Why secondary production of boreal brackish water is high?-Clarification over the maintenance mechanism of excellence and over benthic system-

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We carried out field surveys to compare the food demand of the clam based on the secondary production of the clam population to both the amount of the clam in the field and stable isotopic contribution to the diet of the clam of the potential food sources. We discuss how the dense patches and high secondary productively of the clam population are sustained in the ecosystem on tidal flats in the lagoon. The contribution by using only the isotope sign seems to have the risk of somewhat misleading of the contribution. Contribution of the benthic diatom showed relatively wider range based on only stable isotopic data. Subsequently, reasonable contribution of the benthic diatom was estimated up to 68 % based on the phytoplankton biomass and food demand of the clam, and the benthic diatom seemed to be the most important food sources of the clam. In this study, the large amount of the benthic diatom in subtidal area seemed to play a key role of the stock for the food sources of the clam