The force of gravity pulls inward toward Earth's center of mass and holds water on our planet's surface. This is easily seen in the image above and at left. A Brief Explanation of the Basic Astronomical Factors Which Produce Tides and Tidal Currents.
Tide pools are small pools maintained by water brought in and flushed out by tides.
A wide range of life forms can be found in tidal pool communities. The location of an organism relative to the tide level significantly affects the physical conditions it faces. So, tide pool residents must be able to cope with a highly variable environment. Organisms that live near the top of the high tide line are submersed in water only occasionally. Organisms that live near the low tide line are almost always under water.