[B-BG21_1PO1] 熱帯ー亜熱帯沿岸生態系における物質循環

[BBG21-P03] 二枚貝の炭素・窒素安定同位体比による養殖域からの懸濁物拡散の評価

*森本 直子¹、梅澤 有²、田中 義幸³、レジーノ ジュネビエーブ⁴、渡邉 敦⁵、マックグローン マリア・ローデス⁴、宮島 利宏¹ (1.東京大学 大気海洋研究所、2.長崎大学 水産学部、3.海洋研究開発機構 むつ研究所、4.フィリピン大学 海洋科学研究所、5.東京工業大学大学院 情報理工学研究科)

キーワード：懸濁物食二枚貝, 海草, 養殖, 炭素・窒素安定同位体比

Recently there is growing concern about the impact of densely-deployed aquacultures on coastal marine ecosystems in the Philippines. As suspension-feeding bivalves are expected to reflect local food sources, their effectiveness as an environmental indicator were examined by analyzing stable carbon and nitrogen isotope ratios of bivalves living in aquaculture and neighboring seagrass areas. As a whole, the δ¹³C and δ¹⁵N of bivalves collected in the seagrass areas ranged from -13.1 to -11.0 and from +4.0 to +6.6, respectively, but in seagrass area where water mass from aquaculture area passed through typically lower values (-18.9 ~ -16.1 and +2.7 ~ +5.2, respectively) were observed, and they were the lowest in the aquaculture area (-24.4 ~ -19.8 and +3.4 ~ +4.3, respectively). It suggests that bivalves mainly fed on sinking particles, and presumably also seagrass-derived particles in seagrass areas. Higher C/N ratio was observed at sites where impact of aquaculture was larger. Although the interspecies differences and food selectivity etc. may affect the variability of the bivalve δ¹³C and δ¹⁵N to some extent, these results demonstrated that stable isotope ratios of bivalves could be used as an effective indicator to evaluate propagation areas and actual effects of suspended matter resulting from anthropogenic source on ecosystems.