Naha – At low tide, the sea withdraws from Okinawa’s coast, exposing a landscape suspended between shore and ocean. Shallow pools shimmer in the morning light. Patches of seagrass sway beneath the surface. Across the reef flats, harvesters in wetsuits move slowly through knee-deep water, dragging blue mesh bags behind them and gathering tangled strands of brown seaweed from the seabed.