The great kelp is a species of brown alga (Algales, Marronacea) found in the Great Kelp Ring.
Like most kelp, it is a massive alga. Particularly, it may reach 450 metres in height. They create similarly massive canopies that often cover the sea in a permanent shade. Such organisms have long lifespans of many decades.
In order to float, like other brown algae, it has many cysts along its stipe. They are filled with air and buoy.
Its younglings are able to survive in the shade thanks to both the cold waters in the depths and to the fact that their spores are encased in large, nutrient-rich hardy seeds that resemble coconuts. The vastness of their parents allow them to produce dozens of these at a time.