either taste or look like oysters, or because they yield noticeable pearls. Examples include: Crassostrea gigas Crassostrea gigas, opened Oysters are filter feeders, drawing water in over their gills through the beating of cilia. Suspended plankton and particles are trapped in the mucus of a gill, and from there are transported to the mouth, where they are eaten, digested, and expelled as feces or pseudofaeces. Oysters feed most actively at temperatures above 10°C (50°F). An oyster can filter up to 5 l (1.3 US gal) of water per hour. Chesapeake Bay's once-flourishing oyster population historically filtered excess nutrients from the estuary's entire water volume every three to four days. Today, that would take nearly a year. Excess sediment, nutrients, and algae can result in the eutrophication of a body of water. Oyster filtration can mitigate these pollutants. In addition to their gills, oysters can also exchange gases across their mantles, which are lined with many small, thin-walled blood vessels. A small, three-chambered heart, lying under the adductor muscle, pumps colorless blood to all parts of the body. At the same time, two kidneys, located on the underside of the muscle, remove waste products from the blood. While some oysters have two sexes (European oyster and Olympia oyster), their reproductive organs contain both eggs and sperm. Because of this, it is technically possible for an oyster to fertilize its own egg. The gonads surround the digestive organs, and are made up of sex cells, branching tubules, and connective tissue. Once the female is fertilized, she discharges millions of eggs into the water. The larvae develop in about six hours and swim around for about two to three weeks. After that, they settle on a bed and mature within a year. A group of oysters is commonly called a bed or oyster reef. As a keystone species, oysters provide habitat for many marine species. Crassostrea and Saccostrea live mainly in the intertidal zone, while Ostrea is subtidal. The hard surfaces of oyster shells and the nooks between the shells provide places where a host of small animals can live. Hundreds of animals, such as sea anemones, barnacles, and hooked mussels, inhabit oyster reefs. Many of these animals are prey to larger animals, including fish, such as striped bass, black drum and croakers. An oyster reef can increase the surface area of a flat bottom 50-fold. An oyster's mature shape often depends on the type of bottom to which it is originally attached, but it always orients itself with its outer, flared shell tilted upward. One valve is cupped and the other is flat. Oysters usually reach maturity in one year. They are protandric; during their first year, they spawn as males by releasing sperm into the water. As they grow over the next two or three years and develop greater energy reserves, they spawn as females by releasing eggs. Bay oysters usually spawn by the end of June. An increase in water temperature prompts a few oysters to spawn. This triggers spawning in the rest, clouding the water with millions of eggs and sperm. A single female oyster can produce up to 100 million eggs annually. The eggs become fertilized in the water and develop into larvae, which eventually find suitable sites, such as another oyster's shell, on which to settle. Attached oyster larvae are called spat. Spat are oysters less than 25 mm (0.98 in) long. Many species of bivalves, oysters included, seem to be stimulated to settle near adult conspecifics. Some tropical oysters in the family Isognomonidae grow best on mangrove roots. Low tide can expose them, making them easy to collect. In Trinidad in the West Indies, tourists are often astounded when they are told, in the Caribbean, "oysters grow on trees". The largest oyster-producing body of water in the United States is located in Chesapeake Bay, although these beds have decreased in number due to overfishing and pollution. Willapa Bay in Washington produces more oysters than any other estuary in the US. Other large oyster farming areas in the US include the bays and estuaries along the coast of the Gulf of Mexico from Apalachicola, Florida on the east to Galveston, Texas on the west. Large beds of edible oysters are also found in Japan and Australia. In 2005, China accounted for 80% of the global oyster harvest. Within Europe, France remained the industry leader. Common oyster predators include crabs, sea birds, starfish, and humans. Some oysters contain live crabs, known as oyster crabs. Bivalves, including oysters, are effective filter feeders and can have large effects on the water columns in which they occur. As filter feeders, oysters remove plankton and organic particles from the water column. Multiple studies have shown individual oysters are capable of filtering up to 50 gallons of water per day, and thus oyster reefs can significantly improve water quality and clarity. Oysters consume nitrogen-containing compounds (nitrates and ammonia), phosphates, plankton, detritus, bacteria, and dissolved organic matter, removing them from the water. What is not used for animal growth is then expelled as solid waste pellets, which eventually decompose into the atmosphere as nitrogen. In Maryland, the Chesapeake Bay Program plans to use oysters to reduce the amount of nitrogen compounds entering the Chesapeake Bay by 8,600 t (19,000,000 lb) per year by 2010. Several studies have shown that oysters and mussels have the capacity to dramatically impact nitrogen levels in estuaries. In the U.S., Delaware is the only East Coast state without aquaculture, but making aquaculture a state-controlled industry of leasing water by the acre for commercial harvesting of shellfish is being considered. Supporters of Delaware's legislation to allow oyster aquaculture cite revenue, job creation, and nutrient cycling benefits. It is estimated that one acre can produce nearly 750,000 oysters, which could filter between 57,000 to 150,000 m3 (15,000,000 to 40,000,000 US gal) of water daily. Also see nutrient pollution for an extended explanation of nutrient remediation. As an ecosystem engineer oysters provide "supporting" ecosystem services, along with "provisioning", "regulating" and "cultural" services. (See ecosystem services for service definitions and explanation.) Oysters influence nutrient cycling, water filtration, habitat structure, biodiversity, and food web dynamics. Oyster feeding and nutrient cycling activities could "rebalance" shallow, coastal ecosystems if restoration of historic populations could be achieved. Furthermore, assimilation of nitrogen and phosphorus into shellfish tissues provides an opportunity to remove these nutrients from the environment, but this benefit has only recently been recognized. In California's Tomales Bay, native oyster presence is associated with higher species diversity of benthic invertebrates but other ecosystem services have not been studied. As the ecological and economic importance of oyster reefs has become more widely acknowledged, creation of oyster reef habitat through restoration efforts has become more important- often with the goal of restoring multiple ecosystem services associated with natural oyster reefs. Middens testify to the prehistoric importance of oysters as food. In the United Kingdom, the town of Whitstable is noted for oyster farming from beds on the Kentish Flats that have been used since Roman times. The borough of Colchester holds an annual Oyster Feast each October, at which "Colchester Natives" (the native oyster, Ostrea edulis) are consumed. The United Kingdom hosts several other annual oyster festivals, for example Woburn Oyster Festival is held in September. Many breweries produce Oyster Stout, a beer intended to be drunk with oysters that sometimes includes oysters in the brewing process. The French seaside resort of Cancale is noted for its oysters, which also date from Roman times. Sergius Orata of the Roman Republic is considered the first major merchant and cultivator of oysters. Using his considerable knowledge of hydraulics, he built a sophisticated cultivation system, including channels and locks, to control the tides. He was so famous for this, the Romans used to say he could breed oysters on the roof of his house. In Ireland, it is traditional to eat them live with Guinness and buttered brown soda bread.][ In the early 19th century, oysters were cheap and mainly eaten by the working class. Throughout the 19th century, oyster beds in New York harbor became the largest source of oysters worldwide. On any day in the late 19th century, six million oysters could be found on barges tied up along the city’s waterfront. They were naturally quite popular in New York City, and helped initiate the city’s restaurant trade. New York's oystermen became skilled cultivators of their beds, which provided employment for hundreds of workers and nutritious food for thousands. Eventually, rising demand exhausted many of the beds. To increase production, they introduced foreign species, which brought disease; effluent and increasing sedimentation from erosion destroyed most of the beds by the early 20th century. Oysters’ popularity has put ever-increasing demands on wild oyster stocks. This scarcity increased prices, converting them from their original role as working-class food to their current status as an expensive delicacy. In the United Kingdom, the native variety (Ostrea edulis) is still held to be the finest,][ requiring five years to mature and protected by an Act of Parliament during the May–August spawning season. The current market is dominated by the larger Pacific oyster and rock oyster varieties which are farmed year round. Oysters are harvested by simply gathering them from their beds. In very shallow waters, they can be gathered by hand or with small rakes. In somewhat deeper water, long-handled rakes or oyster tongs are used to reach the beds. Patent tongs can be lowered on a line to reach beds that are too deep to reach directly. In all cases, the task is the same: the oysterman scrapes oysters into a pile, and then scoops them up with the rake or tongs. In some areas, a scallop dredge is used. This is a toothed bar attached to a chain bag. The dredge is towed through an oyster bed by a boat, picking up the oysters in its path. While dredges collect oysters more quickly, they heavily damage the beds, and their use is highly restricted. Until 1965, Maryland limited dredging to sailboats, and even since then motor boats can be used only on certain days of the week. These regulations prompted the development of specialized sailboats (the bugeye and later the skipjack) for dredging. Similar laws were enacted in Connecticut before World War 1 and lasted until 1969. The laws restricted the harvesting of oysters in state-owned beds to vessels under sail. These laws prompted the construction of the oyster sloop style vessel to last well into the 20th century. Hope, is believed to be the last built Connecticut oyster sloop, completed in 1948. Oysters can also be collected by divers. In any case, when the oysters are collected, they are sorted to eliminate dead animals, bycatch (unwanted catch), and debris. Then they are taken to market, where they are either canned or sold live. Oysters have been cultured for well over a century. The Pacific oyster, Crassostrea gigas, is presently the most widely grown bivalve around the world. Two methods are commonly used, release and bagging. In both cases, oysters are cultivated onshore to the size of spat, when they can attach themselves to a substrate. They may be allowed to mature further to form 'seed oysters'. In either case, they are then placed in the water to mature. The release technique involves distributing the spat throughout existing oyster beds, allowing them to mature naturally to be collected like wild oysters. Bagging has the cultivator putting spat in racks or bags and keeping them above the bottom. Harvesting involves simply lifting the bags or rack to the surface and removing the mature oysters. The latter method prevents losses to some predators, but is more expensive. The Pacific or Japanese oyster, Crassostrea gigas, has been grown in the outflow of mariculture ponds. When fish or prawns are grown in ponds, it takes, typically 10 kg (22 lb) of feed to produce 1 kg (2.2 lb) of product (dry-dry basis). The other 9 kg (20 lb) goes into the pond and after mineralization, provides food for phytoplankton, which in turn feeds the oyster. To prevent spawning, sterile oysters are now cultured by crossbreeding tetraploid and diploid oysters. The resulting triploid oyster cannot propagate, which prevents introduced oysters from spreading into unwanted habitats. In many areas, non-native oysters have been introduced in attempts to prop up failing harvests of native varieties. For example, the eastern oyster was introduced to California waters in 1875, while the Pacific oyster was introduced there in 1929. Proposals for further such introductions remain controversial. The Pacific oyster prospered in Pendrell Sound, where the surface water is typically warm enough for spawning in the summer. Over the following years, spat spread out sporadically and populated adjacent areas. Eventually, possibly following adaptation to the local conditions, the Pacific oyster spread up and down the coast and now is the basis of the North American west coast oyster industry. Pendrell Sound is now a reserve that supplies spat for cultivation. Near the mouth of the Great Wicomico River in the Chesapeake Bay, five year-old artificial reefs now harbor more than 180 million native Crassostrea virginica. That is far lower than in the late 1880s, when the bay’s population was in the billions, and watermen harvested about 910,000 m3 (25,000,000 imp bsh) annually. The 2009 harvest was less than 7,300 m3 (200,000 imp bsh). Researchers claim the keys to the project were: The oyster-tecture movement promotes the use of oyster reefs for water purification and wave attenuation. An "Oyster-tecture" project has been implemented at Withers Estuary, Withers Swash, South Carolina, by Neil Chambers-led volunteers, at a site where pollution was affecting beach tourism. Currently, for the installation cost of $3000, roughly 4.8 million liters of water are being filtered daily. In New Jersey, however, the Department of Environmental Protection refused to allow oysters as a filtering system in Sandy Hook Bay and the Raritan Bay, citing worries that commercial shellfish growers would be at risk and that members of the public might disregard warnings and consume tainted oysters. New Jersey Baykeepers responded by changing their strategy for utilizing oysters to clean up the waterway, by partnering with Naval Weapons Station Earle. The Navy station is under 24/7 security and therefore eliminates any poaching and associated human health risk. Oyster-tecture projects have been proposed to protect coastal cities, such as New York, from the threat of rising sea levels due to climate change. Jonathan Swift is quoted as having said, "He was a bold man that first ate an oyster", but evidence of oyster consumption goes back into prehistory, evidenced by oyster middens found worldwide. Oysters were an important food source in all coastal areas where they could be found, and oyster fisheries were an important industry where they were plentiful. Overfishing and pressure from diseases and pollution have sharply reduced supplies, but they remain a popular treat celebrated in oyster festivals in many cities and towns. It was once assumed that oysters were only safe to eat in months with the letter ‘r’ in their English and French names. This myth is based in truth, in that in the Northern Hemisphere, oysters are much more likely to spoil in May, June, July, and August. Oysters are an excellent source of zinc, iron, calcium, and selenium, as well as vitamin A and 12vitamin B. Oysters are low in food energy; one dozen raw oysters contains 110 kilocalories (460 kJ). Oysters are considered most nutritious when eaten raw. Traditionally, oysters are considered to be an aphrodisiac, partially because they resemble female sex organs. A team of American and Italian researchers analyzed bivalves and found they were rich in amino acids that trigger increased levels of sex hormones. Their high zinc content aids the production of testosterone. Dietary supplements may contain calcium carbonate from oyster shells, though no evidence shows this offers any benefits beyond what calcium may offer. Unlike most shellfish, oysters can have a fairly long shelf life of up to four weeks. However, their taste becomes less pleasant as they age. Oysters should be refrigerated out of water, not frozen, and in 100% humidity. Oysters stored in water under refrigeration will open, consume available oxygen, and die. Oysters must be eaten alive, or cooked alive. The shells of live oysters are normally tightly closed or snap shut given a slight tap. If the shell is open, the oyster is dead, and cannot be eaten safely. Cooking oysters in the shell kills the oysters and causes them to open by themselves. Traditionally, oysters that do not open have been assumed to be dead before cooking and therefore unsafe. However, according to at least one marine biologist, Nick Ruello, this advice may have arisen from an old, poorly researched cookbook's advice regarding mussels, which has now become an assumed truism for all shellfish. Ruello found 11.5% of all mussels failed to open during cooking, but when forced open, 100% were "both adequately cooked and safe to eat." Oysters can be eaten on the half shell, raw, smoked, boiled, baked, fried, roasted, stewed, canned, pickled, steamed, or broiled, or used in a variety of drinks. Eating can be as simple as opening the shell and eating the contents, including juice. Butter and salt are often added. In the case of oysters Rockefeller, preparation can be very elaborate. They are sometimes served on edible seaweed, such as brown algae. Care should be taken when consuming oysters. Purists insist on eating them raw, with no dressing save perhaps lemon juice, vinegar (most commonly shallot vinegar), or cocktail sauce. Upscale restaurants pair raw oysters with a home-made Mignonette sauce, which consists primarily of fresh chopped shallot, mixed peppercorn, dry white wine and lemon juice or sherry vinegar. Like fine wine, raw oysters have complex flavors that vary greatly among varieties and regions: sweet, salty, earthy, or even melon. The texture is soft and fleshy, but crisp on the palate. North American varieties include: Kumamoto and Yaquina Bay from Oregon, Malpeque from Prince Edward Island, Canada, Blue Point from Long Island, New York, and Cape May oysters from New Jersey. Salinity, mineral, and nutrient variations in the water that nurtures them influence their flavor profile. Oysters can contain harmful bacteria. Oysters are filter feeders, so will naturally concentrate anything present in the surrounding water. Oysters from the Gulf Coast of the United States, for example, contain high bacterial loads of human pathogens in the warm months, most notably Vibrio vulnificus and Vibrio parahaemolyticus. In these cases, the main danger is for immunocompromised individuals, who are unable to fight off infection and can succumb to septicemia, leading to death. Vibrio vulnificus is the most deadly seafood-borne pathogen, with a higher case-to-death ratio than even Salmonella enterica.][ Fresh oysters must be alive just before consumption or cooking. There is only one criterion: the oyster must be capable of tightly closing its shell. Open oysters should be tapped on the shell; a live oyster will close up and is safe to eat. Oysters which are open and unresponsive are dead and must be discarded. Some dead oysters, or oyster shells which are full of sand may be closed. These make a distinctive noise when tapped, and are known as 'clackers'. Opening oysters requires skill. The preferred method is to use a special knife (called an oyster knife, a variant of a shucking knife), with a short and thick blade about 5 cm (2.0 in) long. While different methods are used to open an oyster (which sometimes depend on the type), the following is one commonly accepted oyster-shucking method. Inexperienced shuckers can apply too much force, which can result in injury if the blade slips. Heavy gloves are necessary; apart from the knife, the shell itself can be razor sharp. Professional shuckers require less than three seconds to open the shell. If the oyster has a particularly soft shell, the knife can be inserted instead in the 'sidedoor', about halfway along one side where the oyster lips widen with a slight indentation. Opening or "shucking" oysters has become a competitive sport. Oyster-shucking competitions are staged around the world. Widely acknowledged to be the premiere event, the Guinness World Oyster Opening Championship is held in September at the Galway Oyster Festival. The annual Clarenbridge Oyster Festival 'Oyster Opening Competition' is also held in Galway, Ireland. The oyster is considered by some ethicists to be an appropriate food choice for those concerned with animal rights, arguing it is acceptable to eat oysters due to their lack of a central nervous system and the generally sustainable and environmentally friendly way in which they are raised and harvested. One common ethical objection to the consumption of animals is that their cultivation is environmentally harmful. Regarding environmental impact, 95% of oysters are sustainably farmed and harvested (other bivalves are frequently harvested by harmful dredging), feed on plankton (very low on the food chain), and in fact improve the marine environment by removing toxins. As such, farmed oysters are listed as a "Best Choice" (highest rating) on the Seafood Watch list. The view that oysters are acceptable to eat, even by strict ethical criteria, has notably been propounded in the seminal 1975 text Animal Liberation, by philosopher Peter Singer. However, subsequent editions have reversed this position (advocating against eating oysters). Singer has stated he has "gone back and forth on this over the years", and as of 2010, says, "while you could give them the benefit of the doubt, you could also say that unless some new evidence of a capacity for pain emerges, the doubt is so slight that there is no good reason for avoiding eating sustainably produced oysters". Oysters are subject to various diseases which can reduce harvests and severely deplete local populations. Disease control focuses on containing infections and breeding resistant strains, and is the subject of much ongoing research. Some oysters also harbor bacterial species which can cause human disease; of importance is Vibrio vulnificus, which causes gastroenteritis, which is usually self-limiting, and cellulitis. Cellulitis can be so severe and rapidly spreading, often it requires amputation. It is usually acquired when the contents of the oyster come in contact with a cut skin lesion, as when shucking an oyster. 29. OYSTER. Retrieved from Funk & Wagnalls New World Encyclopedia database.
The Pacific oyster, Japanese oyster or Miyagi oyster (Crassostrea gigas), is an oyster native to the Pacific coast of Asia. It has become an introduced species in North America, Australia, Europe, and New Zealand. The species name comes from the Greek crass meaning "thick", ostrea meaning "oyster" and gígās meaning "giant". The shell of Crassostrea gigas varies widely with the environment where it is attached. Its large, rounded, radial folds are often extremely rough and sharp. The two valves of the shell are slightly different in size and shape, the right valve being moderately concave. Shell colour is variable, usually pale white or off-white. Mature specimens can vary from 80 mm to 400 mm long. Crassostrea gigas is an estuarine species, but can also be found in intertidal and subtidal zones. They prefer to attach to hard or rocky surfaces in shallow or sheltered waters up to 40 m deep, but have been known to attach to muddy or sandy areas when the preferred habitat is scarce. The Pacific oyster can also be found on the shells of other animals. Larvae often settle on the shell of adults, and great masses of oysters can grow together to form oyster reefs. The optimum salinity for Pacific oysters is between 20 and 25 parts per thousand (ppt), and they can tolerant salinities as high as 35 ppt; at this level, however, reproduction is unlikely to occur. The Pacific oyster is also a very temperature tolerant species, as it can withstand a range from -1.8 to 35°C. The Pacific oyster has separate sexes, but hermaphrodites sometimes do exist. Their sex can be determined by examining the gonads, and it can change from year to year, normally during the winter months. In certain environmental conditions, one sex is favoured over the other. Protandry is favoured in areas of high food abundance and protogyny occurs in areas of low food abundance. In habitats with a high food supply, the sex ratio in the adult population tends to favour females, and areas with low food abundances tend to have a larger proportion of male adults. Spawning in the Pacific oyster occurs at 20°C. This species is very fecund, with females releasing about 50-200 million eggs in regular intervals (with a rate at 5-10 times a minute) in a single spawning. Once released from the gonads, the eggs move through the suprabranchial chambers (gills), are then pushed through the gill ostia into the mantle chamber, and finally are released in the water, forming a small cloud. In males, the sperm is released at the opposite end of the oyster, along with the normal exhalent stream of water. A rise in water temperature is thought to be the main cue in the initiation of spawning, as the onset of higher water temperatures in the summer results in earlier spawning in the Pacific oyster. The larvae of the Pacific oyster are planktotrophic, and are about 70 µm at the prodissoconch 1 stage. The larvae move through the water column via the use of a larval foot to find suitable settlement locations. They can spend several weeks at this phase, which is dependent on water temperature, salinity and food supply. Over these weeks, larvae can disperse great distances by water currents before they metamorphose and settle as small spat. Similar to other oyster species, once a Pacific oyster larva finds a suitable habitat, it attaches to it permanently using cement secreted from a gland in its foot. After settlement, the larva metamorphoses into a juvenile spat. The growth rate is very rapid in optimum environmental conditions, and market size can be achieved in 18 to 30 months. Unharvested Pacific oysters can live up to 30 years. The genome of Crassostrea gigas has been recently sequenced revealing an extensive set of genes that enable it to cope with environmental stresses. Crassostrea gigas was named by a Swedish naturalist, Carl Peter Thunberg in 1795. It originated from Japan, where it has been cultured for hundreds of years. It is now the most widely farmed and commercially important oyster in the world, as it is very easy to grow, environmentally tolerant and is easily spread from one area to another. The most significant introductions were to the Pacific Coast of the United States in the 1920s and to France in 1966. In most places, the Pacific oyster was introduced to replace the native oyster stocks which were seriously dwindling due to overfishing or disease. In addition, this species was introduced to create an industry that was previously not available at all in that area. As well as intentional introductions, the Pacific oyster has spread through accidental introductions either through larvae in ballast water or on the hulls of ships. In some places in the world, though, it is considered by some to be an invasive species, where it is outcompeting native species, such as the Olympia oyster in Puget Sound, Washington, the rock oyster, Saccostrea commercialis in the North Island of New Zealand and the blue mussel, Mytilus edulis, in the Wadden Sea. Numerous methods are used in the production of Pacific oysters. These techniques depend on factors such as the seed supply resources, the environmental conditions in the region and the market product, i.e., whether the oysters are sold in a half shell, or shelled for meat extraction. Production can either be entirely sea-based or rely on hatcheries for seed supply. Most of the global Pacific oyster spat supply comes from the wild, but some is now produced by hatchery methods. The seed from the wild can either be collected by the removal of seaweed from beaches or by hanging shell (cultch in suspension from long lines in the open water. The movement towards hatchery-reared spat is important, as wild seed is susceptible to changeable environmental conditions, such as toxic algal blooms, which can halt the supply of seed from that region. In addition, several pests have been noted as considerable dangers to oyster seed. The Japanese oyster drill (Ocenebra japonica), flatworm (Pseudostylochus osterophagus), and parasitic copepod (Mytlilcola orientalis) have been introduced accidentally to aquaculture areas, and have had serious impacts on oyster production, particularly in British Columbia and Europe. Pacific oyster broodstock in hatcheries are kept in optimum conditions so the production of large amounts of high quality eggs and sperm can be achieved. Pacific oyster females are very fecund, and individuals of 70-100g live weight can produce 50-80 million eggs in a single spawn. Broodstock adults are held in tanks at 20-22°C, supplied with cultured algae and with salinities of 25-32 ppt. These individuals can be induced to spawn by thermal shock treatment. Yet, it is more common for the eggs from a small sample of females (about six) to be stripped from the gonads using Pasteur pipettes and fertilized by sperm from a similar number of males. Pacific oysters have a pelagic veliger larval stage which lasts from 14–18 days. In the hatcheries, they are kept at temperatures of 25-28°C with an optimum salinity between 20 and 25‰. Early-stage veligers (<120 nm shell length) are fed daily with flagellate algae species (Isochrysis galbana or Pavlova lutherii) along with diatom species (either Chaetoceros calcitrans or Thalassiosira pseudonana). The larvae are close to a settlement stage when dark eye spots and a foot develop. During this time, settlement materials (cultch), such as roughed PVC sheets, fluted PVC pipes, or shells, are placed into the tanks to encourage the larvae to attach and settle. It is common, however, particularly on the US West Coast, for the mature larvae to be packed and shipped to oyster farms, where the farmers set the oysters themselves. Pacific oyster spat can be grown in nurseries by sea-based or land-based upwelling systems. Nursery culture reduces mortality in small spat, thus increasing the farm’s efficiency. Sea-based nursery systems are often located in estuarine areas where the spat are mounted on barges or rafts. Land-based nursery systems have spat mounted on barges in large saltwater tanks, which either have a natural algae supply or are enriched with nutrients from fertilizers. This stage of oyster culture is almost completely sea-based. A range of bottom, off-bottom, suspended and floating cultures are used. The technique used depends on site-specific conditions, such as tidal range, shelter, water depth, current flow and nature of substratum. Pacific oysters take 18– 30 months to develop to the market size of 70-100 g live weight (shell on). Growth from spat to adults in this species is very rapid at temperatures of 15-25°C and at salinities of 25 to 32 ppt. In 2000, the Pacific oyster accounted for 98% of the world’s cultured oyster production, and is produced in countries all over the world. Global production has increased from about 150 tonnes in 1950 to 750 tonnes in 1980. By 2003, global production had increased to 4.38 million tonnes. The majority was in China, which produced 84% of the global production. Japan, France and the Republic of Korea also contributed, producing 261 000, 238 000 and 115 000 tonnes produce, respectively. The other two major producers are the United States (43 000 tonnes) and Taiwan (23 000 tonnes). In 2003, global Pacific oyster production was worth $ 3.69 billion, with Asia contributing over half of this amount. Pacific oysters are nonspecific filter feeders, which means they ingest any particulate matter in the water column. This presents major issues for virus management of open water shellfish farms, as shellfish like the Pacific oyster have been found to contain norovirus strains which can be harmful to humans. Globally, noroviruses are the most common cause of nonbacterial gastroenteritis, and are introduced into the water column by faecal matter, either from sewage discharge or land runoff from nearby farmland. Numerous gastroenteritis outbreaks in the world have been directly caused by the consumption of shellfish from polluted areas. Pacific oysters, like other shellfish, are able to remove heavy metals, such as zinc and copper, as well as biotoxins (microscopic toxic phytoplankton), from the surrounding water. These can accumulate in the tissues of the animal and leave it unharmed (bioaccumulation). However, when the concentrations of the metals or biotoxins are high enough, shellfish poisoning can result when they are consumed by humans. Most countries have strict water regulations and legislation to minimise the occurrence of such poisoning cases. Numerous predators are known to damage Pacific oyster stocks. Several crab species (Metacarcinus magister, Cancer productus, Metacarcinus gracilis), oyster drills and starfish species (Pisater ochraceus, P. brevispinus, Evasterias troschelii and Pycnopodia helianthoides) can cause severe impacts to oyster culture. Productivity of the Pacific oyster can be discussed as the amount of meat produced in relation to the amount of seed planted on cultch. The productivity of a farm also depends on the interaction of biotic factors, such as mortality, growth, and oyster size, as well as the quality of the seed and the growing technique used (off bottom, bottom, suspended or floating culture). The main causes of mortality in the Pacific oystere are: natural mortality (age), predators, disease, environmental conditions (ice, freak winds), competition for space (crowding of cultch), silting (sediment runoff from land) and cluster separation (process of breaking up clusters of oysters to into as many individual oysters as possible). In New Zealand, the Pacific oyster was unintentionally introduced in 1950s, most likely through ballast water and from the hulls of ships. Aquaculture farmers at the time noticed the Pacific oyster outcompeted the endemic species, the Sydney rock oyster (Saccostrea glomerata), which naturally occurs in intertidal areas in the North Island. Early experiments in rock oyster cultivation procedures attached spat to cement-covered sticks and laid them down in racks. The farmers noticed, however, the Pacific oyster outgrew the endemic species in most areas, and constantly was attaching to the rock oyster collection sticks. A few years later, Pacific oysters were the dominant species in the farms, as it grew three times faster than the rock oyster, produced a reliable and constant supply of spat, and had an already established market overseas. In 1977, the Pacific oyster was accidentally introduced to the Marlborough Sounds, and farming began there in the 1990s. Marlborough farmers developed a different method of cultivation in comparison to the North Island method of racks; they instead suspended their oysters on longlines. The Pacific oyster is one of the three main aquaculture species in New Zealand along with king salmon and the greenshell mussels. Pacific oyster aquaculture production has grown from an export value of $11 million in 1986 to $32 million in 2006. In 2006, the 23 Pacific oyster farms throughout New Zealand covered a total of 750 hectares of marine space and produced 2,800 tonnes of product per year. Annual production is now between about 3,300 and 4,000 tonnes. In 2005, the value of New Zealand's Pacific oyster production was $12 million domestically, and $16.9 million for export. New Zealand’s main export markets are Japan, Korea, the US, the EU and Australia.
A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer created by an animal that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on beaches by beachcombers. The shells are empty because the animal has died and the soft parts have been eaten by another animal or have rotted out. The term seashell usually refers to the exoskeleton of an invertebrate (an animal without a backbone). Most shells that are found on beaches are the shells of marine mollusks, partly because many of these shells endure better than other seashells. Apart from mollusk shells, other shells that can be found on beaches are those of barnacles, horseshoe crabs and brachiopods. Marine annelid worms in the family Serpulidae create shells which are tubes made of calcium carbonate that are cemented onto other surfaces. The shells of sea urchins are called tests, and the moulted shells of crabs and lobsters are called exuviae. While most seashells are external, some cephalopods have internal shells. Seashells have been used by humans for many different purposes throughout history and pre-history. However, seashells are not the only kind of shells; in various habitats it is possible to find shells from freshwater animals such as freshwater mussels and freshwater snails, and it is also possible to find the shells of land snails. When the word "seashells" is used to refer only to the shells of marine mollusks then studying seashells is part of conchology. Conchologists or serious collectors who have a scientific bias are in general careful not to disturb living populations and habitats: even though they may collect a few live animals, most responsible collectors do not often over-collect or otherwise disturb ecosystems. When studying the whole molluscan animal is included as well as studying the shell, then the study is known as malacology; a person who studies mollusks is known as a malacologist. Seashells are commonly found in beach drift, which is natural detritus deposited along strandlines on beaches by the waves and the tides. Shells are very often washed up onto a beach empty and clean, the animal having already died, and the soft parts having rotted away or having been eaten by either predators or scavengers. Empty seashells are often picked up by beachcombers. However, the majority of seashells which are offered for sale commercially have been collected alive (often in bulk) and then killed and cleaned, specifically for the commercial trade.][ This type of large-scale exploitation can sometimes have a strong negative impact on local ecosystems, and sometimes can significantly reduce the distribution of rare species. The word seashell is often used to mean only the shell of a marine mollusk. Marine mollusk shells that are familiar to beachcombers and thus most likely to be called "seashells" are the shells of marine species of bivalves (or clams), gastropods (or snails), scaphopods (or tusk shells), polyplacophorans (or chitons), and cephalopods (such as nautilus and spirula). These shells are very often the most commonly encountered, both in the wild, and for sale as decorative objects. Marine species of gastropods and bivalves are more numerous than land and freshwater species, and the shells are often larger and more robust. The shells of marine species also often have more sculpture and more color, although this is by no means always the case. In the tropical and sub-tropical areas of the planet, there are far more species of colorful, large, shallow water shelled marine mollusks than there are in the temperate zones and the regions closer to the poles. Although there are a number of species of shelled mollusks that are quite large, there are vast numbers of extremely small species too, see micromollusks. Not all mollusks are marine however, there are numerous land and freshwater mollusks, see for example snail and freshwater bivalves. And not all mollusks have an external shell: some mollusks such as some cephalopods (squid and octopuses) have an internal shell, and many mollusks have no shell, see for example slug and nudibranch. Bivalves are often the most common seashells that wash up on large sandy beaches or in sheltered lagoons. They can sometimes be extremely numerous. Very often the two valves become separated. There are more than 15,000 species of bivalves that live in both marine and freshwater. Examples of bivalves are clams, scallops, mussels, and oysters. The majority of bivalves consist of two identical shells that are held together by a flexible hinge. Inside the shells holds the animal’s body. Bivalves that do not have two shells either have one shell or they lack a shell all together. The shells are made of calcium bicarbonate and are secreted by the mantle. Bivalves, also known as pelecypods, are mostly filter feeders; they draw in water through their gills which then traps tiny food particles. Some bivalves have eyes and even an open circulatory system. Bivalves are used all over the world as types of food and as a way of getting pearls. But in the water, the larvae of some freshwater mussels can be dangerous to fish and can even bore through wood. Shell Beach, Western Australia is a beach which is entirely made up of the shells of the cockle Fragum erugatum. Certain species of gastropod seashells (the shells of sea snails) can sometimes be common, washed up on sandy beaches, and also on beaches that are surrounded by rocky marine habitat. Chiton plates or valves often wash up on beaches in rocky areas where chitons are common. Chiton shells, which are composed of eight separate plates and a girdle, usually come apart not long after death, so they are almost always found as disarticulated plates. Plates from larger species of chitons are sometimes known as "butterfly shells" because of their shape. Only a few species of cephalopods have shells (either internal or external) that are sometimes found washed up on beaches. Some cephalopods such as Sepia, the cuttlefish, have a large internal shell, the cuttlefish bone, and this often washes up on beaches in parts of the world where cuttlefish are common. Spirula spirula is a deep water squid-like cephalopod. It has an internal shell which is small (about 1 in or 24 mm) but very light and buoyant. This chambered shell floats very well and therefore washes up easily and is familiar to beachcombers in the tropics. Nautilus is the only genus of cephalopod that has a well-developed external shell. Females of the cephalopod genus Argonauta create a papery egg case which sometimes washes up on tropical beaches and is referred to as a "paper nautilus". The largest group of shelled cephalopods, the ammonites, are extinct, but their shells are very common in certain areas as fossils. Empty molluscan seashells are a sturdy, and usually readily available, "free" resource which is often easily found on beaches, in the intertidal zone, and in the shallow subtidal zone. As such they are sometimes used second-hand by animals other than humans for various purposes, including for protection (as in hermit crabs) and for construction. There are numerous popular books and field guides on the subject of shell-collecting. Although there are a number of books about land and freshwater mollusks, the majority of popular books emphasize, or focus exclusively on, the shells of marine mollusks. Both the science of studying mollusk shells and the hobby of collecting and classifying them are known as conchology. The line between professionals and amateur enthusiasts is often not well defined in this subject, because many amateurs have contributed to, and continue to contribute to, conchology and the larger science of malacology. Many shell collectors belong to "shell clubs" where they can meet others who share their interests. A large number of amateurs collect the shells of marine mollusks, and this is partly because many shells wash up empty on beaches, or live in the intertidal or sub-tidal zones, and are therefore easily found and preserved without much in the way of specialized equipment or expensive supplies. Some shell collectors find their own material and keep careful records, or buy only "specimen shells", which means shells which have full collecting data: information including how, when, where, in what habitat, and by whom, the shells were collected. On the other hand, some collectors buy the more widely available commercially-imported exotic shells, the majority of which have very little data, or none at all. To museum scientists, having full collecting data (when, where, and by whom it was collected) with a specimen is far more important than having the shell correctly identified. Some owners of shell collections hope to be able to donate their collection to a major natural history or zoology museum at some point, however, shells with little or no collecting data are usually of no value to science, and are likely not to be accepted by a major museum. Apart from any damage to the shell that may have happened before it was collected, shells can also suffer damage when they are stored or displayed. For an example of one rather serious kind of damage see Byne's disease. There are a number of clubs or societies which consist of people who are united by a shared interest in shells. In the US these clubs are more common in southerly coastal areas, such as Florida and California, where the marine fauna is rich in species. Seashells are usually identified by consulting general or regional shell-collecting field guides, and specific scientific books on different taxa of shell-bearing mollusks (monographs) or "iconographies" (limited text - mainly photographs or other illustrations). (For a few titles on this subject in the US, see the list of books at the foot of this article.) Identifications to the species level are generally achieved by examining illustrations and written descriptions, rather than by the use of Identification keys, as is often the case in identifying plants and other phyla of invertebrates. The construction of functional keys for the identification of the shells of marine mollusks to the species level can be very difficult, because of the great variability within many species and families. The identification of certain individual species is often very difficult, even for a specialist in that particular family. Some species cannot be differentiated on the basis of shell character alone. Numerous smaller and more obscure mollusk species (see micromollusk) are yet to be discovered and named. In other words, they have not yet been differentiated from similar species and assigned scientific (binomial) names in articles in journals recognized by the International Commission on Zoological Nomenclature (ICZN). Large numbers of new species are published in the scientific literature each year. There are currently an estimated 100,000 species of mollusks worldwide. The term seashell is also applied loosely to mollusk shells that are not of marine origin, for example by people walking the shores of lakes and rivers using the term for the freshwater mollusk shells they encounter. Seashells purchased from tourist shops or dealers may include various freshwater and terrestrial shells as well. Non-marine items offered may include large and colorful tropical land snail shells, freshwater apple snail shells, and pearly freshwater unionid mussel shells. This can be confusing to collectors, as non-marine shells are often not included in their reference books. Seashells have been used as a medium of exchange in various places, including many Indian Ocean and Pacific Ocean islands, also in North America, Africa and the Caribbean. Seashells have often been used as tools, because of their strength and the variety of their shapes. Because seashells are in some areas a readily available bulk source of calcium carbonate, shells such as oyster shells are sometimes used as soil conditioners in horticulture. The shells are broken or ground into small pieces in order to have the desired effect of raising the pH and increasing the calcium content in the soil. Seashells have played a part in religion and spirituality, sometimes even as ritual objects. Seashells have been used as musical instruments, wind instruments for many hundreds if not thousands of years. Most often the shells of large sea snails are used, as trumpets, by cutting a hole in the spire of the shell or cutting off the tip of the spire altogether. Various different kinds of large marine gastropod shells can be turned into "blowing shells", however the most commonly encountered species used as "conch" trumpets are: Whole seashells or parts of sea shells have been used as jewelry or in other forms of adornment since prehistoric times. Mother of pearl was historically primarily a seashell product, although more recently some mother of pearl comes from freshwater mussels. Also see pearl. "Sailor's Valentines" were late 19th century decorative keepsakes which were made in the Caribbean, and which were often purchased by sailors to give to their loved ones back home for example in England. These valentines consisted of elaborate arrangements of small seashells glued into attractive symmetrical designs, which were encased on a wooden (usually octagonal) hinged box-frame. The patterns used often featured heart-shaped designs, or included a sentimental expression of love spelled out in small shells. The making of shellwork artifacts is a practice of Aboriginal women from La Perouse in Sydney, New South Wales, dating back to the 19th century. Shellwork objects include baby shoes, jewelry boxes and replicas of famous landmarks, including the Sydney Harbour Bridge and the Sydney Opera House. The shellwork tradition began as an Aboriginal women's craft which was adapted and tailored to suit the tourist souvenir market, and which is now considered high art. Small pieces of colored and iridescent shell have been used to create mosaics and inlays, which have been used to decorate walls, furniture and boxes. Large numbers of whole seashells, arranged to form patterns, have been used to decorate mirror frames, furniture and man-made grottos. A very large outdoor sculpture at Akkulam of a gastropod seashell is a reference to the sacred chank shell Turbinella pyrum of India. Maggi Hambling designed a striking 13 ft (4 m) high sculpture of a scallop shell which stands on the beach at Aldeburgh, in England. The goddess of love, Venus or Aphrodite is often traditionally depicted rising from the sea on a seashell. In the Birth of Venus (Botticelli), Botticelli depicted the goddess Venus rising from the ocean on a scallop shell. Sea shells found in the creek and backwater of the coast of west India are used as an additive to poultry feed. They are crushed and mixed with jawar maaze and dry fish.][ Many arthropods have sclerites, or hardened body parts, which form a stiff exoskeleton made up mostly of chitin. In crustaceans, especially those of the class Malacostraca (crabs, shrimps and lobsters, for instance), the plates of the exoskeleton may be fused to form a more or less rigid carapace. Moulted carapaces of a variety of marine malacostraceans often wash up on beaches. The horseshoe crab is an arthropod of the family Limulidae. The shells or exuviae of these arachnids are common in beach drift in certain areas of the world. Some echinoderms such as sea urchins, including heart urchins and sand dollars, have a hard "test" or shell. After the animal dies, the flesh rots out and the spines fall off, and then fairly often the empty test washes up whole onto a beach, where it can be found by a beachcomber. These tests are fragile and easily broken into pieces. The brachiopods, or lamp shells, superficially resemble clams, but the phylum is completely unrelated to mollusks. Most lines of brachiopods ended during the Permian-Triassic extinction event, and their ecological niche was filled by bivalves. A few of the remaining species of brachiopods occur in the low intertidal zone and thus can be found live by beachcombers. Some polychaetes, marine annelid worms in the family Serpulidae, secrete a hard tube made of calcium carbonate, adhering to stones or other shells. This tube resembles, and can be confused with, the shell of marine gastropod mollusks in the family Vermetidae, the worm snails. A few other categories of marine animals leave remains which might be considered "seashells" in the widest possible sense of the word. Sea turtles have a carapace and plastron of bone and cartilage which is developed from their ribs. Infrequently a turtle "shell" will wash up on a beach. Pieces of the hard skeleton of corals commonly wash up on beaches in areas where corals grow. The construction of the shell-like structures of corals are aided by a symbiotic relationship with a class of algae, zooxanthellae. Typically a coral polyp will harbor particular species of algae, which will photosynthesise and thereby provide energy for the coral and aid in calcification, while living in a safe environment and using the carbon dioxide and nitrogenous waste produced by the polyp. Coral bleaching is a disruption of the balance between polyps and algae, and can lead to the breakdown and death of coral reefs. The skeletons of soft corals such as gorgonians, also known as sea fans and sea whips, commonly wash ashore in the tropics after storms. Plant-like diatoms and animal-like radiolarians are two forms of plankton which form hard silicate shells. Foraminifera and coccolithophore create shells known as "tests" which are made of calcium carbonate. All these shells and tests are usually (but in the case of foraminifera not always) microscopic in size.
The Olympia oyster, Ostreola conchaphila, is the native oyster of the Pacific coast of North America from Alaska to Mexico. The name is derived from the important 19th-century oyster industry near Olympia, Washington, in Puget Sound. Native American peoples consumed O. conchaphila everywhere it was found, with consumption in San Francisco Bay so intense, enormous middens of oyster shells were piled over thousands of years. One of the largest such mounds, the Emeryville Shellmound, near the mouth of Temescal Creek and the eastern end of the San Francisco – Oakland Bay Bridge, is now buried under the Bay Street shopping center. O. conchaphila nearly disappeared from San Francisco Bay following overharvest during the California Gold Rush (1848-50s) and massive silting from hydraulic mining in California's Sierra Nevada (1850s-1880s). California's most valuable fishery from the 1880s-1910s was based on imported Atlantic oysters, not the absent native. But in the 1990s, O. conchaphila once again appeared in San Francisco Bay near the Chevron Richmond Refinery in Richmond, California. Species restoration projects for the Olympia oyster funded by the US Government are active in Puget Sound and San Francisco Bay. An active restoration project is taking place in Liberty Bay, Washington. This Puget Sound location is the home of an old and new Olympia oyster population. Intertidal areas with native oyster populations or evidence of past populations are strong candidates for re-introduction. The re-establishment of the population is currently threatened by the invasive Japanese oyster drill Ocinabrina inorata. This species preys on the oysters by drilling a hole between the two valves and digesting the oyster's tissues. O. inorata is a threat to the oyster especially in areas with low populations of the mussel Mytilis. The Nature Conservancy of Oregon also has an ongoing restoration project at Netarts Bay, Oregon.
The southern mud oyster or native flat oyster, Ostrea angasi', is endemic to southern Australia, ranging from Western Australia to southeast New South Wales and around Tasmania. This species is found in sheltered, silty or sand-bottomed estuaries at depths between 1 and 30 m. Flat oysters, like all other oyster species, are filter feeders, feeding on, and taking in anything small enough to be filtered in their gills. This may include plankton, microalgae or inorganic material. The oyster industry in southern Australia has started farming O. angasi, after supplies of wild-caught individuals were exhausted due to overfishing.
Pseudoperna is a genus of extinct very small oysters. Pseudoperna live in tight groups. This small oyster is commonly found attached in groups to the shell of large species such as Inoceramus. Pycnodonte and Pseudoperna are preserved mostly as calcitic valves and are also found attached to Mytiloides.
Aquaculture Bivalves Oyster Seafood Ostreidae

Oyster farming is an aquaculture (or mariculture) practice in which oysters are raised for human consumption. Oyster farming most likely developed in tandem with pearl farming, a similar practice in which oysters are farmed for the purpose of developing pearls. It was practiced by the ancient Romans as early as the 1st century BC on the Italian peninsula and later in Britain for export to Rome. The French oyster industry has relied on aquacultured oysters since the late 18th century.

Commonly farmed food oysters include the Eastern oyster Crassostrea virginica, the Pacific oyster Crassostrea gigas, Belon oyster Ostrea edulis, the Sydney rock oyster Saccostrea glomerata, and the Southern mud oyster Ostrea angasi.

Ostrea lurida is a species of oyster that occurs on the Pacific coast of North America. This bivalve is approximately 6 to 8 centimetres (2.4 to 3.1 in) in length. The shell can be rounded or elongated and is white to purplish black and may be striped with yellow or brown. Unlike most bivalves, the Olympia oyster's shell lacks the periostracum, which is the outermost coating of shell that prevents erosion of the underlying shell. The color of the oyster's flesh is white to a light olive green. Ostrea lurida lie with their left valve on the substrate, where they are firmly attached. Unlike most bivalves, the oyster does not have a foot in adulthood. They also lack an anterior adductor muscle and do not secrete byssal threads, like mussels do. Olympia oysters, like other bivalves are filter feeders. This means that they filter their surrounding water and screen out the phytoplankton they feed on. Olympia's filter between 9 to 12 quarts of water each day. This is an essential function to keeping marine waters clean. Their beds also provide shelter for anemones, crabs, and other small marine life. This species has been recovered in archaeological excavations along the Central California coast of the Pacific Ocean, demonstrating it was a marine species exploited by the Native American Chumash people.

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