Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species the valves are calcified, many are somewhat irregular in shape. Many, but not all, oysters are in the superfamily Ostreoidea; some kinds of oysters are consumed cooked or raw and are regarded as a delicacy. Some kinds of pearl oysters are harvested for the pearl produced within the mantle. Windowpane oysters are harvested for their translucent shells, which are used to make various kinds of decorative objects. 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, the latinisation of the Greek ὄστρεον, "oyster". Compare ὀστέον, "bone". True oysters are members of the family Ostreidae; this family includes the edible oysters, which belong to the genera Ostrea, Ostreola and Saccostrea. Examples include the Belon oyster, eastern oyster, Olympia oyster, Pacific oyster, the Sydney rock oyster.
All shell-bearing mollusks can secrete pearls, yet most are not valuable. Pearls can form in both freshwater environments. Pearl oysters are not related to true oysters, being members of a distinct family, the feathered oysters. Both cultured pearls and natural pearls can be extracted from pearl oysters, though other molluscs, such as the freshwater mussels yield pearls of commercial value; the largest pearl-bearing oyster is the marine Pinctada maxima, the size of a dinner plate. Not all individual oysters produce pearls naturally. In fact, in a harvest of two and a half tons of oysters, only three to four oysters produce what commercial buyers consider to be absolute perfect pearls. In nature, pearl oysters produce pearls by covering a minute invasive object with nacre. Over the years, the irritating object is covered with enough layers of nacre to become a pearl; the many different types and shapes of pearls depend on the natural pigment of the nacre, the shape of the original irritant. Pearl farmers can culture a pearl by placing a nucleus a piece of polished mussel shell, inside the oyster.
In three to seven years, the oyster can produce a perfect pearl. These pearls are not as valuable as natural pearls, but look 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 have common names that include the word "oyster" because they either taste like or look somewhat like true oysters, or because they yield noticeable pearls. Examples include: Thorny oysters in the genus Spondylus Pilgrim oyster, another term for a scallop, in reference to the scallop shell of St. James Saddle oysters, members of the Anomiidae family known as jingle shells Dimydarian oysters, members of the family Dimyidae Windowpane oysters In the Philippines, a local thorny oyster species known as Tikod Amo is a favorite seafood source in the southern part of the country; because of its good flavor, it commands high prices. Oysters are filter feeders.
Suspended plankton and particles are trapped in the mucus of a gill, from there are transported to the mouth, where they are eaten and expelled as feces or pseudofeces. Oysters feed most at temperatures above 10 °C. An oyster can filter up to 5 L of water per hour; the Chesapeake Bay's once-flourishing oyster population filtered excess nutrients from the estuary's entire water volume every three to four days. Today, that would take nearly a year. Excess sediment 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 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, their nervous system includes three pairs of ganglia. While some oysters have two sexes, their reproductive organs contain sperm.
Because of this, it is technically possible for an oyster to fertilize its own eggs. The gonads surround the digestive organs, are made up of sex cells, branching tubules, connective tissue. Once the female is fertilized, she discharges millions of eggs into the water; the larvae develop in about six hours and exist suspended in the water column as veliger larvae for two to three weeks before settling on a bed and maturing to sexual adulthood within a year. A group of oysters is called a bed or oyster reef; as a keystone species, oysters provide habitat for many marine species. Crassostrea and Saccostrea live 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 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 depends on the type of bottom to which it is attached, but it always orients itself with its outer, flared shell tilted upward. One valve is cupped and t
A wetland is a distinct ecosystem, inundated by water, either permanently or seasonally, where oxygen-free processes prevail. The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique hydric soil. Wetlands play a number of functions, including water purification, water storage, processing of carbon and other nutrients, stabilization of shorelines, support of plants and animals. Wetlands are considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life. Whether any individual wetland performs these functions, the degree to which it performs them, depends on characteristics of that wetland and the lands and waters near it. Methods for assessing these functions, wetland ecological health, general wetland condition have been developed in many regions and have contributed to wetland conservation by raising public awareness of the functions and the ecosystem services some wetlands provide.
Wetlands occur on every continent. The main wetland types are swamp, marsh and fen. Many peatlands are wetlands; the water in wetlands is either brackish, or saltwater. Wetlands can be non-tidal; the largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, the Sundarbans in the Ganges-Brahmaputra delta. The UN Millennium Ecosystem Assessment determined that environmental degradation is more prominent within wetland systems than any other ecosystem on Earth. Constructed wetlands are used to treat municipal and industrial wastewater as well as stormwater runoff, they may play a role in water-sensitive urban design. A patch of land that develops pools of water after a rain storm would not be considered a "wetland" though the land is wet. Wetlands have unique characteristics: they are distinguished from other water bodies or landforms based on their water level and on the types of plants that live within them. Wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants.
A more concise definition is a community composed of hydric soil and hydrophytes. Wetlands have been described as ecotones, providing a transition between dry land and water bodies. Mitsch and Gosselink write that wetlands exist "...at the interface between terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet dependent on both."In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions. A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota rooted plants, to adapt to flooding." There are four main kinds of wetlands – marsh, swamp and fen. Some experts recognize wet meadows and aquatic ecosystems as additional wetland types; the largest wetlands in the world include the swamp forests of the Amazon and the peatlands of Siberia. Under the Ramsar international wetland conservation treaty, wetlands are defined as follows: Article 1.1: "...wetlands are areas of marsh, peatland or water, whether natural or artificial, permanent or temporary, with water, static or flowing, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres."
Article 2.1: " may incorporate riparian and coastal zones adjacent to the wetlands, islands or bodies of marine water deeper than six metres at low tide lying within the wetlands." Although the general definition given above applies around the world, each county and region tends to have its own definition for legal purposes. In the United States, wetlands are defined as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, that under normal circumstances do support, a prevalence of vegetation adapted for life in saturated soil conditions. Wetlands include swamps, marshes and similar areas"; this definition has been used in the enforcement of the Clean Water Act. Some US states, such as Massachusetts and New York, have separate definitions that may differ from the federal government's. In the United States Code, the term wetland is defined "as land that has a predominance of hydric soils, is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation adapted for life in saturated soil conditions and under normal circumstances supports a prevalence of such vegetation."
Related to this legal definitions, the term "normal circumstances" are conditions expected to occur during the wet portion of the growing season under normal climatic conditions, in the absence of significant disturbance. It is not uncommon for a wetland to be dry for long portions of the growing season. Wetlands can be dry during the dry season and abnormally dry periods during the wet season, but under normal environmental conditions the soils in a wetland will be saturated to the surface or inundated such that the soils become anaerobic, those conditions will persist through the wet portion of the growing season; the most important factor producing wetlands is flooding. The duration of flooding or prolonged soil saturation by groundwater determines whether the resulting wetland has aquatic, marsh or swamp vegetation
Petersburg National Battlefield
Petersburg National Battlefield is a National Park Service unit preserving sites related to the American Civil War Siege of Petersburg. The Battlefield is centered on the city of Petersburg and includes outlying components in Hopewell, Prince George County, Dinwiddie County. Over 140,000 people visit the park annually. Petersburg National Battlefield is composed of three major units and an additional managed component. Located off Virginia Route 36 east of Petersburg, the Eastern Front Visitor Center is the main visitor contact station for the Battlefield. Here, visitors can view exhibits and movies about the Siege of Petersburg as well as view Battery #5, an important early site in the Siege; the park entrance fee is collected on the Eastern Front Visitor Center access road. After leaving the Visitor Center, one can begin their park tour. A motor tour route runs from Virginia Route 36 to US Route 301. Along the way, visitors can view sites such as The Crater. Located in Dinwiddie County about 14 miles southwest of downtown Petersburg, this unit contains the site of the Battle of Five Forks, which destroyed a sizable portion of the remaining Confederate Army of Northern Virginia.
Sometimes called the "Waterloo of the Confederacy," Five Forks helped set in motion a series of events that led to Robert E. Lee's subsequent surrender at Appomattox Court House. Sited next to the James River in Hopewell, City Point served as a major command and logistics hub for the Union Army during the Siege of Petersburg, it is located in the City Point Historic District. The 8.72-acre Poplar Grove National Cemetery is administered by Petersburg National Battlefield. Established as Petersburg National Military Park on 1926-07-03. Transferred from the War Department on 1933-08-10. Redesignated as Petersburg National Battlefield on 1962-08-24. Added to the National Register of Historic Places on 1966-10-15. Richmond National Battlefield Park, administering areas related to the Siege of Petersburg which are north of the James River and Appomattox River; the National Parks: Index 2001-2003. Washington: U. S. Department of the Interior. Official NPS website: Petersburg National Battlefield
Mission-Aransas National Estuarine Research Reserve
The Mission-Aransas National Estuarine Research Reserve is a large contiguous complex of wetland and marine environments on the Texas Coastal Bend in the United States. Named for the two major rivers that flow into the area, the reserve contains public and private lands and waters; the land is coastal prairie with unique oak motte habitats. The wetlands include riparian habitat, freshwater marshes, saltwater marshes. Within the water areas, the bays are large and include extensive tidal flats, seagrass meadows and oyster reefs; these unique and diverse estuarine habitats in the western Gulf of Mexico support a host of endangered and threatened species including the endangered whooping crane. Traditional activities within the proposed reserve include boating, hunting and gas extraction, shellfish harvesting and recreational activities. Despite a long history of human uses and its close proximity to the city of Corpus Christi, the reserve is rural and pristine; the University of Texas Marine Science Institute operates locations for visitors to learn about and explore the reserve.
University of Texas Marine Science Institute Visitor Center - located in Port Aransas, features seven aquaria representing typical Texas coastal habitats, self guided tours and educational movies. The facility includes a gift shop. Wetlands Education Center- located in Port Aransas, an artificial wetlands seagrass pond that occupies 3.5 acres between the MSI Visitors Center and the South Jetty. Visitors can tour a boardwalk around the pond to view the vegetation and the wildlife, view educational signage. Bay Education Center - located in Rockport, features exhibits about the estuary's ecosystem and Science On a Sphere, a spherical display system created by NOAA to illustrate Earth science concepts. University of Texas Marine Science Institute - Visitor information This article incorporates public domain material from websites or documents of the NOAA
Elkhorn Slough National Estuarine Research Reserve
The Elkhorn Slough National Estuarine Research Reserve is one of 28 National Estuarine Research Reserves established nationwide as field laboratories for scientific research and estuarine education. Elkhorn Slough is located 100 miles south of San Francisco, California on the central shore of Monterey Bay; the Reserve is administered by the National Atmospheric Administration. It is managed as Elkhorn Slough Ecological Reserve by the California Department of Game; the Mission of the Elkhorn Slough National Estuarine Research Reserve is to ensure the perpetual health of ecosystems in Elkhorn Slough and the surrounding watershed through preservation, research, information exchange and education with particular emphasis on the Research Reserve. The 1,700-acre Reserve hosts programs that promote education and conservation in Elkhorn Slough; the award-winning visitor center has exhibits and is a trailhead for five miles of trails that meander through oak woodlands, calm tidal creeks, freshwater marshes.
It is a popular spot for kayaking and birding. The Reserve's visitor center is located at 1700 Elkhorn Road, Watsonville, CA 95076. Elkhorn Slough National Estuarine Research Reserve - official website operated by the Elkhorn Slough Foundation Elkhorn Slough National Estuarine Research Reserve at the California Department of Fish and Wildlife Elkhorn Slough National Estuarine Research Reserve at the National Estuarine Research Reserve System
North Inlet-Winyah Bay National Estuarine Research Reserve
The North Inlet-Winyah Bay National Estuarine Research Reserve, in the U. S. State of South Carolina, features the salt marshes and ocean dominated tidal creeks of the North Inlet Estuary plus the brackish waters and marshes of the adjacent Winyah Bay Estuary. North Inlet is a pristine system in which water and habitat quality are much higher than those in Winyah Bay; as the estuary with the third largest watershed on the east coast, Winyah Bay has been influenced by agriculture and other human activities. More than 90 percent of North Inlet's watershed is in its natural forested state The reserve is home to many threatened and endangered species, including sea turtles, least terns and wood storks. Reserve resources range from tidal and transitional marshes to oyster reefs and inter-tidal flats and from coastal island forests to open waterways. "North Inlet-Winyah Bay National Estuarine Research Reserve". Www.northinlet.sc.edu. University of South Carolina. Retrieved November 13, 2018."North Inlet-Winyah Bay Reserve, South Carolina".
National Estuarine Research Reserve System. National Oceanic and Atmospheric Administration. March 31, 2004. Archived from the original on September 30, 2009; this article incorporates public domain material from websites or documents of the NOAA