All About Oysters

Crassostrea gigas or Pacific or Japanese oyster

Crassostrea gigas, Japanese Oyster, or Pacific Oyster 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 to be an invasive species, where it is outcompeting native species, such as the Olympia Oyster, Ostrea conchaphila, in Puget Sound, Washington, the rock oyster, Saccostrea glomerata in the North Island of New Zealand and the blue mussel, Mytilus edulis, in the Wadden Sea.

Crassostrea ariakensis or Suminoe oyster

The Chinese River Oyster is native to Japan, China, India, and Pakistan. In the 1970s a few West Coast hatcheries started raising and marketing them as the new summer oyster; replacing the Pacific Oyster (Crassostrea gigas), which isn’t as palatable during the summer months. At the same time, the Eastern Oyster (C. virginica) was in decline on the East Coast due to overharvest and disease. Virginia aquiculturists started experimenting with sterile river oysters in 1998 with the aim to replace the native with a disease-resistant oyster.

These early experiments showed that the river oyster was both disease-resistant and faster growing. Soon a contentious debate began about whether fertile oysters should be introduced in the Bay. From 2000 to 2002 the Virginia Seafood Council and the Virginia Marine Resources Commission stocked over a million experimental sterile oysters to look at the feasibility of an introduction.

But after years of study and debate, the Army Corps of Engineers and the states of Maryland and Virginia prohibited the introduction of fertile river oysters and ended cultivation of sterile oysters in open waters.

Crassostrea angulata or Portuguese oyster

The Portuguese Oyster or Cupped Oyster, Crassostrea angulata, is a species of oyster found on the coasts of Spain, Portugal, and Andorra. This oyster is closely related to the Pacific Oyster (Crassastea gigas) Although first identified as a native European species, genetic studies have suggested the Portuguese oyster originated from the Pacific coast of Asia and was introduced to Europe by Portuguese trading ships in the 16th century. The species is usually found in coastal river mouths and estuaries.

Prior to nearly being wiped out by a viral disease in 1969, C. angulata was extensively cultivated in France and Portugal as part of the edible oyster industry. The Pacific oyster, which is more resistant to the disease, was introduced in the 1970s and has since replaced C. angulata as the main commercial species in that area. Currently, the Portuguese oyster is not cultured in large numbers commercially.

Crassostrea sikamea or Kumamoto oyster

Kumamoto oysters (Crassastrea sikamea) were classified as a new variety of oyster in 1928: "This variety is common in the shallow, muddy water of Ariake Bay in Saga Prefecture (Japan). It is a dwarf or stunted form, and is devoid of commercial value owing to its small size." Fast forward to today, and the Kumamoto is a hugely popular oyster in the US.

There are varying accounts as to how the Kumamoto ended up on US shoals. The prevailing thread is. Pacific oysters were imported to the US from Japan since 1890. After WWII ended the demand for oysters increased in the US. Late in 1945 Japan was asked to export 80,000 cases of oyster seeds. They did not have enough of the typical Pacific oysters, Cassostrea gigas to fill the order, so they shipped Kumamoto oysters with them. Oops. The first shipment of Kumamoto oyster seed arrived in Seattle, WA in 1946.

Between 1947- 1953, the Washington Department of Fisheries brought in Kumamoto oysters and planted them in Washington, Oregon, and Hawaii. These plantings prompted a number of commercial growers to produce Kumomotos.

By the mid-1980s, purebred Kumamotos nearly impossible to find. In Japan, they were extinct due to pollution. In the Pacific Northwest, the Kumomotos and the Pacific oysters had cross-bred to the point where it was hard to find the smaller Crassastrea sikamea. Genetically pure Kumamotos were found on property owned by Taylor Shellfish Farms, and these were expanded into today’s stock.

Crassostrea virginica or Eastern oyster

The Eastern Oyster, Crassostrea virginica, naturally occurs in the Gulf of the St. Lawrence, Canada, along the Atlantic coast of the United States to the Gulf of Mexico to the Yucatan Peninsula, Mexico and to the West Indies and the coast of Brazil. It is also found in the estuaries of the main Hawaiian Islands where it was introduced in 1866.

Hit by decades of heavy fishing, deadly diseases, and environmental pressures, native oysters in the Chesapeake Bay, Crassotrea virginica, today number less than 1% of levels a century ago. As recently as 1980, the Chesapeake Bay accounted for roughly 50% of the U.S. oyster, but over the past decade, the region has produced only 1-5% of the total domestic supply of oysters. Despite various efforts to restore the oyster population, this decline—and its adverse effects on the oyster industry continues.

Ostrea angasi or Australian flat oyster

The multitude of bays spanning South Australia’s Eyre Peninsula are well known for producing large quantities of Australian Flat Oysters. A hundred years ago, however, the industry looked very different. Local fishermen were taking up to six million native Australian oysters (Ostrea angasi) from wild stock every year.

As the oyster beds receded, so did any chance for young native oyster larvae to take hold and they were nearly wiped out from the region. They were replaced by the Pacific Oyster (Crassostrea gigas), which was then farmed in smaller, sustainable leases. Now, as farmed oysters have come under threat of disease, the native angasi oyster is starting to make a comeback and may eventually dominate the industry in Australia once again.

Ostrea edulis or European flat oyster

The European Flat Oyster Ostrea edulis, a native of Europe, has been part of the human diet for many centuries. The Romans built ponds to stock and sort oysters. In the 17th century, oyster spat were collected on rocks, separated from each other and deployed into ponds in salt marshes on the Atlantic coast of France. A decline in activity in salt marshes facilitated oyster culture development by expanding grow-out acreage availability. During the 18th and 19th centuries, fishing effort led to over-exploitation, failing recruitment, and destruction of European natural beds, which were also affected by extremely cold winters

A massive mortality widely struck European flat oyster populations in 1920. The population later recovered but was replaced by cupped oysters in several traditional rearing areas. Disease spread again in the early 1970s and 1980s, drastically reducing the production of O. edulis in almost all European traditional rearing areas. Despite new management practices, and intensive repletion programs, the production of O. edulis has remained low since that time. Most European Flat Oysters now come from the US, but only the oysters raised in France may carry the name Belon.

Ostreola conchaphila (lurida) or Olympia oyster

For millennia, the native people of Puget Sound relied on the Olympia Oyster as a key part of their food supply. Its abundance in South Puget Sound gave the Squaxin people a valuable asset to share and trade with their neighbors and allies throughout the region.

When American settlers arrived on Puget Sound in the mid-1800s, they also depended on shellfish as a staple food. Very early on, Olympia Oysters became an export product, allowing the development of one of Washington’s most enduring industries.

The numerous shallow bays of South Puget Sound provide ideal habitat for Olympias. In the mild climate, spawning begins in May and continues through August. Despite their small size, Olympia Oysters require several years to reach full maturity and may live as long as fifty years.

Olympia Oysters are sensitive to environmental factors and mainly grow below mean low tide where they are always covered with water. They require clean water to thrive and naturally occurring temperature extremes sometimes damage them.

As the only indigenous West Coast oyster, with a range from Baja California to Alaska, it sustained Native Americans for millennia. Lewis and Clark gorged on them, and Gold Rush forty-niners literally loved them to death, depleting vast beds in the San Francisco Bay and beyond. Even in oyster-rich southern Puget Sound, where pioneers crowed that “when the tide is out, the table is set,” the free meal ended. By the late 1920s, polluted wastewater from pulp mills slowly decimated Olympia stocks.

But Olympias are now on the rebound, thanks largely to the Puget Sound Restoration Fund, a group of growers, state and federal agencies, Native American tribes, tideland owners, and passionate environmentalists who scour beaches for wild Olympias and use them to grow seed oysters, which are then distributed in the sheltered bays and estuaries that are the Olympia’s historical habitat. And as self-sustaining, naturally spawning populations have been reintroduced, farmed production—though still less than 1 percent of Washington’s oyster output—has held steady.

Saccostrea glomerata (commercialis) or Sydney rock oyster

The Sydney rock oyster, Saccostrea glomerata, formerly known as Saccostrea commercialis, is an oyster species endemic to Australia and New Zealand. In Australia it is found in bays, inlets and sheltered estuaries from Wingan Inlet in eastern Victoria, along the east coast of New South Wales and up to Hervey Bay Queensland., around northern Australia and down the west coast to Shark Bay in Western Australia.

There is also a small introduced population on Flinders Island, in Bass Strait, Tasmania and in Albany on the south west coast of Western Australia, where they are farmed. In New Zealand, where the species is not farmed, it is known as the New Zealand rock oyster.

The Sydney rock oyster is closely related to Saccostrea cucullata, or hooded oyster, which is common on Indo-Pacific rocky shores. Sydney rock oysters are capable of tolerating a wide range of salinities (halotolerant).

Tiostrea chilensis (lutaria) or New Zealand flat oyster

Variously known in New Zealand as Bluff oyster, dredge oyster and flat oyster, or by its M?ori name “tio.” This much-loved delicacy is really the Chilean oyster – Ostrea chilensis.

Found all around the New Zealand coast in small patches to depths of 35 meters or more, dredge oysters grow in extensive beds in the South Island’s Foveaux Strait, Golden Bay and Tasman Bay.

In New Zealand, they are a prized delicacy, and harvested from March to August from the Foveaux Strait oyster fishery, which centers on the town of Bluff (hence the local name). From the early 1980s, the fishery went into serious decline, due to the outbreak of an oyster parasite, Bonamia exitiosa, with the disease killing an estimated billion oysters between 2000 and 2003. The population has been recovering since 2003, with fishermen voluntarily limiting the catch to half the allowable to aid the revival.