The Forests We Never See
Most people picture forests as places of towering trees, bird calls, and dappled light. But some of Earth's most productive and ecologically vital forests grow underwater, reaching heights of 30 to 60 metres from the seafloor, swaying in ocean currents, and forming ecosystems that support thousands of species. Kelp forests — dominated by large brown algae of the genus Macrocystis, Nereocystis, and related species — are among the most biodiverse habitats on the planet, comparable in ecological complexity to tropical rainforests.
They are also disappearing. According to research published in the journal Science Advances, kelp forests have declined by an estimated 40% globally over the past half century. In some regions — including large stretches of the Australian, Norwegian, and Californian coastlines — losses exceed 90%. The primary driver is climate change, operating through warming ocean temperatures, marine heatwaves, and the proliferation of kelp-eating sea urchins whose predator populations have collapsed.
What Kelp Does for the Planet
Kelp forests are not merely beautiful — they are functionally critical to the health of the ocean and, by extension, to the global climate system. Through photosynthesis, kelp absorbs carbon dioxide and produces oxygen at extraordinary rates. Research from Woods Hole Oceanographic Institution estimates that kelp and other macroalgae may sequester as much as 173 million tonnes of carbon per year globally — a figure comparable to the annual emissions of many mid-sized industrial nations.
The ecological services extend far beyond carbon sequestration. Kelp forests provide nursery habitat for fish species that support major commercial fisheries. They shelter marine mammals, including sea otters, seals, and grey whales. They physically buffer coastlines from wave erosion, reducing the damage caused by storms and the long-term effects of sea-level rise. A healthy kelp forest is, in the most literal sense, coastal infrastructure.
The Threat: Warming Waters and the Urchin Barrens
Kelp is exquisitely sensitive to water temperature. Most species cannot survive sustained temperatures above 20–22°C, and the warming trend driven by climate change is pushing sea surface temperatures in many kelp habitat zones past those thresholds. The National Oceanic and Atmospheric Administration (NOAA) has documented a significant increase in the frequency and intensity of marine heatwaves — extended periods of anomalously warm ocean temperatures — which can cause mass kelp die-offs within weeks.
The collapse of kelp predator populations has compounded the problem dramatically. Sea otters, which historically controlled urchin populations along the Pacific coast, were hunted to near extinction during the fur trade. Without sufficient predation, urchin numbers explode, and urchins in their "zombie" state — starving but surviving — bulldoze through kelp holdfasts, consuming everything in their path and leaving behind barren seafloor. These "urchin barrens" now cover large areas of seafloor that once supported thriving kelp ecosystems.
The Global Restoration Race
Scientists and conservation organisations around the world are working urgently to restore kelp forests before the losses become irreversible. The approaches range from the intensely practical to the technologically ambitious.
In Norway, researchers at the SINTEF research institute have developed large-scale kelp aquaculture methods that can produce millions of juvenile plants for ocean seeding. In California, organisations like The Kelp Forest Foundation and The Nature Conservancy are running coordinated urchin culling programmes — manually removing urchins from specific reef areas to allow kelp recovery. In Tasmania, where 95% of the giant kelp forest has been lost, a consortium of universities and government agencies is selectively breeding heat-tolerant kelp strains capable of surviving the warmer waters that are now the regional norm.
Technology is also playing a growing role. Autonomous underwater vehicles are being used to map kelp extent and health in real time, providing the monitoring data needed to target restoration efforts efficiently. Satellite imagery and machine learning algorithms allow researchers to track canopy coverage across entire coastlines — work that would have taken decades of manual surveying a generation ago. The Global Kelp Initiative coordinates these efforts internationally, sharing data and best practices across the research community.
Kelp as a Climate Solution
Beyond its ecological value, kelp is attracting serious attention as a scalable climate solution. Proposals for large-scale offshore kelp farming — growing kelp specifically to sequester carbon and then sink the biomass to the deep ocean — have been put forward by researchers at institutions including the Scripps Institution of Oceanography and the Imperial College London. If implemented responsibly, such approaches could remove significant quantities of atmospheric CO₂ while also providing biomass for biofuels, food, and agricultural fertiliser.
The economics of kelp farming are also improving. Kelp is used commercially in food (seaweed salads, sushi wraps), cosmetics, pharmaceuticals, and increasingly as a packaging alternative to single-use plastics. As demand grows and cultivation technology matures, the commercial case for kelp investment strengthens — creating economic incentives that align with conservation goals.
Why It Matters to All of Us
The decline of kelp forests is a crisis that unfolds mostly out of sight, beneath waves that most of us will never look beneath. But its consequences are not invisible. The fish that kelp nurseries shelter feed hundreds of millions of people. The carbon that kelp sequesters would otherwise warm the atmosphere further. The coastlines that kelp buffers are home to billions of people and trillions of dollars of infrastructure.
Saving kelp forests requires reducing the emissions that are warming the oceans — there is no technical fix for a problem rooted in global temperature rise. But alongside mitigation, the restoration work underway represents some of the most promising environmental recovery efforts on Earth. For more, explore the work of Global Kelp Initiative, Kelp Forest Foundation, and NOAA's Ocean Service.