An Estimation of Fish Biomass and Attached Organisms beneath Oyster Rafts in Hiroshima Bay, Japan

Hiroshima Bays is top production approximately 60% of oyster production in Japan. For cultivate of oyster, fishermen use hanging rafts. A thousand of raft is hanging during 2-3 years in the bay. Large-scale oyster culture may change the ecosystem structure and material cycles in the bay through the filtration of particulate matter by oysters and other associated animals. This study described the community structure of marine organisme in terms of fishes surrounding and animal attached on oyster rafts. Field observation was carried out from 2016 to 2019 at oyster farming in Hiroshima Bay. Oyster production and provisioning for the fish habitat were also evaluated by placing underwater video cameras beneath oyster culture rafts. The result showed that black seabream was high biomass and oyster it shelf was bigger bioyster for animal attached on oyster raft. The number of individual, mussel is most abundance of animal attach on oyster raft with ratio 9:1 than number of oyster. Maintaining oyster culture is important not only for maintaining oyster production, but also for maintaining fish production by enhancing material cycles through the paths in the food chains of Hiroshima Bay under oligotrophic conditions.