The giant kelp is one of the largest kelp found in the ocean.  They are also known and referred to as seaweeds.  They tend to grow in offshore colder waters to 60 ft. in depth.  The bigger kelp forests of Southern California are located off Santa Barbara and Point Loma.  These kelps can grow from the subsrates that it's attched to up to and beyond 100 feet.  There may be smaller plants that grow in the upper intertidal zones, but they most likely will not survive.  It's been said that the giant kelp can grow up to a whole foot in one day.  Many times after storms they are found washed up onto the beaches.  These forests are, in my opinion, even more interesting than the land forests.  If a land forest was to have it's top four feet chopped off, it would most likely take years to recover.  If you were to take the same method and apply it to the giant kelp, it would grow back in a few weeks to a few months.  That's pretty amazing, if you ask me.