Studies carried out in various localities of the Province of Concepción, Chile (36º40'S; 70º06'W) estabilished the existence of two principal patterns of zonation defined by the populations of Mastocarpus sp. (¿ ?), Tridaea laminarioides, Gelidium pussflum, Ulva lactuca and Perumytilus purpuratus which occupy the lower hydrolittoral. In submerged levels the populations of Gracilaria and Macrocystis. form growths of moderate dimensions and in shallow waters, Iridaea ciliata, Gymnogongrus furcellatus and Gigartina chamissoii in scatterd patches.