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



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


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.

Fun Facts About Giant Kelp

1. Giant kelp grow to 100 feet (30 m) on average but can reach lengths of 175 feet (53 m) in ideal conditions.

2. Giant kelp grow at an average rate of 11 inches (28 cm) a day but can grow 24 inches (61 cm) a day in ideal conditions.

3. Decomposing kelp that sinks to the seafloor provides food for animals in the deep sea.

4. Sea otters wrap themselves in giant kelp to keep from floating away while sleeping.

5. Giant kelp grows faster than bamboo.1

6. Giant kelp hold onto rocky substrates using their “anchors” (or holdfasts) at the bottom of the kelp.

7. Giant kelp are not plants, but rather extremely large brown algae.2

Engage Youth with Sailors for the Sea

Oceana joined forces with Sailors for the Sea, an ocean conservation organization dedicated to educating and engaging the world’s boating community. Sailors for the Sea developed the KELP (Kids Environmental Lesson Plans) program to create the next generation of ocean stewards. Click here or below to download hands-on marine science activities for kids.

Kids Environmental Lesson Plans


1 Monterey Bay Aquarium

2 NOAA Sanctuaries