Pacific oyster. Close-up of the inside of a Pacific, or Japanese, oyster (Crassostrea gigas). This edible oyster is native to the Pacific coasts of Asia. It has been introduced to other coastal areas worldwide, but is generally considered an invasive species. Oysters are found on coasts in the intertidal zone, where they filter plankton and other particulate matter from the water. They are protected from predators by their hard mineralised shells. The green colour is due to the presence of Haslea ostrearia bacteria.