Oyster

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

People in many places enjoy eating oysters because they taste delicious. Some oysters, called pearl oysters, make beautiful pearls. People collect these pearls to 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 entered English in the 14th century. The French word came from the Latin ostrea. 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.

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. They take in water through their gills using tiny hair-like structures called cilia. They catch tiny plants and small particles in the water. They trap these in mucus on their gills and move them to their mouths to eat. After eating, they either digest the food or push out bits they cannot use. These bits fall to the ocean floor.

Oysters like to eat when the water is warm, between about 20–26 °C. In perfect lab conditions, one oyster can clean up to 190 liters of water each day. Normally, a mature oyster can clean between 11 and 45 liters 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. They close their shells to rest, even when they are 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. Oysters are important for both nature and people, giving us food. However, they face problems like diseases and changes in their environment.

As an 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 bigger. The shape of an oyster depends on where it first attaches. Oysters usually become adults in one year. In their first year, they release sperm into the water. Later, they release eggs. In places like bays, oysters usually release their eggs and sperm from late June to mid-August. 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.

The largest area for oyster production in the United States is the Chesapeake Bay, though there are fewer oysters there now. 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 Europe, France leads in oyster farming.

Oysters are eaten by crabs, seabirds, starfish, and humans.

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 helps make the water clearer and better.

In places like Maryland, people have used oysters to help clean the water. One acre of oysters can clean a lot of water each day. This helps the environment and can also create jobs and bring money to local communities.

Ecosystem services

Oysters are important for nature. They help keep water clean by filtering it and support many plants and animals. Oyster reefs protect shorelines from big waves and storms. When oysters grow together, they make homes for many sea creatures. Because of these benefits, people are working to protect and restore oyster reefs.

Human history

Oysters have been an important food for humans for thousands of years. People in the past left behind piles of oyster shells, called middens, showing they ate oysters long ago. In 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 liked to eat oysters with beer, especially a type called oyster stout. Brewers found that adding crushed oyster shells to beer helped make it clearer. This started in 1938 in London.

Oysters used to be cheap and eaten mostly by working people. In the 19th century, New York City had huge oyster beds. Millions of oysters were sold each day, and they helped start the city’s restaurant business. But over time, many of these oyster beds were destroyed, and today oysters cost more and are seen as 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. But 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 stop 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. But 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 eaten oysters for a very long time. We know this because we find many oyster shells in places all over the world. Oysters are popular food near coastlines, and some places even have festivals to celebrate them.

There used to be a belief that oysters were only safe to eat in months that have the letter “r” in them. This was because in warmer months, oysters can spoil more easily.

Oysters can be eaten in many ways. They can be served on the half shell, raw, smoked, boiled, baked, fried, or in many other ways. Sometimes they are used in dishes like Oysters Rockefeller. When eating them raw, people often add butter, salt, or lemon juice. Some restaurants serve them with a special mix called mignonette sauce. Oysters taste different depending on where they come from.

Oysters are good for you because they have important nutrients like zinc, iron, calcium, selenium, vitamin A, and vitamin B₁₂. They are also low in calories.

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

Diseases

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

One disease is called "Dermo." It is caused by a tiny creature called Perkinsus marinus. It can make many oysters die and affect 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 moved up the east coast of the United States.

Another disease is called MSX. It 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 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.