As the waves roll in, the sea level around the crab's island will rise. Each wave clears the previous shells, and deposits a new shells. After the waves crash, the sea level begins to decrease around the island. The lower water level is good for collecting the best shells that were previously out of reach. Listen carefully to the ocean waves, as they indicate when the sea level will rise. Be sure to have time to return to the island with your prize shells before the next wave! Watch the sun and the moon in the night sky, as they are clues to the sea's behavior.