Kelp forests grow along cool, nutrient-rich coastlines in a broad band roughly between 40° and 60° latitude in both the Northern and Southern Hemispheres. They thrive in every ocean except the warmest tropical waters, hugging rocky shorelines from Alaska to southern Australia, and scientists have even documented them in unexpected deep-water tropical zones. Their distribution is shaped by a few non-negotiable requirements: cold water, sufficient light, hard substrate to anchor to, and a steady supply of nutrients.
The Global Pattern
Kelp forests are fundamentally a cool-water phenomenon. At high latitudes, limited sunlight restricts their growth. At low latitudes, warm temperatures and competition from other seaweeds keep them out. The sweet spot falls across the mid-latitudes of both hemispheres, where cold currents and coastal upwelling deliver the nutrients kelp needs to grow.
This means kelp forests line much of the Pacific and Atlantic coasts of North America, stretch across northern Europe, wrap around the southern tip of Africa, and span the entire southern coastline of Australia. They’re also found around New Zealand, southern South America, and many sub-Antarctic islands. In total, kelp forests are present on every continent except Antarctica itself, though they grow close to it.
North Pacific: The Largest Kelp Forests on Earth
The Pacific coast of North America supports the world’s most famous kelp ecosystems. Giant kelp, the species most people picture when they think of underwater forests, grows from central Baja California in Mexico up through California and into scattered pockets along the Pacific Northwest. These forests can tower over 30 meters from the seafloor to the surface, creating dense canopies visible from above.
Bull kelp occupies the cooler waters further north, ranging from Point Conception in Santa Barbara County, California, all the way up to Unalaska Island in Alaska’s Aleutian chain. Bull kelp is a single-stalked species that regrows from scratch each year, unlike giant kelp, which can persist across seasons. Together, these two species dominate the eastern Pacific, with bull kelp taking over in the colder, more wave-exposed waters where giant kelp can’t survive.
North Atlantic and Northern Europe
The northwest Atlantic coast of Canada marks a major transition zone for kelp. Subarctic and boreal species overlap here, creating shifting assemblages as conditions change with latitude. Kelp forests extend along the rocky coasts of Atlantic Canada, New England, and down into the northeastern United States, though they thin out as waters warm toward the mid-Atlantic states.
On the European side, kelp forests are widespread along the coasts of Norway, the British Isles, Iceland, and France. Norway’s coastline, with its cold, clear fjords, supports some of the most extensive kelp beds in the Atlantic. These forests are built by different species than their Pacific counterparts, typically broad-bladed varieties adapted to strong currents and seasonal swings in daylight.
Southern Hemisphere Hotspots
Giant kelp reappears in the Southern Hemisphere along the coasts of Chile and Argentina, around the Falkland Islands, and across many sub-Antarctic islands. The cold Humboldt Current running up the Chilean coast creates conditions that mirror California’s kelp-friendly waters, supporting forests across a latitudinal range of nearly 2,500 kilometers.
South Africa hosts four native kelp species along its western coast, where the cold, nutrient-rich Benguela upwelling system pushes productive water to the surface. Sea bamboo and split fan kelp dominate this region, forming dense forests in water that stays cool year-round despite the country’s otherwise warm climate. A smaller species appears sporadically along the southern and eastern coasts, where conditions are less ideal.
Australia’s kelp forests are enormous in scale but surprisingly underappreciated. The Great Southern Reef stretches over 8,000 kilometers of coastline across five states, from the subtropical waters of northern New South Wales down around Tasmania and up to Kalbarri in Western Australia. Covering roughly 71,000 square kilometers, it is one of the largest kelp-dominated ecosystems on the planet. Despite its size, it receives far less public attention than tropical reefs like the Great Barrier Reef. New Zealand also supports significant kelp forests along its cooler southern and western coastlines.
How Deep Kelp Forests Grow
Most kelp forests grow in water shallower than 30 to 40 meters, because they need sunlight to photosynthesize. In areas with heavy plankton blooms or sediment runoff, light fades quickly and kelp can’t take root much below 15 or 20 meters. But in exceptionally clear water, kelp pushes much deeper.
Off the coast of Greenland, in the Disko Bay region near 67 to 70°N latitude, researchers have documented kelp growing deeper than 61 meters. The median depth limit there is about 38 meters, but the clearest offshore waters allow enough light to penetrate for kelp to survive well beyond typical limits. Kelp generally needs at least 1% of surface light to reach the seafloor, and in Disko Bay, that threshold extends down to roughly 67 meters during summer.
Kelp in the Tropics
For decades, scientists assumed kelp was strictly a temperate and polar phenomenon. That changed when researchers predicted, and then confirmed, extensive kelp forests in deep water between the Tropics of Cancer and Capricorn. Using deep-water diving, they documented kelp in eight tropical localities at depths between 30 and 200 meters, where cooler upwelling water and adequate nutrients existed far below the warm surface layer.
Similar findings have turned up in deep water near Morocco, Qatar, and the Philippines. Earlier explanations treated these as leftover populations from ice-age conditions, but the current understanding is that deep tropical upwelling zones actively support kelp growth today. These forests are invisible from the surface and remain largely unexplored, suggesting the total global extent of kelp habitat is significantly larger than traditional maps show.
What Controls Where Kelp Can Survive
Temperature is the single biggest factor. Kelp species vary in their tolerances, but most cannot survive prolonged exposure to water above 18 to 20°C. Some species begin to struggle above 15°C. This is why warming ocean temperatures are a direct threat to kelp forests at the warm edges of their ranges, particularly in Australia, northern California, and parts of southern Europe.
Nutrients matter almost as much. Kelp needs dissolved nitrogen from the surrounding water, and growth becomes severely limited when concentrations drop too low. Coastal upwelling, where deep, cold, nutrient-rich water rises to the surface, is what makes places like California, Chile, and South Africa so productive for kelp. During El Niño events, upwelling weakens, surface water warms, and nutrient levels plummet. Both stresses hit kelp simultaneously, and large die-offs can follow.
Kelp also requires a hard surface to attach to. Rocky reefs, boulders, and cobble provide the anchor points kelp needs. Sandy or muddy bottoms simply won’t work. This is why kelp forests tend to follow rocky coastlines rather than appearing everywhere the temperature is right. Wave exposure and water motion help too, circulating nutrients past the kelp blades and preventing sediment from smothering young plants.
The Sea Urchin Factor
Even where temperature, light, and nutrients are perfect, kelp forests can be wiped out by grazing. Sea urchins are the primary threat. In the mid-latitude belt where kelp forests are most productive, urchin populations held in check by predators like sea otters, sunflower sea stars, or lobsters allow kelp to flourish. When those predators disappear, urchin numbers explode, and the animals can mow down entire forests, leaving behind barren rocky flats sometimes called “urchin barrens.” This dynamic plays out from Alaska to Tasmania and is one of the biggest factors determining whether a given stretch of coast supports a kelp forest or not.