-History

How old do you suppose our shorelines are?  They are of age, but the shorelines are constantly changing.  The most immediate mode of change that we can think of is the crashing of the waves.  Wave action is one of the many ways of changing the shorelines but that is only the microscopic view.  The macroscopic view would be the changes brought on the last major ice age, which occurred 120,000 years ago and lasted about 100,000.  The ice masses, which were 2 kilometers thick, covered about 30 percent of Northern America.  "These ice sheets lowered the global sea lever 120 meters, exposed the coastal margins of North America, and scoured northern latitudes down to bare rock (Bertness, 5)."  The ice covering and scouring of the ice sheets caused major problems in our shorelines.  One can suggest that due to the ice sheets organisms were not able to thrive, and due to the scouring of the ice sheets, extinction would have occurred, or there would have been limitation of organismal growth.

            The last major ice age occurred 120,000 years ago but our shorelines have only been growing for 20,000.  Over that period of time, "temperatures have increased, the ice sheets have retreated, and the sea level has risen (Bertness)."  So, as you can tell, the Northern American shorelines are young and have just begun to thrive in species richness.

            Currently, there are many species of organisms that occupy the North Atlantic shorelines but compared to the inland, where organisms have been thriving for generations, there is no competition.  The changes brought on by the glaciers and time has lowered the number of species in the intertidal zone. "Ice Age events over the past 3 million years decimated the fauna and flora of the western Atlantic and appear to have caused more species extinctions and displacements there than on many other coastlines (e.g., the eastern pacific or the Atlantic; see Vermeij 1991).  Even though the Ice Aged occurred, the intertinal zones are now filled with a wide variety of organisms.

  -The Intertidal Zone

     The intertidal zone is located between the high tide and the low tide on the shores.  The intertidal zone has a vertical zonation pattern.  Intertidal organisms convey zonation in relation to moving farther up the intertidal, and therefore, into more exposed environments.  The intertidal zone is separated into three major zones: the upper intertidal, the middle intertidal and the low intertidal.  Organisms vary from each zone.  It is observable that the upper limit is usually determined by physical factors (temp, dessication, modes of transportation, etc) while the lower limit is usually determined by biological factors.  Due to the different zonation patterns, it can harbor different types of organisms.  The following pages will now explain the differences in between each of the intertidal zones.