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Species Database

Nereocystis luetkeana - Bull Kelp

Bull Kelp image

Geographic range:

Aleutian Islands, Alaska to San Luis Obispo County, California

Key features:

Single, very long stipe and a bulbous pneumatocyst.


bay (rocky shore), exposed rocky shore, kelp forest, protected rocky shore

Primary common name:

Bull Kelp

Synonymous name(s):

Fucus luetkeanus

General grouping:

Brown seaweed/algae

ITIS code:


Geographic Range

Range Description:

Nereocystis luetkeana ranges from the Eastern Aleutian Islands, Alaska, to San Luis Obispo County, California.

Intertidal Height

Lowest intertidal height:

0 meters OR -2 feet

Highest intertidal height:

0 meters OR -2 feet

Intertidal height notes:

Nereocystis luetkeana is extrememly rare in the intertidal.

Subtidal Depth Range

Minimum depth:

0 meters OR 0 feet

Maximum depth:

17 meters OR 56.61 feet

Subtidal depth notes:

Nereocystis luetkeana grows from the subtidal to 17 meters in depth and is abundant on subtidal rocks.


bay (rocky shore), exposed rocky shore, kelp forest, protected rocky shore

Habitat notes:

Nereocystis luetkeana grows in exposed, turbulent areas, often at the edges of giant kelp beds. It forms dense kelp beds on subtidal rocks and can be found as deep as 17 meters. They form large kelp forests that provide important sheltering habitat for young fish and invertebrates, including urchins, sea stars, snails and crabs. These forests also provide habitat for sea otters since sea otters eat the invertebrates that live on the kelp forest floor and the kelp itself provides a canopy which the otter can anchor to while resting to keep from drifting away.


Relative abundance:


Species Description

General description:

Nereocystis luetkeana is a brown algae in the family Lessoniaceae. It is famous for forming large kelp beds which can be seen as a large brown canopy at the surface. It is an opportunist and rapidly colonizes areas that have been cleared by urchins. Nereocystis luetkeana attaches itself to various rocky substrates by a massive, root-like holdfast. A stipe arises from the holdfast, extending to the surface, being held afloat by a gas filled float that contains oxygen (from the plantís photosynthesis), and nitrogen, but also up to 10 percent carbon monoxide by volume. This annual seaweed dies off in winter and can be found washed up onto beaches where the plants dry and turn brown. Nereocystis luetkeana has the appearance of a bull whip, giving this kelp its common name.

Distinctive features:

Nereocystis luetkeana is a large brown kelp that attaches itself to rocks with a holdfast made of many finger like projections, collectively referred to as haptera. The holdfast can be up to 10 cm in diameter and supports a single, narrow, cylindrical and whip-like stipe that can be 10-20 m tall and 1 cm in diameter at its base. As it grows towards the surface, the stipe gradually increases in diameter, becomes hollow and terminates in a pneumatocyst that can be up to 15 cm in diameter. From the float, two clusters of long narrow blades grow from the float. Each cluster may contain up to 64 blades which are up to 10 m long and 15 cm wide.


Nereocystis luetkeana can grow to 35 m.

Natural History

General natural history:

Nereocystis luetkeana is an annual seaweed, which means it grows from a spore to a mature plant in just one year. It grows rapidly in the summer, sometimes as much as 25 cm per day, and faster during daylight hours than at night. As Nereocystis luetkeana approaches the surface, its growth slows and more energy is diverted towards spore formation. The blades of Nereocystis luetkeana form by splitting along predetermined weakened lines. They grow out continuously fomr a meristem located at their base and slough off at their older outer tips. The detritus formed by the sloughing tips has recently been shown to be an important source of carbon for inshore intertidal communities. This detritus feeds many of the filter feeders, such as Pacific Blue Mussels,Mytilus trossulus in the intertidal zone.

Blades shape can vary in Nereocystis luetkeana according to environment. Some Nereocystis luetkeana have narrower and flatter blades than others. There narrow, flat blades tend to collapse into streamlined bundle that enable these individuals to live in areas of stronger current. Whereas individuals with wider, more ruffled blades would be torn from the rocks by strong currents. However, ruffled blades tend to remain more spread out, which decreases self-shading, which is an advantage in areas with a low current. Thus it appears that blade shape is a trade off between streamlining in areas with a heavy current and avoiding self shading. Another way that Nereocystis luetkeana is designed to deal with drag from stressful water conditions is that the fibrils of cellulose in the walls of stipe cells are oriented mostly at a 60 degree angle to the long axis of the stipe. This allows the stipe to stretch, especially near the base, when it is in turbulent water conditions.


Urchins feed on Nereocystis luetkeana. Blue rockfish, Sebastes mystinus, consume many Nereocystis luetkeana sori on their descent to the bottom. This edible kelp is also eaten by humans and harvested to make a variety of commercial products.


Nereocystis luetkeana converts energy from sunlight and nutrients through photosynthesis.

Feeding behavior


June - November


Once Nereocystis luetkeana is mature, usually in the summer or late autumn, it forms spore patches, called sori on the blades. The sori are released usually at dawn or shortly thereafter. Since the sori are released near the sea surface, and begin releasing spores as they descend, they have the potential for wide dispersal. However, they are relatively heavy and usually sink to the ocean floor, where they continue to release spores for several hours. This ensures that spores settle close to parent plants and on suitable substrate.

When the spore forming organs settle, they release their spores, which can germinate and develop into microscopic gametophytes. There are probably billions of spores released from every individual kelp. The proximity of gametophytes to each other enhances prospects of fertilization and new saprophyte production. In addition to proximity, reproductive success is enhanced by the powerful pheromone lamoxirene that is released by female gametophytes. Even in small amounts, this pheromone causes an explosive release of sperm from male gametophytes and also acts as a sperm attractant.
Click on an image below to view a larger version in the SIMoN Photo Library. You will also be able to view important information on each photo such as photographer, date, caption and more.
Alden, P., F. Heath, R. Keen, A. Leventer, and W. Zomlefer. 2002. National Audubon Society Field Guide to California. A.A. Knopf, New York, NY.
Langstroth, L. and L. Langstroth. 2000. A Living Bay: The Underwater World of Monterey Bay. University of California Press, Berkeley and Los Angeles, CA. 287 p.
Maier, I. and D.G. Muller. 1986. Sexual pheromones in algae. Biological Bulletin. 170: 145-175.
Mondragon, J. 2003. Seaweeds of the Pacific Coast: common marine algae from Alaska to Baja California. Sea Challengers, Monterey, CA. 97 p.
O'Clair, R.M. 2000. North Pacific Seaweeds. Plant Press, Auke Bay, Alaska. 162 p.
Monterey Bay Aquarium. Online Field Guide, 2008.