抄録
Evaluation of carrying capacity of coastal waters is reviewed for sustainable exploitation of biological production from coastal aquaculture. Accurate estimation of phytoplankton primary production and understanding of oxygen dynamics are of prime importance for scaling the carrying capacity. Preliminary results on the carrying capacity of Otsuchi Bay, a ria in Sanriku coast on the northeastern coast of Japan are summarized. Bio-optical sensors for natural and active fluorescence prove to be useful approaches for rapid and accurate quantification of primary production. This was exemplified by field application of both the natural fluorescence technique and the pulse amplitude modulation of fluorescence to monitor primary production in aquaculture ground. Growth of the cultured kelp called wakame, Undaria pinnatifida was compared with that of phytoplankton as competitors for nutrients during spring. As another important factor determining the carrying capacity, oxygen supply of subsurface layers is considered. During summer time, oxygen consumption of bottom sediment under shellfish rafts was high enough to exhaust dissolved oxygen within three to five days. However, no anoxic water was formed. Wind-driven circulation and inflow of subsurface coastal waters induced by the internal tide supplied enough dissolved oxygen to prevent the formation of anoxic layer.
