炭素・窒素安定同位体比分布から推察した安芸灘に生息する底生動物群集の炭素供給源

抄録

Carbon and nitrogen stable isotope distributions of benthic community in Aki Nada, Seto Inland Sea, Japan were examined, in order to speculate on the importance of the primary benthic production in the areal shallow water ecosystem. A small red sea bream Pagrus major showed the most depleted δ¹³C value (-17.7%0) among the animals. This value was similar to the δ¹³C value of -20.1±1.7%0 reported for pelagic particulate organic matter in the western Seto Inland Sea, indicating that its food source was derived from production in the water column. On the other hand, 94% of the 69 fish (13 species) and all the 25 benthic invertebrates (six species) showed more enriched δ¹³C signatures of -16.0 to -13.4%0. This δ¹³C distribution was unlike the δ¹³C values reported for pelagic particulate organic matter or zooplankton, while being closer to the values of macroalgae, seagrasses, epilithic microphytobenthos and small benthic crustaceans. This suggests that ¹³C-enriched primary benthic producers play an important role in the benthic carbon flow in the areal ecosystem. The relationship between δ¹³C and habitat depth at the three sampling stations was not clear in either benthic animals or macroalgae in the zone of 9-43m in depth. Thus no striking depth-related local differences were found in the δ¹³C distribution of the benthic community in the shallow waters (36m in average depth) of Aki Nada.