Kelp forests grow along roughly 25 percent of the world’s coastlines, concentrated in cool, nutrient-rich waters across both hemispheres. They thrive from subarctic Alaska to the southern tip of South America, around southern Australia, along the coasts of South Africa, and throughout northern Europe. If you picture a map of the world’s temperate and polar coastlines, kelp forests line most of them.
The Pacific Coast of the Americas
The eastern Pacific holds the largest and most well-known kelp forests on Earth. They stretch continuously from Alaska and western Canada down through California and into Baja California, Mexico. Two dominant species split this range. Bull kelp dominates the colder northern waters from Alaska through northern California. Giant kelp, the species most people picture when they think of kelp forests, takes over from central California southward into Baja. Alaska’s waters actually support three distinct types of kelp, making it one of the more diverse kelp regions in the Northern Hemisphere.
On the South American side, kelp forests run along the Pacific coasts of Peru, Chile, and around the tip of the continent. Chilean kelp species currently span from about 14°S latitude down to 42°S, covering thousands of kilometers of coastline.
Australia’s Great Southern Reef
Australia’s kelp system is massive but far less famous than its tropical coral reefs. The Great Southern Reef stretches from Kalbarri in Western Australia, sweeps around the entire rugged southern coast, and extends up into northern New South Wales on the east side. Dense kelp forests fuel the productivity of this reef system, making it one of the most biodiverse temperate marine ecosystems in the world. Despite its scale, the Great Southern Reef receives a fraction of the attention and protection that the Great Barrier Reef does.
South Africa’s Atlantic Coast
South Africa is home to distinctive kelp forests dominated by giant bamboo kelp, a species restricted to the southern Atlantic. These forests are concentrated around the Cape Town region and extend along the western coast. The kelp forests near Cape Town were among the most intensively studied in the world during the late 1970s and 1980s, though forests farther north along the west coast and east past Hermanus remain relatively poorly explored.
Northern Europe and the Arctic
Kelp forests extend across the coastlines of Norway, the British Isles, Iceland, and into Arctic waters around Svalbard and Greenland. Cold-adapted species like sugar kelp tolerate water temperatures as low as negative 1.5°C, allowing them to colonize surprisingly high latitudes. In Svalbard, kelp grows down to 18 to 20 meters deep, while some fjords support growth beyond 25 meters. Greenland’s kelp forests are particularly notable: in the clear offshore waters of Disko Bay, researchers have documented kelp growing deeper than 61 meters, a record for high-latitude regions.
Surprising Tropical Locations
Kelp forests aren’t strictly a cold-water phenomenon. Researchers have predicted and then confirmed the existence of submerged kelp habitats in tropical regions between the Tropics of Cancer and Capricorn, growing at depths of 30 to 200 meters where the water is cool enough. Deep-water diving expeditions have documented extensive kelp forests in at least eight tropical localities, and similar deep-water kelp populations exist around Morocco, Qatar, and the Philippines. These are likely remnants of shallow-water populations that thrived during ice ages when ocean temperatures were lower. They survive today by growing far below the warm surface layer.
What Kelp Forests Need to Grow
Three conditions determine whether kelp can establish in a given location: water temperature, light, and a hard surface to grip.
Temperature is the primary constraint. Most kelp species need water below about 21 to 24°C to survive. Giant kelp, for example, hits its upper limit for spore development between roughly 22 and 24°C. Sugar kelp can tolerate slightly warmer conditions, surviving up to 23°C, but its photosynthetic performance drops sharply above 15°C. These temperature ceilings explain why kelp forests are absent from most tropical surface waters.
Light limits how deep kelp can grow. Most kelp forests worldwide extend to maximum depths of 30 to 40 meters, with forests in Alaska, Canada, and Norway typically reaching 20 to 30 meters. The exceptionally deep kelp in Greenland’s Disko Bay exists because the water there is remarkably clear, with enough light for photosynthesis penetrating to 67 meters deep. In murkier coastal waters where plankton blooms absorb more light, kelp forests are confined to shallower zones.
Kelp also requires a hard seafloor to anchor its holdfast, the root-like structure that grips the bottom. Rocky reefs, granite, limestone, and other solid substrates all work. Surface roughness matters: textured rock gives young kelp better grip because tiny root-like structures can interlock with microscopic crevices. Holdfasts can actually penetrate bedrock, boring up to 1.5 millimeters into granite and 4 millimeters into softer limestone. Sandy or muddy bottoms won’t support kelp forests, which is why long stretches of coastline with the right temperature and light still lack kelp.
How These Ranges Are Shifting
Ocean warming is pushing kelp forests toward the poles. At the warm edges of their ranges, kelp is disappearing as water temperatures climb past survival thresholds. At the cool edges, kelp is colonizing newly ice-free coastlines. The net effect, though, is a loss. Modeling of two South American kelp species projects that both will lose more than 50 percent of their current range within the next 50 years. One species currently spanning about 17 degrees of latitude could shrink to a refuge zone of just 6 degrees, while gaining only a sliver of new territory at its southern edge.
This pattern is playing out globally. Kelp forests in northern Australia, southern Japan, and parts of the Mediterranean are contracting as warm-water species move in to replace them. Meanwhile, Arctic regions like Svalbard and Greenland are seeing kelp expand into areas that were previously locked under seasonal ice. The geography of kelp forests is not fixed; it’s actively being redrawn by rising ocean temperatures.