Numerical analysis of convective dispersion of pen shell Atrina pectinata larvae to support seabed restoration and resource recovery in the Ariake Sea, Japan

In this study, numerical simulation of convective dispersion of the larvae of the pen shell Atrina pectinata was conducted to support effective seabed restoration in the Ariake Sea, Japan. A two-dimensional depth-averaged model consisting of a continuity equation and Navier-Stokes momentum equations was developed to reproduce tidal currents in the Ariake Sea. This larval transport model was then used to predict migration of larvae drifting on tidal currents. To determine effective areas for seabed restoration, 14 release points were defined in the model as potential new spawning grounds for the pen shell. The number of larvae that migrated from these points to habitable areas for pen shells (depth: 2 < h < 20 m, grain size median diameter: >62.5 μm) was calculated for each release point. Because of the anticlockwise tidal residual flow in the inner bay of the Ariake Sea, pen shell larvae also had anticlockwise trajectories. Larvae originating from the northeast area spread out over a large area, while larvae originating from the northwest area reached only the western area. Most of the larvae originating from Isahaya Bay flowed out through the mouth of the Ariake Sea. Consequently, larvae released from the northeast area (particularly from Point 13, Noku 210) reached the largest habitable area. In addition, most of the larvae ultimately drifted to Isahaya Bay, suggesting that seabed restoration in the northeast area and Isahaya Bay would be the most effective approach to recovery of pen shell resources.