Oyster
The largest oyster-producing body of water in the United States is Chesapeake Bay, although these beds have decreased in number due to overfishing and pollution. Willapa Bay in Washington produces more oysters than any other estuary in the US. Other large oyster farming areas in the US include the bays and estuaries along the coast of the Gulf of Mexico from Apalachicola, Florida in the east to Galveston, Texas in the west. Large beds of edible oysters are also found in Japan and Australia. In 2005, China accounted for 80% of the global oyster harvest. Within Europe, France remained the industry leader.
Didemnum vexillum
The Portuguese oyster ("Crassostrea angulata") cultivated off the Atlantic coast of France and Portugal was largely killed by an iridoviral disease in 1969. To replace the stock, large quantities of Pacific oyster ("Crassostrea gigas") spat were imported from Japan. Some efforts were made to kill any fouling organisms that might be associated with the spat by immersing it for two periods, each of one hour, in fresh water. However, in the early 1970s, there were reports of a brown "Didemnum " ascidian on oyster beds in the region. Around the same time, oyster spat from Japan was introduced into the Pacific coastal regions of Canada and the USA and soon afterwards an ascidian was observed there, and later identified as "D. vexillum". By 2014, this tunicate was present in the eastern Atlantic, North Sea and Mediterranean Sea in the Netherlands, the United Kingdom, Ireland, France and Italy. On the east coast of North America its range extended from New Jersey, New York, Connecticut, Rhode Island, Massachusetts and New Hampshire, to Maine. In the eastern Pacific its range extends from Alaska to California. It is also present in New Zealand, where it was first observed in 2001, its only known encroachment into the Southern Hemisphere.