there are 2000 species of brown algae. most species live in the ocean. they are important as food and as homes for many animals and marine life. some brown algae are gathered by humans for food. the giant kelp "macrocystis" is a brown alga that forms underwater forests, and it may grow to 60 meters. the sargasso sea gets its name from the "sargassum" seaweed that floats on the surface. many brown algae grow on rocks at the seashore.