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European flat oyster
Common name:European flat oyster
Scientific name:Ostrea edulis
Alternative common names:
Common oyster, edible oyster, eetbare oester (Dutch), Essbare euster (German), and European oyster.
Ostrea edulis is a species of oyster. It is a sessile, filter-feeding bivalve mollusc, associated with highly productive estuarine and shallows coastal water habitats. Each valve differs in shape and size; the left one (the one used by the oyster to attach itself to a surface) is concave, while the right one is flat and fits snugly inside the left.
Where does this species come from?Europe
What is its invasive status in South Africa?NEMBA category 3.
Where in South Africa is it a problem?Western Cape.
How does it spread?They have been intentionally transported around the globe in order to establish or enhance aquaculture ventures. They have been imported into South Africa since 1894.
Why is it a problem?They are well known to act as vectors of marine alien species. These may include the introduced aquaculture species themselves, epi- or infaunal organisms associated with them, disease micro-organisms and multicellular parasites.
What does it look like?Description: European flat oyster is a bivalve mollusc that has an oval or pear shaped shell with a rough, scaly surface. The irregular shell has a distinct hooked beak, patterned with delicate foliation. The two halves (valves) of the shell are different shapes sub circular to circular and inequivalve. Left shell is deeply concave and fixed to the substratum, the right being flat with rougher edges and sitting inside the left acting as a lid. Inner surfaces of both valves are smooth and usually pearly, white or bluish-grey, often with darker blue areas. Valves are held together at their narrow ends by an elastic ligament. No teeth are reported on the hinge. A large central muscle serves to close the valve against the pull of the ligament. The shell is off white, yellowish or cream in colour with light brown or bluish concentric bands on the right valve. Shell consists of a series of chalky layers which may include laminar and hollow chambers. The hard rough grey shell contains a meat that can vary in color from creamy beige to pale grey, in flavour from salty to bland, and in texture from tender to firm. Habitat: They prefer the firm bottoms of mud, rocks, muddy sand, muddy gravel with shells, hard silt, and artificial habitat created with broken shells. They can be found in muddy areas attached to hard surfaces at depths of 9.144 metres. Breeding: European flat oyster is a protandric hermaphrodite, changing sexes generally twice during a single season. Females are fertilized by externally released sperm. It produces between 500 000 and 1 million eggs per spawning. Following an incubation period of 8-10 days, depending on temperature, final release into environment occurs.