Once upon a time, there was a little red crab who lived in a large rock pool on the edge of the ocean. He shared this beautiful rock pool with his parents and many other interesting sea creatures.
As the high tide came in and out every day, it filled the pool with fresh sea water, flushing out the old water.
From time to time new sea creatures would get washed into the pool along with the high tide. This kept life in the rock pool quite interesting—you never knew who or what you may meet the next time you looked.