5. Dynamical Properties of Coastal Currents in the Northwestern Part of Iriomote Island Part. 2—Funauki and Shirahama Bays

This chapter presents investigation of the physical properties of tidal flows in two semi-closed bays connected with a channel based on theoretical, observational and numerical frameworks. Shirahama Bay with shallower water and Funauki Bay with deeper water in the northwestern part of Iriomote Island are mutually connected by a channel. Tidal flows in both bays are expected to be much more complex than those of Sakiyama and Amitori bays, discussed in Chap. 4. According to the tidal flow dynamics in Chap. 4, the seawater exchange in Shirahama Bay is more active because of its shallower water floor, whereas the seawater exchange in Funauki Bay is more stagnant because of its deeper water floor. Consequently, the low-salinity water originating from a river is likely to be retarded in Funauki Bay under near-calm conditions. In the case of a smaller aspect ratio (shallower and longer) of the connecting channel, the seawater exchange among the bays becomes inactive. In the case of the moderate aspect ratio of the connecting channel, which is comparable with those of both bays, the seawater exchange among the bays reaches a maximum. For a larger aspect ratio (deeper or shorter) of the connecting channel, the seawater exchange will stagnate not only between the bays, but also between the bays and the open ocean. The aspect ratio of the connecting channel, which strongly affects the tidal currents in both bays, is expected to strongly influence on the dispersions of eggs and seeds in the coastal ocean ecosystems in this region.