Oyster

Oysters are a special kind of sea creature called bivalve molluscs that live in salty or partly salty water. They have two shells that clamp together, and some kinds have very hard, chalky shells. Oysters come in many shapes, and not all of them look the same.

People in many places enjoy eating oysters because they taste delicious. Some oysters, called pearl oysters, make beautiful pearls that people collect and use for jewelry. Other kinds of oysters, like the clear windowpane oysters, are valued for their pretty shells.

Etymology

The word oyster comes from Old French oistre. It first appeared in English during the 14th century. The French word came from the Latin ostrea, which is the feminine form of ostreum. This Latin word is based on the Ancient Greek word ὄστρεον (ostreon), meaning 'oyster'. It is related to the Greek word ὀστέον (osteon), meaning 'bone'.

Types

True oysters

True oysters belong to the family Ostreidae. This family includes edible oysters from genera like Ostrea, Crassostrea, Magallana, and Saccostrea. Well-known examples are the European flat oyster, eastern oyster, Olympia oyster, Pacific oyster, and the Sydney rock oyster. These oysters began appearing in the Early Triassic epoch.

Pearl oysters

Main article: Pearl oyster

Most shell-bearing mollusks can make pearls, but many are not very valuable. Pearls can form in both saltwater and freshwater.

Pearl oysters are different from true oysters and belong to the family feathered oysters (Pteriidae). Both cultured pearls and natural pearls come from pearl oysters, but other mollusks, like freshwater mussels, can also make valuable pearls.

The largest pearl-making oyster is Pinctada maxima, about the size of a dinner plate. Not every oyster makes pearls.

In nature, pearl oysters make pearls by covering a tiny irritating object with nacre. Over time, layers of nacre turn the irritant into a pearl. The many types, colors, and shapes of pearls depend on the natural pigment of the nacre and the shape of the original irritant.

Pearl farmers can help make a pearl by putting a nucleus, often a piece of polished mussel shell, inside the oyster. In three to seven years, the oyster can make a perfect pearl. Since the early 1900s, when people learned how to make artificial pearls, the market for cultured pearls has grown much larger than the market for natural pearls.

Other types

Some bivalve mollusks, besides true oysters and pearl oysters, have names that include "oyster" because they taste or look like true oysters or make noticeable pearls. Examples are:

• Thorny oysters in the genus Spondylus
• Pilgrim oyster, another name for a scallop, after the scallop shell of St. James
• Saddle oysters, members of the Anomiidae family also called jingle shells
• Dimydarian oysters, members of the Dimyidae family
• Windowpane oysters

In the Philippines, a local thorny oyster called Tikod amo is a popular seafood in the southern part of the country. It tastes great and costs a lot.

Anatomy

Oysters breathe using their gills. They can also take in and release air through their mantles, which have many tiny blood vessels. A small heart under the adductor muscle moves blood around their body. Two kidneys help clean the blood by taking out waste.

Some oysters can have both eggs and sperm in their reproductive organs. After the eggs are joined with sperm, the female oyster releases them into the water. The tiny baby oysters, called veliger larvae, float in the water for a few weeks before they settle down and grow up.

Feeding

Oysters are filter feeders, which means they take in water through their gills using tiny hair-like structures called cilia. They catch tiny plants and other small particles floating in the water, trap them in mucus on their gills, and then move them to their mouths to eat. After eating, they either digest the food or push out bits that they cannot use, which fall to the ocean floor.

Oysters like to eat when the water is warm, between about 20–26 °C (high 60s to high 70s in Fahrenheit). In perfect lab conditions, one oyster can clean up to 190 liters (about 50 gallons) of water each day. Normally, a mature oyster can clean between 11 and 45 liters (3 to 12 gallons) of water each day. In the past, the many oysters in Chesapeake Bay could clean all the water there every few days, but now it takes much longer.

Habitat and behaviour

A group of oysters is called a bed or oyster reef. Oysters are filter feeders, which means they take in water to eat and breathe, but they do not stay open all the time. They close their shells to rest, even when they are always underwater. Their actions follow the patterns of the moon and sun.

Oysters live in coastal waters all around the world. They help keep the water clean by eating tiny plants and particles. Oyster reefs give homes to fish and small sea animals and protect shores from erosion. Oysters are important for both nature and people, giving us food and nutrients. However, they face problems like diseases and changes in their environment.

As a important species, oysters give homes to many sea creatures. Some oysters live in areas that are sometimes underwater and sometimes above water, while others live deeper in the water. The hard shells of oysters and the spaces between them become homes for many small animals, like sea anemones, barnacles, and hooked mussels. These small animals are food for bigger animals, such as fish like striped bass, black drum, and croakers.

An oyster reef can make a flat bottom ten times bigger in surface area. The shape of an oyster depends on where it first attaches, but it always points its outer shell upward. One side of the shell is cupped, and the other is flat.

Oysters usually become adults in one year. In their first year, they release sperm into the water. Later, as they grow bigger, they release eggs. In places like bays, oysters usually release their eggs and sperm from late June to mid-August. When the water gets warmer, a few oysters start this process, which causes many others to do the same, filling the water with eggs and sperm. One female oyster can make up to 100 million eggs each year. The eggs meet the sperm in the water and grow into larvae, which settle on surfaces like oyster shells. These young oysters are called spat. Many oysters like to settle near other oysters.

Some tropical oysters grow best on mangrove roots. During low tide, they can be easily collected.

The largest area for oyster production in the United States is the Chesapeake Bay, though there are fewer oysters there now because of overfishing and pollution. Other big areas for oyster farming in the US are along the coast of the Gulf of Mexico, from Apalachicola, Florida to Galveston, Texas. Japan and Australia also have large oyster beds. In 2005, China produced 80% of the world's oysters. In Europe, France leads in oyster farming.

Oysters are eaten by crabs, seabirds, starfish, and humans. Some oysters have small crabs living inside them, called oyster crabs.

Nutrient cycling

Oysters are a type of bivalve that help keep water clean. They eat tiny plants and animals, as well as bits of organic material, from the water. This process helps make the water clearer and can improve its quality.

In places like Maryland, people have used oysters to help reduce harmful substances in the water. One acre of oysters can clean a lot of water every day. This not only helps the environment but can also create jobs and bring in money for local communities.

Ecosystem services

Oysters play an important role in nature. They help keep water clean by filtering it and can support many other plants and animals. Oyster reefs also protect shorelines from strong waves and storms. When oysters grow together, they create habitats where many sea creatures can live. Because of these benefits, people are working to protect and restore oyster reefs.

Human history

Oysters have been an important food source for humans for thousands of years. Ancient people left behind piles of oyster shells, called middens, showing they ate oysters long ago. In places like Japan, people have been growing oysters since at least 2000 BC. In the United Kingdom, a town called Whitstable is famous for its oyster farming, which has been happening since Roman times.

In Victorian England, people enjoyed eating oysters with beer, especially a type called oyster stout. Brewers discovered that adding crushed oyster shells to beer helped to make it clearer. This idea started in 1938 in London.

Oysters were once very cheap and were mainly eaten by working people. In the 19th century, New York City had huge oyster beds. Millions of oysters were sold every day, and they helped start the city’s restaurant business. However, over time, many of these oyster beds were destroyed, and today oysters are more expensive and considered a special treat.

In Britain, local oysters take five years to grow and are protected during their spawning season. Now, larger types of oysters from the Pacific and Rock species are commonly farmed all year round.

Oysters are collected from the wild in different ways. In shallow water, people can pick them up by hand or with small tools. In deeper water, special tools like rakes or tongs are used. Some areas use a tool called a scallop dredge, which is pulled through the water by a boat to collect oysters. However, this can damage the oyster beds, so its use is carefully controlled.

Oysters can also be collected by divers who swim down to pick them up. After collecting, the oysters are sorted to remove any that are dead or unwanted before they are sold.

Oysters have been farmed since Roman times. Today, the Pacific oyster is the most commonly farmed type. There are two main ways to farm oysters: release and bagging. Both methods start by growing baby oysters, called spat, on land. Then they are placed in the water to grow bigger. The release method lets them grow naturally in existing oyster beds, while the bagging method keeps them in racks or bags above the bottom to protect them from predators.

Farming oysters in the water where fish or prawns are also raised can help feed the oysters, as the extra food from the fish ponds supports tiny plants that the oysters eat.

To prevent farmed oysters from spreading to new areas, special sterile oysters are created by mixing different types of oysters. These sterile oysters cannot have babies, so they don’t change wild oyster populations.

In some places, new types of oysters have been added to help increase oyster numbers. For example, the Pacific oyster was introduced to areas like Pendrell Sound, where it has become a big part of the local oyster industry.

Efforts to restore oyster reefs have helped bring back some oyster populations. For example, in the Chesapeake Bay, scientists built special reefs to support native oysters. These reefs now home millions of oysters, though this is still far less than in the past.

Projects using oysters to clean water and protect coastlines have shown promise. By placing oyster reefs in certain areas, they can help filter water and reduce waves, protecting shorelines. However, some places have concerns about using oysters for this purpose, especially where people might ignore warnings and eat oysters that could be unsafe.

Oyster reef restoration also helps protect ocean life and can support efforts to fight the effects of climate change on coastlines.

The introduction of new oyster species by humans can sometimes harm local oyster populations. For example, in Tomales Bay, new species caused a big drop in the number of native oysters.

Oysters can also be affected by underwater noise from ships, construction, and other human activities. These sounds can change how oysters behave and affect their ability to reproduce.

Changes in the environment due to things like climate change are also making life harder for oysters around the world, affecting their health and behavior.

Recycling oyster shells helps restore oyster reefs, which provide homes for marine life and protect shorelines from storms. Many places collect used shells from restaurants to help rebuild reefs. For example, the Billion Oyster Project in New York aims to return one billion oysters to the harbor by getting people involved in shell recycling.

Efforts to rebuild oyster reefs have received funding to support recycling programs in many states. These projects help protect coastal areas and support local wildlife.

Historically, oyster shells were used in a special type of building material called tabby concrete, made from burnt shells and broken pieces. This material was used in many old buildings along the Atlantic coast.

As food

People have been eating oysters for a very long time. There is proof of this from places all over the world where people collected lots of oyster shells. Oysters have been a popular food along coastlines wherever they can be found, and places where they grow a lot have often built up a business around catching them. Even though there are now fewer oysters because of fishing too much and problems like diseases and pollution, they are still enjoyed by many people and celebrated at special oyster festivals in many towns and cities.

There used to be a belief that oysters were only safe to eat in months that have the letter “r” in them. This idea came from the fact that in warmer months, like May, June, July, and August, oysters can spoil more easily. Recently, some harmful germs have been found in oysters during these summer months, which helps explain why this belief exists.

Oysters can be eaten in many different ways. They can be served on the half shell, raw, smoked, boiled, baked, fried, roasted, stewed, canned, pickled, steamed, or broiled. Sometimes they are used in drinks or dishes like Oysters Rockefeller. When eating them raw, people often add butter, salt, or lemon juice. Some fancy restaurants serve them with a special mix of shallot, peppercorn, white wine, and lemon juice called mignonette sauce. Oysters taste different depending on where they come from — they can be salty, briny, buttery, metallic, or fruity, and they have a soft, fleshy texture.

Oysters are also good for you because they have lots of important nutrients like zinc, iron, calcium, selenium, vitamin A, and vitamin B₁₂. They are low in calories — eating a dozen raw oysters only gives you about 110 calories. Oysters also have protein and are a good source of zinc and vitamin B₁₂.

Opening oysters can be tricky. There are special knives made just for this, and it’s important to be careful because the shell can be very sharp. There are competitions where people try to open oysters as fast as they can!

Diseases

Oysters can get sick from different diseases, which can make it hard for farmers to grow them and can reduce the number of oysters in some places. Scientists work hard to stop these diseases and create oysters that are stronger against them.

One disease called "Dermo" is caused by a tiny creature called Perkinsus marinus. It can make many oysters die and hurt the oyster business, but it does not make people sick if they eat infected oysters. It started in the Gulf of Mexico in the 1950s and has slowly moved up the east coast of the United States.

Another disease, called MSX, is caused by a tiny creature named Haplosporidium nelsoni. It can also make many oysters die, but the ones that survive can become stronger. This disease was first found in Delaware Bay in 1957 and is now found along the East Coast of the United States.

Some oysters can also carry bacteria that might make people sick, like Vibrio vulnificus. This can cause stomach problems and skin infections, which usually need a doctor’s help to get better.