Giant Kelp | Oceana

Corals and Other Invertebrates

Giant Kelp

Macrocystis pyrifera


Temperate Eastern Pacific Ocean and Temperate Waters of All Oceans in the Southern Hemisphere



Feeding Habits


Conservation Status



Class Phaeophyceae (Brown Algae), Family Laminariaceae (Kelps and Relatives)


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Reaching heights of more than 100 feet (30 m), the giant kelp is the largest “seaweed” and the largest of all marine algae. It lives in cold, clear waters where it forms large, dense kelp forests that provide habitat for thousands of other marine species. Though it resembles a tall grass, giant kelp is not a plant. Instead, it is a brown alga and is part of the large kingdom of life known as the Protista. Most protists are single-celled organisms, but the giant kelp is a complex species and is the largest protist in the world.

Since the giant kelp is not a plant, it does not have roots.  Instead, it obtains all of the necessary nutrients directly from the water and is attached to the rocky bottom by a structure known as a holdfast.  Like plants, however, the giant kelp harvests the sun’s energy through photosynthesis and does not feed on other organisms.  This species is one of the fastest growing species in the world, and under perfect conditions, it has been known to grow up to two feet (60 cm) in a single day.  Once and individual giant kelp reaches the sea surface, it continues to grow horizontally, floating in large mats that shade the water column and sea floor below.  In order to remain upright, each giant kelp blade (leaf) includes a gas-filled pod that floats.  Several individuals growing together can create dense forests that are an important ecosystem in temperate, coastal areas where they live.  Several species eat Giant Kelp, and fluctuating populations of Purple Sea Urchins are known to play a role in kelp forest formation and destruction.  Several species of sharks, bony fishes, lobsters, squids, and other invertebrates are known to live in or near kelp forests.

Humans use giant kelp for food and use chemicals derived from this species as components in several other products.  It is rarely harvested from natural forests, however, and is instead often grown in aquaculture operations.  Its fast growth rate and natural means of generating energy (from the sun) make it an ideal species to grow in these sea farms.


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