Assessing Ecosystem Services of Oyster Culture in Hiroshima Bay; Result of Prey-predator Numerical Model

Hiroshima Bay is famous with its oyster culture, supplying ca. 60% of total oyster production in Japan. The farmers are applying three different modes for oyster culture; Ikisu, Yokusei, and Nokoshi. These different modes for oyster culture make the oyster harvest period longer and stable harvest amount in successive amount. The present study focuses on evaluating the ecosystems services provided by oyster culture. We carried out field observations at three oyster raft stations from June to August 2016 to identify and quantify attached animals. Identification and quantification of fish gathered under oyster rafts were also made by video recordings. To understand the role of oyster culture in nutrient cycle of the bay, we constructed 26 compartments of the numerical model. We observed three bivalve species and three filter feeder animals attached on the cultured oysters. Eleven fish species were recorded under the oyster culture rafts, and a half of them were commercially valuable species. Based on the model outputs and using the nitrogen trading market, we estimated that ecosystem value provided by nitrogen removed from the system was $1,696 year^-1 and $1,082 year^-1 through the denitrification and oyster harvest rate, respectively. This value excludes the commercial oyster harvest in the dockside market. It is concluded that oyster culture significantly contributes to ecosystem service as water quality improvement and habitat provisioning for fish and other animals