Underwater towers of algae: why kelp forests are the ocean's most productive neighborhoods

Nature · Published 3 October 2026 Swipe more like this →

In short: Kelp forests are not plants, yet they grow like terrestrial forests, reaching toward the sun in cool, nutrient-rich coastal waters. These dynamic ecosystems support a staggering diversity of life, from microscopic invertebrates to marine mammals, while buffering coastlines against wave energy and storing carbon in the deep ocean.

Kelp are large brown algae, not plants, belonging to the order Laminariales. They anchor themselves to rocky seafloors using root-like structures called holdfasts. From these bases, flexible stems known as stipes reach upward, supporting leaf-like blades that capture sunlight for photosynthesis. Many species utilize gas-filled bladders, or pneumatocysts, to maintain buoyancy, allowing the blades to float near the surface and form a dense canopy. In ideal conditions, giant kelp can grow as much as 18 inches—or up to 60 centimeters—per day, making them some of the fastest-growing organisms on Earth.

These forests function as layered, three-dimensional neighborhoods. The surface canopy provides shelter for seabirds and resting sea otters, while the midwater zone serves as a corridor for fish like rockfish and garibaldi. At the seafloor, the holdfasts create a foundation for crabs, sea stars, and snails. This structure is essential for biodiversity; kelp forests harbor a greater variety of species than almost any other ocean community. Beyond their biological role, they provide critical ecosystem services, including nutrient cycling, carbon storage, and the mitigation of coastal wave energy.

However, these ecosystems are fragile. They require specific conditions, including hard substrates and cool, nutrient-rich water, and are rarely found deeper than 131 feet. They face severe threats from warming waters, pollution, and overgrazing. When predators like sea otters or sea stars decline, sea urchin populations can surge, stripping away the kelp and leaving behind barren rocky landscapes. Because kelp responds rapidly to environmental shifts, scientists monitor these forests as a primary indicator of overall ocean health, using them to track the impacts of climate change and human activity.

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