Meaghan Weeden | June  08, 2020 | 4 min read

What is a Kelp Forest

Kelp (order Laminariales) are large brown seaweeds, with 30 different genera. that live in cool waters close to the shore. While kelp is similar to a plant, they are not a plant, as they lack tissues to carry water and food from one part to another.

In order to grow, kelp will attach to the seafloor and will grow to the water surface, relying on sunlight to generate food and energy. This is why kelp is coastal species and needs shallow, clear water to survive.
While kelp isn’t technically a tree, kelp growths are called “kelp forests” because they form dense groupings, tower above the ocean floor, and perform many of the same functions that traditional forests do. And they’re no less important — or threatened — than their terrestrial counterparts.

They provide nutrition and homes for biodiversity just like terrestrial forests.

Where are kelp forests found

Kelp forests are found in rocky shorelines, mainly on the Pacific coast, from Alaska to Baja, California. Kelp forests grow further from the tropics than seagrass beds, coral reefs and mangrove forests, meaning that kelp forests do not overlap with those ecosystems. However, similarly to the above ecosystems, though, kelp forests are very important for biodiversity, as they provide an underwater habitat to hundreds or thousands of marine species of fish, invertebrates and other algae.

kelp forest shallow water

How Does Kelp Grow?

Reliant on light for photosynthesis, kelp grow along rocky coastlines at depths ranging from 6 to 90+ ft. Tiered like a terrestrial forest with a canopy and several layers below, kelp forests do best in cold, nutrient-rich upwellings (areas where the ocean layers overturn, bringing cool, nutritious bottom waters to the surface). And similar to trees, they have root-like “anchors” called holdfasts that keep them from floating away. But unlike trees, their “roots” don’t burrow deep under the surface, but rather grip tightly onto the ocean floor.

Kept afloat by pneumatocysts (gas bladders), kelp grow rapidly toward the ocean's surface — and when we say rapidly, we mean it! Although their typical growth rate is around 10 inches a day, giant kelp can grow up to 2 ft in ideal conditions. Bull kelp, another common variety, grows 4 inches a day — which is still pretty impressive if you ask us!

A perennial, Giant Kelp can live for up to 7 years if it isn’t uprooted by a storm or devoured by hungry sea-dwelling herbivores. Bull kelp, an annual, goes through its entire life cycle in just 1 year, but both have a two-stage growth trajectory.

In the beginning, they exist as spores, released by the millions by their parent kelp, sporophytes. These spores then grow into tiny male or female gametophytes, which can produce either sperm or eggs. After fertilization occurs, these free-floating embryos quickly grip the ocean floor and develop into mature plants.

Seal swimming in kelp

Source: Smithsonian Photographed by Kyle McBurnie

why are kelp forests important

Kelp forests are important because they form a dense barrier between coastlines and damaging waves, providing food and shelterto thousands of marine animal species, as well as other algae.

Similar to coral reefs, mangrove forests, and warm-water seagrass beds, kelp forests provide an important underwater habitat, being home to many different animal species, as well as other algae species, including fish, shellfish, sea urchins, snails and sea otters.  

Larger marine mammals like sea lions, harbor seals, and sea otters use kelp forests for feeding and protection from predators. Connected to water and sky, sea birds like gulls, terns, snowy egrets, great blue herons, and cormorants also benefit. And on rare occasions, even grey whales have been spotted seeking refuge from predatory killer whales. 

 Some animal species use kelp forests as spawning grounds, and while other marine animals use kelp as a place to stay to raise their young in the relative safety. We say relative, because sharks and other marine mammals hunt in the long corridors that form between rows of individual algae.

coral reef

Source: UC Santa Barbara

why human activity is a threat to kelp forests

Knowing that kelp can grow up to 2 ft per day, you might think they’re virtually invincible. But unfortunately, that isn’t the case for this incredible underground ecosystem. In fact, from Tasmania and Australia to Norway, western Europe, and the west coast of North America, kelp forests are under dire threat. And while warming ocean waters are taking a toll (and will continue to do so if climate changecontinues unchecked), the biggest threat comes from sea urchins. Sea urchins love kelp and will eat through an entire kelp forest in no time. 

Unfortunately, when the last kelp strand has been cut down, large herds of sea urchins respond to the stress of starvation by becoming aggressive and growing larger, more powerful teeth. These new teeth allow them to crunch through just about anything in their path, which only compounds their destructive influence. And once things have progressed to this point, there’s virtually no chance of kelp coming back.

Today, the NPS oversees 419 parks and monuments spanning over 84 million acres of land across the U.S. and has inspired similar organizations in countries around the world. It is, arguably, one of our greatest American institutions!

A remarkable phenomenon of marine ecology, "urchin barrens" occur when their populations grow to such extraordinary densities that vegetation on the entire seafloor is annihilated, leaving behind an ecological wasteland. And as they gather and multiply, a virtually impenetrable barrier is formed, which prevents anything else from coming back. Unfortunately, once established urchin barrens will persist indefinitely. 


kelp forest conservation

While there is little hope for kelp forests that have already been annihilated and turned into urchin barrens — or for those that grow in rapidly warming waters — scientists have been investigating and experimenting with different ways to help for some time. And what they’ve discovered is that sea otters are to kelp forests what wolves are to Yellowstone.

Because as it turns out, sea otters love urchins just as much as urchins love kelp! And if left alone, they will happily keep the urchins in check. But when they decline, urchin populations explode. For this reason, sea otters are considered a keystone species (similar to the stone at the top of an arch that prevents the other stones from falling down, keystone species prevent the collapse of entire ecosystems) in kelp forests. Another species that loves to dine on sea urchins? Rock lobsters.

There you have it — everything you didn’t know you needed to learn about kelp forests! The next time you visit the coast, keep your eyes peeled — if you’re lucky, you might just spot their characteristic tendrils swaying slowly with the tides.

Looking to learn more? Discover the different types of forests from around the world. 

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Plant Trees Where They're Needed Most

As the need for reforestation is global and ever-changing, we feature where trees are most needed now. Today, we're raising funds to jumpstart forest fire recovery in British Columbia. Learn more

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  • This reforestation initiative is helping to restore the landscape in British Columbia after the Hanceville fire burned over 590,000 acres in 2017 and natural regeneration has not occurred. The fire has impacted the forest, soils, riparian ecosystems, wildlife, and water quality. Local indigenous communities have seen their ability to hunt and gather food drastically altered. But your support will go a long way! The goal of planting trees here is to not only re-establish a healthy forest, but also to plant species that will be resilient in the face of climate change. Thank you so much for your support of healthy forests! 🌲
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