Giant kelp

Animal Facts

  • Scientific Name

    Macrocystis pyrifera

  • Animal Type

    Plants & algae

  • Diet

    photosynthesis converts the energy of light to the energy of carbohydrate molecules

  • Size

    in general to 100 feet (30 m); 175 feet (53 m) possible in ideal conditions

  • Relatives

    sea palms, bull kelp; family: Lessoniaceae

  • Habitat

    Kelp Forest

  • Range

    along the coast from Santa Cruz to Turtle Bay, Mexico and along the temperate coasts of South America, New Zealand, and Australia

Natural History

This majestic giant of the kelp forest grows faster than tropical bamboo—about three to five inches each day in our exhibit and 10 to 12 inches in the bay. Under ideal conditions, giant kelp can grow an astonishing two feet each day.

Held upright by gas-filled bladders at the base of leaflike blades, kelp fronds grow straight up to the surface, where they spread across the top of the water to form a dense canopy. Giant kelp often grows in turbulent water, which brings renewed supplies of nutrients, allowing the plants to grow to a possible height of 175 feet. The stemlike stipes are tough but flexible, allowing the kelp to sway in ocean currents. Unlike a proper root system, the holdfast—a coneshaped mass of branching extensions called haptera—doesn't carry nutrients or water; it anchors the kelp to a rock.


During a population surge, sea urchins—which normally eat pieces of kelp that fall to the seafloor—will feed on the stipes of giant kelp plants and can completely destroy a kelp bed. Otters, voracious eaters, have helped preserve kelp forests by feeding on urchins.

Kelp is harvested for use in aquaculture. Studies seem to show little, if any, negative affects from harvesting. Kelp could be seen as a renewable resource.

Sludge, silt or sewage dumped near kelp forests can cover and destroy the microscopic stage of giant kelp.

Cool Facts

Giant kelp is harvested as a source of algin, an emulsifying and binding agent used in the production of many foods and cosmetics, like ice cream, toothpaste and cereals.

Pieces of decomposing kelp (detritus) sink to the depths of the ocean, providing food for deep sea creatures.

Giant kelp has a multitude of inhabitants. Invertebrates graze on the blades, fish seek shelter in the fronds and thousands of invertebrates live in the holdfast—such as brittle stars, sea stars, anemones, sponges and tunicates. Sea otters like to hang out in the kelp forest, where they find their favorite food and can wrap up in a kelp frond to keep from drifting away at naptime.

As kelp grows, a blade at the tip of each frond separates, producing a series of tiny new blades. The logo of the Monterey Bay Aquarium represents the tip of a growing kelp plant.

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