What is the Black Stuff Inside Oyster Shells?

Oysters are filter feeders, taking in everything from microorganisms and algae blooms to debris such as sand. Their shells also store items that don’t quite qualify as real waste but instead make up pseudofaeces (the latter known as pseudofaeces).

Pea crabs are an unavoidable part of oysters, and many raw bar shuckers consider eating them normal. Unfortunately, however, these little guys can be difficult to open without breaking your jaw.

Mud worms

Black blisters slithering across oyster shells make for an unappetizing appetizer, but these unseemly spots have deeper significance than simply looking gross. They’re actually signs of Polydora websteri worm burrows created in response to polypectomy; worms that have been responsible for the collapse of oyster populations in Australia and South Africa and are suspected of creating similar damage at Washington state oyster farms.

Worms feed off of detritus that accumulates on oyster surfaces before breaching inner valves with their excrement, eventually filling any open space with detritus, mud and worm feces–resulting in what’s known as a “mud blister.” Worms don’t harm humans but pose a nuisance for oyster farmers who must pay to clean off these blemishes from their products before shipping.

Researchers have observed that heavy mudworm infestations can cause oysters to grow more slowly, thus decreasing their market value and making them more vulnerable to predation. Worms also reduce shell strength in their hosts making them more prone to being eaten by predators.

People used to believe that live marine worms living inside oyster shells was a sure sign of freshness; these worms, however, are actually the result of poor serving practices and not from within the oysters themselves. A recent post which went viral on Facebook–but has since been removed–criticized a restaurant for serving oysters with mudworms instead. That post was misleadingly based on inaccurate press releases issued from Louisiana State University Sea Grant College Program and provided false information.

Pacific oysters are our primary aquacultural source, while Olympia oysters play an integral part of Puget Sound’s ecological, cultural, and economic health. Numerous organizations such as the Department of Fish and Wildlife and Puget Sound Restoration Fund are making significant strides toward re-establishing Olympia oyster populations; however, their efforts could be compromised by mysterious shell-boring pests causing disease outbreaks; researchers are working hard to gain a better understanding of these pests in order to create effective ways of controlling them.


Phytoplankton are microscopic algae that convert solar radiation to energy while fixing carbon dioxide from the atmosphere, acting as the foundation of every ocean food web and producing nearly half of Earth’s oxygen supply. Furthermore, phytoplankton are an integral component of global carbon cycling as a major source of organic carbon.

As opposed to land plants, phytoplankton lack roots and stems but instead form long chains of cells covered by tiny hairs for water absorption. Since they rely solely on sunlight as energy source, phytoplankton are known as obligate photoautotrophs; meaning they cannot obtain energy from any source other than sunlight itself. They are found everywhere from freshwater bodies like lakes to saltwater bodies like oceans; living at the surface layer known as the euphotic zone where sunlight levels are at their highest, to deep waters where nutrients come upwelled through deep waters containing deep waters upwelled from deep waters; experiencing population explosions called blooms due to seasonal changes and changing conditions – even hypersaline basins contain phytoplanktiophytes have blooms due to unpredictable seasons and conditions!

Dinoflagellates and diatoms are two of the main classes of phytoplankton. Dinoflagellates use flagella, or whip-like tails, to propel themselves through water currents; typically green or red in hue and possessing complex shells made of silica. Diatoms do not possess flagella but instead possess hard, layered structures called frutubums which serve as storage organs to store their food such as other algae, bacteria, and detritus particles.

Oysters rely heavily on phytoplankton as food and filter the water they drink by filtering out debris from it. Furthermore, phytoplankton are essential components of our global food chain as they make up most aquatic vegetation and supply nutrition to animals–including humans!

Once a phytoplankton cell dies, bacteria begin to digest it to release nitrogen gas and other forms of organic carbon back into the water – known as “microbial loop.” This process serves to regulate how carbon moves between ocean and atmosphere.

Oysters’ ability to fix nitrogen, an essential mineral found in all living things, demonstrates their microbial loop. Fixing nitrogen into water bodies helps balance out acidity levels which threaten marine life. As such, oysters play an essential part of ecosystem but overusing can cause disease and toxic algal blooms that pose risks to people and wildlife if too much fertilizer runsoff into these water bodies. It is thus vital that an appropriate limit be set on runoff into bodies of water bodies from fertilizer applications.


Some may dislike oysters because of their texture and lack of taste; others love them raw, baked, or charbroiled – although just like other raw food items they can contain harmful bacteria such as E coli, Listeria Salmonella, Vibrio or other threats that pose potential threats.

Vibrio bacteria is notorious for causing food poisoning, known as vibriosis. They typically thrive in warm and brackish water environments and enter human bodies through eating contaminated seafood or through wounds exposed to saltwater. According to the Centers for Disease Control and Prevention (CDC), each year, this strain of Vibrio bacteria results in hundreds of illnesses as well as deaths.

Oysters collect bacteria by filtering contaminants out of their surroundings as they feed. Cooked shellfish does not pose any threat, while raw oysters may remain harmful until harvested and consumed; according to the Centers for Disease Control (CDC), undercooked oysters can pose a real danger for people with compromised immune systems or existing conditions such as liver or kidney disease or diabetes.

Bacteria aren’t the only organisms living inside an oyster; in addition to tasty algae and fungus varieties, its bivalves contain various microorganisms that help make up its environment – algae fungi protozoa are among them – helping maintain cleanliness as well as digestion of its food sources.

These organisms, beyond providing nutrients to oysters, also contribute to their unique flavors and contribute to pearl production as they create materials used to form shells of oysters.

Bacteria are essential parts of an oyster’s digestive system and help give the shellfish its slimy texture and distinctive smell.

As for the other black stuff found in oysters, this could actually be their waste–at least part of it. When an oyster feeds, its waste accumulates inside its shell in an accumulation cavity and includes both real feces as well as pseudofaeces–such as sand or larger bits of food it cannot digest.

Pseudofaeces may not be dangerous, but they do smell bad. Luckily, oyster mucus and nacre can cover these irritants to create pearls – concentric layers of nacre compose each pearl!


Oysters play an essential role in maintaining ecosystem health as they filter excess nutrients out of water sources. Excess nutrients can cause eutrophication, leading to an increase in algae growth that, when decayed, releases carbon dioxide and consume oxygen from the atmosphere – an effect which oysters help counterbalance by filtering away these extra nutrients while simultaneously providing additional oxygen into their ecosystems.

Polydora websteri Hartman, a spionid polychaete found in southern Puget Sound intertidal waters, has recently caused a spate of shell-boring mud blisters on Pacific oysters (Crassostrea gigas Thunberg). These burrows can be unpleasant to consumers and, if punctured during shucking, may leak mud and detritus into oyster meat. In addition to oysters, this infestation also includes mussels, scallops and abalone species – adding even further commercial value to these valuable commercial species.

Some have mistakenly thought the black substance inside oysters is feces; instead it’s made up of mineral-rich waste material produced by oysters through secreting thick liquid called chitin that dissolves elements present in water to form an adhesive substance that forms hard shells.

An oyster’s shell must expand in order for it to grow larger, and this is accomplished by secreting a thick gelatinous substance which pushes outward the sides of its valves. Chitin may also be used to strengthen and harden its surface surface of its shell surface.

Starting its lifecycle, an oyster’s life cycle begins when its fertilized egg hatches into a free-swimming larva that develops within 24 hours into a crawling larva, using its foot to move across surfaces in water and finally finding an area to settle, whereupon it secretes cement-like substances to bond to substrate surfaces.

Oysters are protandric, meaning they can change from male to female as environmental cues indicate it is time. Temperature of water, food availability, and other conditions all can play a part in whether an oyster is ready to spawn. When fertilized this way, fertilized oysters produce oocysts (encased eggs) of Cryptosporidium parvum parasite found worldwide and known to cause diarrhea, cramps, and nausea symptoms in humans.