In some temperate marine habitats large species of brown algae can be extremely abundant. These ecosystems are known as kelp forests. Because they are extremely productive ecosystems, and have a great deal of physical structure associated with their seaweed biomass, kelp forests provide habitat for a wide range of marine organisms. These include a diversity of species of smaller algae, invertebrates, fish, marine mammals, and birds. The kelp forests of the Pacific coast of North America are estimated to support more than 1,000 species of marine plants and animals.
Kelp forests occur in many parts of the world, including the Atlantic and Pacific coasts of North America. However, the tallest, best-developed kelp forests are in waters 20-210 ft (6-70 m) deep over rocky bottoms off the coast of California. This ecosystem is dominated by the giant kelp (Macrocystis pyrifera), which ranges from central California to Baja California (the genus also occurs on the west coast of South America, and off South Africa, southern Australia, and New Zealand). This enormous seaweed is also known as the giant bladder kelp because of the flotation structures attached to its fronds. The giant kelp begins its life as a microscopic spore, but can grow as immensely long as 200 ft (60 m) and live for 4-7 years. Most of its photosynthetic activity occurs in the upper part of its tall canopy, because the lower areas are intensely shaded and do not receive much sunlight.
Other, somewhat smaller species of Macrocystis occur more widely along the Pacific coast, as far north as southern Alaska. Other giant seaweeds of kelp forests of the Pacific coast include the bull kelp (Nereocystis leutkeana), the elk horn kelp (Pelagophycus porra), the feather boa kelp (Egregia menziesii), and the Fucalean alga (Cystoseira osmundacea).