Competitors and fouling organisms in the hanging culture ofthe Pacific oyster, Crassostreagigas (Thundberg)

Generally speaking the “enemies”; of oysters can be divided ecologically into three classes: 1) “parasites”; which live within the body of the oyster and cause harm, 2) “competitors (fouling organisms)”; which occupy the same ecological niche as the oyster and cause harm indirectly by, contesting the available food and living space, 3) “predators”; which feed on the oyster. The sort of harm which can affect oysters differs widely with cultivation technique and habitat conditions. For instance, with the raft hanging method, long line method and other intensive cultivation practices which involve submersion in the sea, the harm from competitors such as Mytilus edulis gcdloprovincialis, tunicates and barnacles is most noticeable. On the other hand, with natural reproduction and sowing methods or the rack hanging method, in which the cultivation generally takes place in the littoral zone or on sea bottom, the most prevalent harm is caused by such bottom dwelling predators as drills (murices, naticids), sea stars, and so on. Of course, damage caused by parasites can be seen equally on all of the above.