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Kelp forest facts for kids

Kids Encyclopedia Facts
Diver in kelp forest
A diver in a kelp forest off the coast of California

Kelp forests are a type of marine ecosystem that is present around colonies of kelp; they contain rich biodiversity. Kelp can stretch up to 200 feet (60 meters) from their anchors on the sea floor to the surface.

They provide home to many fish and invertebrate species. Kelp forests also often attract mammalian visitors, including whales, sea lions, sea otters, and SCUBA-diving humans.

Kelp forests draw their name from an analogy to forests on land.

They occur worldwide throughout temperate and polar coastal oceans. In 2007, kelp forests were also discovered in tropical waters near Ecuador.

Kelp forests can influence coastal oceanographic patterns and provide many ecosystem services.

However, the influence of humans has often contributed to kelp forest degradation.

Environmental Characteristics

Kelp forest-blue
Kelp Forest

Kelp forests are found in temperate ocean waters around the globe wherever water conditions are conducive to the successful establishment of kelp colonies. Kelp favors clear waters between about 4 and 20 degrees Celsius; various species of kelp favor different ranges of temperatures, but none grow in waters where the temperature is consistently warm.

Kelp forests are typically found in waters between 1 and 24 meters below the low tide mark; the tops are often partially exposed on very low spring tides, with the tops of the kelp sticking 20 to 30 cm out of the water. Water clarity is a key factor determining the depth of water a kelp forest can thrive in, as sufficient light must reach the depth where kelp are anchored to the sea floor and first start to grow.

A high nutrient content, moderate water movement via wave action or current, and a hard base for attachment are also all necessary requirements for the establishment of a kelp forest.

Major kelp forests can be found in both the Northern and Southern hemispheres, along the coasts of western Europe, northeast Asia, western North America (from southern California to Alaska), South Africa, southern Australia, and the west coast of South America.


This section details the characteristics of kelp as it affects the kelp forest as an ecosystem. For more information on the organisms classified as kelp, see kelp.


Mother sea otter with rare twin baby pups (9137174915)
The sea otter is an important predator of sea urchins. Sea urchins damage the kelp forests by chewing on them

The general morphology of various kelp species form the basis around which the kelp forest ecosystem is built. Kelp plants have three basic structural units:

  • The holdfast is a root-like tangle, which fixes a kelp to the sea floor or other anchoring surface.
  • The stipe is a long slender stalk, which extends vertically from the holdfast toward the surface.
  • The fronds are leaf-like attachments to the stipe, are very numerous, and are the major sites of photosynthetic activity.

In addition, many kelps have pneumatocysts, or air bladders, located along the stipe or at the base of fronds, to help the kelp maintain a roughly vertical posture.

Kelp usually grows to the surface, and may continue to grow in length after reaching the surface, causing a canopy of floating fronds to develop. This dense vertical infrastructure with overlying canopy forms a system of microenvironments similar to those observed in a terrestrial forest, with a sunny canopy region, a partially shaded middle, and darkened floor. Each of these regions provides different niches for many types of animals and other plants.

Growth cycle

Rockfish around kelp Monterey Bay Aquarium
Rockfish swimming around giant kelp

Kelp grows extraordinarily quickly. In ideal conditions, Giant kelp can grow 30-60 centimeters vertically per day. Therefore, kelp forests rapidly reach a "mature" status, in striking contrast to terrestrial forests, which may take hundreds of years to mature.

Some kelp species live for only one year (analogous to annual terrestrial plants), while others live for up to seven years (corresponding to perennial plants). In perennial kelp forests, it is common to see the highest growth rates during the spring and summer months, with a corresponding dieback during the winter. Winter storms can also affect the growth cycle of kelp by tearing holes in the canopy, pruning fronds from kelp, or even dislodging entire kelp plants from the sea floor. This helps sunlight filter down to lower depths and creates gaps where new kelp plants can establish themselves.

Kelp forest
Kelp Forest

Inhabitants and visitors

Vertebrate aquatic animals

Harbor Seals, Sea Otters, Sea lions, Sea Bass, Swell shark, Angel shark, Horn shark

Human use

Calliostoma annulatum
The jeweled top snail grazing on a blade of giant kelp

Kelp forests have been important to human existence for thousands of years.

Modern economies are based on fisheries of kelp-associated species such as lobster and rock-fish. Humans can also harvest kelp directly to feed aquaculture species such as abalone and to extract the compound alginic acid, which is used in products like toothpaste and antacids. Kelp forests are valued for recreational activities such as SCUBA diving and kayaking.

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