Tides
The alternate rising and falling of the sea levels caused by combined effects of the gravity forces by the moon and the sun and the rotation of the earth. Similar motions occur on large lakes, in the atmosphere and even within the solid earth.
During the tide cycle the sea level rises or floods until it reaches it's highest normal point called high tide. When sea levels drops or ebbs to it's lowest point at low tide. The difference is the tidal range. When the gravity pull of the sun and the moon and by the rotation of the earth tug water into two big bulges. One bulges is located on the edge of the planet close to the moon and same with the other side. Also since the sun is far the moon exerts more than twice as much tidal force on the ocean so that a tidal bulge can form under and follows the moon. When the sun and the moon align the gravity combine to produce the high and low tides called Spring Tides. When the moon and sun are perpendicular they pull the sea in different directions and moderate tides called Neap Tides.
The timing, size, and speed of tide make different shape of the coastline seafloor topography, river discharge, and even wind and weather conditions. The zone of the intertidal zone it is also know as the foreshore and seashore. It is an area that the water is above at low tide and underwater at high tide. It has different habitat for different animals like stars fish, sea urchins. It has four subdivision- the spray zone and the upper, middle, and lower intertidal zone. The spray zone is wet and break waves but is submerged it support very limited life. The high zone is underwater but only during high tide. The middle zone if mostly tide. And the low zone is only exposed to air during the lowest spring tides.
To survive they need to be avoid drying out endure temperatures extremes, have intense sunlight, and survive a wide range of salinities. What some organism do to protect themselves is for example anemones sticks together to reduce their surface area. Snails and clams gets closer to conserve moisture and repel predators. Mobile animals goes under the sand or rocks. Sea stars have thick skin and strong skeleton that can handle wave energy. Also sea slugs and other snails have large feet that grabs tightly to surface as they move or rest. Some of the challenges on coastal areas have is because the tides they can be expensive and dangerous also can cause storms and tsunami.