The lower intertidal zone is mostly submerged underwater most of the time and is only exposed when it is low tide.  The lower intertidal is more rich in organisms, more so than the middle intertidal zone.  There is more species richness in the lower intertidal because the organisms are submerged in water most of the time, so more interaction takes place.  As was mentioned, the species richness is high, a listing of the organisms can be found here, [Organisms].