Science & Nature • Marine biology

Kelp

Kelp are large brown algae, not plants, that grow in cool, nutrient-rich coastal waters.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

Kelp are large brown algae, not plants, that grow in cool, nutrient-rich coastal waters. They form dense underwater forests that are among the most productive marine ecosystems, providing food, shelter, and habitat structure for many coastal species. Along Canada’s Pacific coast, especially in British Columbia, kelp forests are important for fisheries, marine biodiversity, and coastal ecosystem health.

Biology

Kelp are large brown seaweeds rather than true plants. Their body plan typically includes a holdfast for anchoring to rocky seafloors, a stipe for support, and blades for photosynthesis. Many species also have gas-filled bladders called pneumatocysts that keep the blades near the surface, where light is abundant.

Habitat and distribution

Kelp grow in cool, nutrient-rich coastal waters, especially on rocky substrates. They are most common in temperate and polar regions, often in shallow, clear water. Worldwide, they are found along temperate coasts and in other cold marine areas.

Kelp forests

Dense kelp growth forms underwater forests that create complex habitat structure. These forests support high biodiversity, including many fish, invertebrates, and other marine animals, and are considered highly productive coastal ecosystems.

Human uses and importance

Kelp has long been harvested for industrial uses, such as production of potash and iodine. Today it is also studied for its ecological role, carbon storage potential, and importance in coastal food webs.

Key facts

Kelp are marine algae in the brown algae group, commonly placed in the order Laminariales.
They anchor to rocky seafloors with holdfasts and grow upward with stipes and blades.
Many kelp species use pneumatocysts to keep blades near the surface.
Kelp forests support high biodiversity and are major coastal ecosystems.
Kelp forests are important along Canada’s Pacific coast, especially in British Columbia.

🍁

Canadian context

Kelp forests are important along Canada’s Pacific coast, especially in British Columbia, where they support fisheries, marine biodiversity, and coastal ecosystem health.

Frequently asked questions

What is kelp?

Kelp are large brown algae that live in marine environments, especially cool coastal waters. They are not plants.

What is a kelp forest?

A kelp forest is an underwater ecosystem formed by dense kelp growth. It provides habitat, food, and shelter for many marine organisms.

Where does kelp grow?

Kelp grows mainly in cool, nutrient-rich coastal waters on rocky seafloors, especially in temperate and polar regions.

How many kelp species are there?

Sources describe roughly 30 species worldwide, though taxonomic treatments can vary.

Why is kelp ecologically important?

Kelp are primary producers and ecosystem engineers that support biodiversity, coastal food webs, and habitat complexity.

References

NOAA Office of National Marine Sanctuaries — https://sanctuaries.noaa.gov/visit/ecosystems/kelpdesc.html
Supports: Kelp are large brown algae, not plants; their structure, habitat, and role in kelp forests.
Encyclopaedia Britannica — https://www.britannica.com/science/kelp
Supports: Definition of kelp as brown algae, approximate diversity, habitat, and historical uses.
Smithsonian Ocean Portal — https://ocean.si.edu/kelp-and-kelp-forests
Supports: Distribution, depth and temperature range, ecological role, and carbon storage.
World Resources Institute — https://www.wri.org/insights/what-kelp-forests-protect
Supports: Kelp as a subgroup of brown seaweed, not plants, and the ecological structure of kelp forests.
Coastal Wiki — https://www.coastalwiki.org/wiki/Kelp_forests
Supports: Kelp forests as productive marine ecosystems formed by large brown macroalgae of Laminariales.