If you are not familiar with the ocean, you may be surprised to find a small bay filled with water later transformed into a large stretch of beach with extensive tide pools.  This daily cycling of the water level is caused by tides.  Tides are created by a combination of the effects of the moon and sun's gravitational forces.  Gravity from the moon and sun pulls the water away from the earth's surface enough to create the tides.  The moon has the greatest effect because it is much closer than the sun, which acts to reinforce the moon's gravitational pull when the moon is between the earth and sun in a new moon.     When the earth is between the sun and the moon, the sun pulls water from one side of the earth while the moon pulls from the other side.  In between these times, tides are not as extreme.  Oregon and most of the Pacific coast have two uneven high tides and two uneven low tides, the highs usually followed by the lowest.  The average of the lower tides is designated as the "0" from which the heights are measured.  http://web.mit.edu/corrina/tpool/tides.html

Spray Zone
    The range of this zone is from about 7.5' (2.5 meters) to 10' (3.3 meters.) The Spray zone is just reached by the ocean's salty spray. Only the highest tides and winter storm waves flood this area. Periwinkles live on the higher rocks of this zone, rarely splashed by the ocean. Limpets dwell on the lower end of this zone. Barnacles can also live here.

High Tide Zone
    Exposed to waves during high tides, the high tide zone gets enough water to provide a home to a greater variety of ocean life than the spray zone Only organisms that can survive rough waves and long exposure to air can survive here. Because barnacles glue themselves to the rocks and close when the tide is out, they are well adapted to this zone. Rockweed, sea lettuce, and other algae cover the rocks, providing protection from the sun for many organisms that live here. When the tide goes out, seawater is often trapped in the rocks, forming permanent tide pools. Hermit crabs are frequent visitors in tide pools.

Mid zone
    The mid tide zone is covered and uncovered twice a day by tides. Animals in this zone have gotten used to being covered in air and sea water. Anemones close up when the tide is out, keeping in the moisture necessary for survival. Mussels close their shells tightly for the same purpose, and open to feed as the tide brings in their food. Snails Limpets and other animals dwell in this zone. Many types of sea weeds grow here also.

Low Tide
     Usually covered by water, the low-tide zone is exposed to the air only when there are very low tides . Because of the longer submersion period, organisms here do not have to be strong and adaptive. This is why more organisms make this zone their home. A variety of seaweed grow here, providing shelter for many small animals such as crabs, shrimp, and small fish. Purple Sea Urchins find plentiful food in this zone and thrive here. The animals of this zone are often preyed upon by animals of the sub-tide zone.

Sub-tide zone
    The sub tide zone is hard to access because it is rarely exposed to the air. The organisms here are more fragile and cannot tolerate too much exposure to the air or sun. When this area is made available, it can be very exciting to find some of these rarely seen animals.