The Olympia Oyster - Coastal Interpretive Center

Introduction

Oysters are a crucial species of marine animal that help to stabilize sediment, provide habitat for other marine creatures, and improve water quality (1). Without oysters, many healthy estuaries, bays, mudflats, and eelgrass beds would be in poor condition. Countless plants and animals would be worse off as a result. Therefore, it is essential that abundant, healthy, and sustainable populations of oysters survive in the wild to help our waterways be the best they can be. There is only one species of oyster that is native to the west coast of North America and that species is the Olympia Oyster (Ostrea lurida).

Physical Characteristics and Habitat

The Olympia Oyster is a sedentary, bivalve mollusk. Both of its valves are about the same size. The upper (right) valve is largely flat, and fits into the concave lower (left) half of the shell (1). Like most bivalves, Olympia Oysters don’t have wings near the hinge. They also don’t have regularly spaced radial ribs (1). However, they do have small chomata (folds located on the inside of the shell near the hinge ends) like other Ostreidae species (1).

The Olympia Oyster’s shell is thinner than the shells of most oysters. It does not contain periostracum, a coating on the outermost shell of many shelled animals that helps to keep the underlying shell from eroding (1). As a result, the Olympia Oyster’s shell may erode over time, making their already thin shell even smaller.

Olympia Oysters live in estuaries and bays, as well as areas surrounded by mudflats and eelgrass beds (1). They prefer to make their homes in bodies of water that are up to 233 feet (71 meters) deep (1). They also prefer to live reasonably warm bodies of water, with their ideal water temperatures being between 43- and 68-degrees Fahrenheit (6 to 20 degrees Celsius) (1).

Olympia Oysters make their homes on solid substrates. Olympia Oysters attach themselves to the substrate of their choosing by cementing their left valve to it (1). To do this, they secrete a glue-like material from their byssus gland (7). The valve then conforms to the shape of the substrate (1).

Olympia Oysters have rounded shells that can sport a variety of colors. They are typically either white or a purplish shade of black. However, some shells also sport brown or yellow stripes (1). The oyster’s flesh varies in color from white to a light olive green (1).

Olympia Oysters are small creatures. They are typically only 2.4 to 3.1 inches long (6 to 8 centimeters), and 1.6 to 2.4 inches wide (4 to 6 centimeters) (1).

Reproduction

Olympia Oysters are hermaphrodites, meaning they have both male and female reproductive organs. Their annual spawning period takes place between May and August, which is typically when the water reaches approximately 57.2 degrees Fahrenheit (14 degrees Celsius) (1).

When an Olympia Oyster spawns for the first time, it acts as a male, releasing sperm from its mantle cavities (1). The sperm is released in the form of a sperm ball, which dissolves into free-floating sperm in the water (1).

When an Olympia Oyster spawns again, it will act as either a male or female (1). It will continue switching between the sexes for subsequent spawning periods (1). Spawning periods can occur once or twice per year, depending on the temperature of the water (2).

When it acts as a female, the Olympia Oyster’s mantle cavity serves as a brooding chamber, which is where the eggs will be fertilized by the free-floating sperm (1). Once the eggs are fertilized, they move into the branchial chamber (1). The branchial chamber is the space that is located between the Oyster’s gills (4). The eggs then develop into veliger larvae and begin to develop an eye spot and a foot. Once these are developed, they will migrate to find a hard surface to attach to (1). An average brood of Olympia Oyster larvae ranges between 250,000 and 300,000 Oysters (2).

The maximum lifespan of an Olympia Oyster is currently unknown. However, it is believed that it is longer than a decade (1).

Diet

Olympia Oysters have a very limited diet, consisting solely of phytoplankton (1). Phytoplankton are microscopic plant-like organisms that can be found in bodies of water (8).

Climate Concerns

The Olympia Oyster is slower to adapt to changing climate conditions, such as the acidification of the ocean, the warming of the ocean, and the destruction of habitat (1), thus putting the long-term survival of the species at risk.

The acidification of the ocean is of particular concern because water that is more acidic limits a young Oyster’s ability to a form a shell, thus making it more vulnerable to predators (1), such as birds, rays, and rock crabs (2), and less likely to survive long enough to reproduce.

The warming of the ocean is also of particular concern because water temperatures may become too warm during the Olympia Oyster’s traditional late spring/early to mid-summer spawning season, thus inhibiting the species’ ability to reproduce regularly. It can be reasonably assumed that the right water temperatures will continue to exist. However, they may come at different times of the year. Whether or not Olympia Oysters will be able to adapt to changes in when the warmer water temperatures they need for spawning occur remains to be seen.

Habitat restoration efforts are currently underway in Puget Sound, Netarts Bay (Tillamook County, Oregon), and San Francisco Bay to try and help the species have a fighting chance against these threats. The efforts have been successful, so far (1).

Washington State’s Efforts to Conserve the Olympia Oyster

Here in Washington State, Olympia Oysters have been a State Candidate species since 1997. State Candidate species are those that may be reviewed by the Washington Department of Fish and Wildlife (WDFW) for listing as sensitive, threatened, or endangered in the future (3). The Olympia Oyster is also included on WDFW’s list of Priority Habitats and Species (PHS), which is a catalog of habitats and species that are considered high priorities for conservation and management (3).

Recreational harvest on public tidelands of Olympia Oysters is currently banned under WAC 220-56-310, which prohibits the recreational harvest of any oyster with a shell size of less than 2.5 inches (3). Annual Bivalve Management Plans in place between the Washington State Government and Puget Sound Treaty Tribes protect Olympia Oysters on public tidelands that have a shell size of less than 2.5 inches from being harvested commercially by the Treaty Tribes (3). That being said, Olympia Oysters may be harvested by the Treaty Tribes for ceremonial and subsistence purposes (3).

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