安定同位体と消化管珪藻分析による干潟植物網の解析について

現生生態学と古生態学の接点

抄録

The tidal flat at the mouth of the Obitsu River is one of the best areas for ecological research around Tokyo Bay. Annual variation in the biomass, collected 1 m grid units, showed that the seagrass Zostera japonica which grows at the middle intertidal zone along the river route, has a great influence on the ecosystem. During the summer it forms zostera beds, providing a good habitat for fauna, while during the winter most of the grass disappears except for the roots. The benthonic diatom fractions also increase during the summer. Analysis of the gut contents showed that Batillaria cumingii contained Cocconeis scutellum, a benthonic diatom which lives on Zostera japonica, while the gastropod Umbonium moniliferum and the bivalves Tapes japonica, Mactra veneriformis, Mactra chinensis, Dosinia Japonica and Solen strictus, on the sandy bottom of the lower tidal zone, contained a wider composition of benthonic diatoms. Stable carbon isotopic analysis showed that the primary producers in the Obitsu River tidal flat consisted of benthonic diatoms (-19 to-16‰), seagrasses (-11 to -14‰) and salt marsh plants (-26.5 to -24.5‰). ¹³C ratios for the Batillaria cumingii from the zostera beds were about 1.5‰ higher than for benthonic diatom fractions from the same location. ¹³C ratios for the other primary or higher consumers are between the ratios of the benthonic diatom fractions and the zostera, suggesting that they have a mixed diet.