Oysters are a type of shellfish that live in brackish and saltwater bays, estuaries, and tidal creeks. Once oyster larvae attach to a surface, such as other oyster shells, they are known as spat, As generation after generation of spat grow into adult oysters, they form dense clusters known as oyster reefs or beds.
Oysters are bivalve mollusks, with a hinged shell, like mussels, clams and scallops they. Adults are sessile — they stay in one place — and inhabit both intertidal and subtidal areas. They have fast growth rates and high reproduction rates. and often form clusters or beds among long, green eelgrass in muddy water.
Oysters are found in coastal areas in tropical and temperate oceans. They often are found in places where freshwater mixes with seawater. There are hundreds of different species of them, including thorny oysters whose shells are covered with pines and often algae, which is used as camouflage; and saddle oysters which affix themselves to surfaces using glue secreted from a hole in the bottom of their shells.
Oysters play a key roll in filtering the water to keep it clean. As filter feeders, they remove stuff floating around in the water. Cleaner water helps promote the growth of underwater grasses, such as wild celery, which serve as important habitat for other species. In addition, oyster beds form large, complex structures where many aquatic species, such as fish and crabs, hunt for food and hide from predators. Oyster are vulnerable to attack from a number of different predators including starfish, sea snails and man. They are also hurt by pollution and struck by diseases that kill of millions of them.
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems
Pearls are produced by oysters as everyone knows. They are composed of 90 percent argonite calcium carbonate, a substance applied to a nucleus of pearl by the same organ (the mantle) of the oyster that creates the shell, and 10 percent conchiolin, a gluelike protein that binds together the calcium carbonate crystals. Fossil pearls are abundant in 60 million-year-old rocks. [Source: Fred Ward, National Geographic, August 1985 ┦; David Doubilet, National Geographic, December 1991; Nigel Sitwell, Smithsonian]
Calcium carbonate is the material from which cement and limestone are made and argon is an inert gas like neon. This nacre is applied in layers about a thousandth of an inch thick. The growth pattern makes cultured and natural pearls feel rough when rubbed on the teeth. One advantage pearls have over gem stones and gold is that didn't require any cutting or smelting. They came straight from the shell ready to go. This was especially important to ancient people didn't the have the technology we have today to cut stone and produce metal.
It is said that pearls form inside shellfish that have foreign object inside them that is an irritant. It is speculated that the objects causes pain and covering it with nacre makes it smoother and less irritating.
Oysters as Food and Aphrodisiacs
Edible oysters are one of the mostly widely consumed mollusks and have been consumed since ancient times. Consumer are advised to eat farmed oysters. Oysters from the sea or bays are usually harvested with vacuum-cleaner-like dredges that destroy sea floor habitats.
In Japan, some seafood restaurants serves “apapa” (oysters cooked live on grill that go "apapa" when they pop open); The Japanese love oysters. One of the first places that many Japanese seek out during trips to the United States is a restaurant with a oyster bar that offers raw oysters. A Japanese man who died at the age of 96 before he died said he owed his long life to the fact he swallowed two oysters every morning.
Casanova once attributed his lovemaking prowess to his daily breakfast of 50 oysters. He called oysters "a spur to the spirit and to love." One of the juicier passages in his autobiography is a description of something called the oyster game, in which he and the women he was trying to seduce would try to eat oysters off each other tongue.
Pacific oysters (Scientific name: Crassostrea gigas) are also known as Japanese oysters, Miyagi oysters and Pacific cupped oysters. They can reach up to 25 centimeters (10 inches) in length. The shell is gray, elongated, thick, rough and sometimes sharp. The inside of the shell is white to off/white with purple streaks. The shell has a “cupped” shape to it, giving rise to its alternate name “Pacific cupped oyster.” The Pacific oyster can found growing naturally and in farms in Japan and elsewhere in East Asia. In the U.S. they can be found off West Coast. Cluster of these oysters grow well among long, green eelgrass in somewhat murky water. Oyster first mature as males, then later develop female reproductive capabilities. Each female can produce between 50 and 200 million eggs during a spawning event.. [Source: NOAA]
Eastern oysters (Scientific name: Crassostrea virginica) are also known as American oysters, Atlantic oysters, American cupped oysters and Virginia oysters. They average 7.5 to 12.5 centimeters (3–5 inches) in length and can grow up to 20 centimeters (8 inches) in length. Their lifespan is up to 20 years. Eastern oysters are found along eastern North America from the Gulf of St. Lawrence to the Gulf of Mexico. They are associated with the middle and lower Chesapeake Bay and its rivers and are the only species of oyster native to this region. [Source: NOAA]
Eastern oysters are treasured as food by humans and other species. They live in brackish and salty waters at depths from 25 to 110 meters (8 to 35 feet). In some warmer areas, they are able to live in the intertidal zone. They attach to firm bottom areas and to each other to grow into beds or reefs. These reefs provide habitat for fish, crabs, invertebrates, macrofauna, and birds.. As filter feeders, they help filter the water. The beige-colored Eastern oyster shell has smooth edges and is oval in shape. The inside of the shell is white to off-white to brownish in color. The shell has a “cupped” shape to it, giving rise to its alternate name “American cupped oyster.”
Pearl oysters belong to the genus Pinctada, within the oyster family Pteriidae. They have a strong inner shell layer composed of nacre — "mother of pearl" — and are not closely related to either the edible oysters of family Ostreidae or the freshwater pearl mussels of the families Unionidae and Margaritiferidae. Pinctada margaritifera and P. maxima are used for culturing South Sea and Tahitian pearls. [Source: Wikipedia]
All species within the genus Pinctada, produce pearls. Attempts have been made to harvest pearls commercially from many Pinctada species. However, the ones listed below are only species that are currently producing significant, commercially-viable quantities of pearls are: 1) Gulf pearl oyster (Pinctada radiata), found in the Persian Gulf, Red Sea, Mediterranean Sea and throughout the Indo-Pacific as far as Japan and Australia. 2) Black-lip oyster (Pinctada margaritifera), found in the Persian Gulf and southwestern part of Indian Ocean; Fiji; Tahiti; Myanmar; Baja California; Gulf of Mexico 3) Gold-lip oyster (Pinctada maxima), found in Australia; Fiji; Tahiti 4) White-lip oyster (Pinctada maxima), found in Australia; Fiji; Tahiti; and Myanmar Pinctada mazatlanica; Mexico; Panama 5) Akoya pearl oyster (Pinctada fucata, also called P. martensii), found in the Red Sea; Sri Lanka; Persian Gulf; Indian Ocean; Western Pacific Ocean; Australia; China; Venezuela 6) Shark Bay pearl oyster (Pinctada albina), found in Australia.
Black-lip pearl oysters (Scientific name: Pinctada margaritifera) are main marine pearl-bearing oysters. They are found over a wide geographic range extending from Baja California across the Indo-Pacific basin to the Red Sea, and northwards into the Eastern Mediterranean Sea. These regions enclose a number of suitable habitats for the oyster that feature coral reefs and lagoons. There are seven subspecies of Black-lip pearl oyster; each has a particular local distribution within the range of the species: 1) typica: Ryukyus in Japan, Taiwan, Australia, Micronesia and Melanesia; 2) cumingi: Cook Islands, French Polynesia; 3) mazalanica: Panama Bay, Baja California; 4) erythraensis: Red Sea; 5) persica: Persian Gulf; 6) zanzibarensis: East Africa, Madagascar, and the Seychelle Islands; and 7) galtsoffi: Hawaiian Archipelago. [Source: Albert Gamez, Animal Diversity Web (ADW) /=]
Oyster Characteristics, Behavior and Feeding
Oysters are epifaunal, meaning they live aggregates of animals at the bottom of the ocean. They use byssal threads (strong, silky fibers made from proteins used by bivalves to attach to surfaces) to cement their left hand valve directly onto surfaces such as rocks, other oysters, mangrove roots, pilings, shells of other animals and other substrates and hard surfaces. [Source: Albert Gamez, Animal Diversity Web (ADW) /=]
Oysters are cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature), heterothermic (have a body temperature that fluctuates with the surrounding environment) and have bilateral symmetry (both sides of the animal are the same). They are diurnal (active during the daytime), nocturnal (active at night), crepuscular (active at dawn and dusk), sessile (fixed in one place) and sedentary (remain in the same area). Oysters sense and communicate with chemicals usually detected by smelling or smelling-like senses.
Black-lip pearl oysters range in weight from 5.5 to 8.8 grams (0.19 to 0.31 ounces) and have a maximum lengths of 14.6 centimeters (5.75 inches), with their average length being 13 centimeters millimeters (5.12 inches). Sexual Dimorphism (differences between males and females) is minimal: Both sexes are roughly equal in size and look similar. Black-lip pearl oyster shells are black with a black, non-nacreous border, and is one of the largest species in its genus.
Oysters are primarily planktivores, feeding on zooplankton (animal plankton) and phytoplankton (plant plankton). They are nonselective filters feeder that feeds mainly on plankton that floats into their gills. Studies of black-lip pearl oyster have found mud, inorganic materials, and other less than ideal items within their digestive tract. (Sims, 1993) /=\
Oyster Mating and Reproduction
Female oysters lay millions of eggs. Males release their sperms which mixes with the eggs in the open water. A fertilized egg produces a swimming larvae in 5 to 10 hours. Only around one in four million larvae make it to adult hood. Those that survive for two weeks attach themselves to something hard and begin growing and begin developing into oysters. When oysters reproduce, they spawn tiny larvae that freely navigate the water column until they find an appropriate habitat with a structure to settle on. Once the larvae permanently attach to a surface, they are known as spat.
Oysters are oviparous (young are hatched from eggs) and iteroparous (offspring are produced in groups). Reproduction is external, meaning the male’s sperm fertilizes the female’s egg outside her body. They employ broadcast (group) spawning, the main mode of reproduction in the sea. It involves the release of both eggs and sperm into the water and contact between sperm and egg and fertilization occur externally. Many oysters are sequential hermaphrodites (individuals change their sex at some point in their lives and typically produces eggs and sperm at different stages their lives) and and protandrous (the condition of hermaphrodites that have male organs and sperm before female organs and eggs). [Source: Albert Gamez, Animal Diversity Web (ADW) /=]
Black pearl oysters engage in seasonal breeding and may spawn several times during their breeding season. Depending on their geographic location, black pearl oysters may spawn anytime between March to November. As broadcast spawners, there is no parental investment . Young develop independently in the water column, drifting as plankton. Their life cycle is characterized by metamorphosis — a process of development in which individuals change in shape or structure as they grow. /=\
Black-lip pearl oysters are protandrous hermaphrodites. They begins life as a males and later changes into a female. Black-lip pearl oyster reaches sexual maturity around two years of age which is also around the same time the animal changes its sex. Spawning is dependent on a number of factors, including salinity, currents, air exposure, and temperature. According to Animal Diversity Web: Oysters in temperate regions show more distinct seasonality in spawning, while tropical oysters have more of a year-round, intermittent schedule. Timing of spawning varies greatly from region to region. In the Red Sea, spawning occurs from March through September. However, there are two spawning seasons in Australia, one between July to August, and one in November. [Source: Albert Gamez, Animal Diversity Web (ADW) /=]
The larval stage of Black-lip pearl oyster can last for 16 to 30 days with an average daily growth rate of 3.7 to 5 micrometers; development time is largely dependent on factors such as temperature and nutrition. The planktonic larva is known as a veliger, which develops a type of swimming mechanism called a ciliated velum also used for food transfer. At some point, the veliger will grow an appendage used to move across hard surfaces. After settlement as a postlarva, these oysters spend a large amount of time seeking a compatible substrate (usually in a dark area) to bind to with its byssal threads. If such a substrate cannot be found, the oyster will migrate to a different location using its foot. Within the first two years of life, the shell may grow between 100 to 120 millimeters. At two years of age, the oyster has matured into an adult capable of reproducing.
Oyster Ecological Roles and Predators
Ecologically, oysters and other bivalves play an important role influencing phytoplankton concentrations through “top-down” grazer control. According to Animal Diversity Web: This action reduces particle density within the water and increases the amount of light which can reach benthic (bottom-dwelling) organisms. Bivalve waste can be assimilated as food for phytoplankton growth. Furthermore, the oyster beds form a sheltering hard-substrate habitat, housing numerous invertebrate species, and the oysters themselves are food for higher-order carnivores (animals that mainly eat meat or animal parts). [Source: Albert Gamez, Animal Diversity Web (ADW) /=]
Despite the protection of their shells, oysters are vulnerable to predation by sharks, rays, ctopus, starfish and predatory gastropods. The gastropod virgin murex (Chicoreus virgineus) is described as the most dangerous predator for unprotected black-lip pearl oysters within the Red Sea. Mud worms were responsible for the majority of deaths of this species in Palau. Pearl oysters are most vulnerable as larvae, because they are eaten by planktivores and are easily swept away from desirable benthic (bottom-dwelling) areas by ocean currents.
Japan Scientists Study Oyster 'Language'
Scientists in Japan have studied the "language" of oysters in an effort to find out what they are saying about their environment. AFP reported: Researchers are monitoring the opening and closing of the molluscs in response to changes in seawater, such as reduced oxygen or red tide, a suffocating algal bloom, that can lead to mass die-offs. Using a device they have nicknamed the "kai-lingual", a play on the Japanese word "kai" or shellfish, scientists from Kagawa University want to see if they can decode oyster movements that might warn of possible problems. [Source: AFP, December 6, 2011]
The "kai-lingual" uses a series of sensors and magnets to send information on the opening and closing of shells in response to environmental changes. The technique has never before been used on oysters farmed for food, but has been employed by pearl oyster farmers. "With kai-lingual, we can hear the 'screams', like 'we are in pain because of insufficient oxygen'," said Tsuneo Honjo, director of the Seto Inland Sea Regional Research Center at the university.
Pearl oysters have been placed among their food-farmed cousins where they have acted as "interpreters", alerting growers to ocean changes, he said. "We have firmly established conversations with pearl oysters through years of research. They should translate into the reactions of the farmed oysters for us in this project," he said. "So far, oysters are talking in a healthy fashion."
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated April 2023