In British Columbia’s coastal waters, Haida Nation tribal volunteers are diving for purple sea urchins within a lush forest of golden-brown kelp fronds. Sunlight filters through the canopy, casting a captivating play of light and shadow, while rays and sea lions navigate the kelp maze, sharks glide by, and vivid orange garibaldis dart among the swaying fronds.
Kelp forests are known as biodiversity hotspots, brimming with a vibrant array of seaweeds, sponges, crustaceans, and other unique marine life. Historically, extensive kelp beds thrived in nutrient-rich shallow waters along roughly a third of the world’s coastlines. These beds played a crucial role in reducing wave strength, minimizing coastal erosion, and providing refuge for fish, invertebrates, and marine mammals.
Currently, many kelp forests face severe threats due to water pollution from land-based agriculture and coastal development, bottom trawling for fish, and a surge of kelp-eating urchins, which the Haida volunteers are targeting in an eradication effort. However, the most significant factor in kelp decline is the rapid warming of ocean waters.
Kelp forests require cool, nutrient-rich seawater to thrive. As ocean temperatures rise, kelp can no longer survive in parts of their historical range. The situation is deteriorating rapidly, with kelp forests disappearing at twice the rate of coral reefs and four times that of tropical rainforests. An estimated 40 to 60 percent of kelp forests worldwide have been lost or significantly degraded over the past 50 years. Despite less scientific attention compared to other ecological crises, kelp is gaining recognition for its carbon sequestration potential in coastal ecosystems.
A 2023 review of over 180 studies examined kelp’s carbon storage potential, suggesting the climate benefits of these underwater forests may be “grossly underestimated,” according to Albert Pessarrodana, a research fellow at the University of Western Australia and the review’s lead author. “Kelps are among the fastest-growing plants on Earth,” he noted in an email interview, “absorbing as much carbon as tropical rainforests per unit area.”
A significant portion of the carbon sequestered by kelp is reintroduced into the marine environment as leaf litter. Kelp, a macroalgae, has leaflike blades that conduct photosynthesis. This detritus is usually consumed by marine organisms and excreted within days. Nevertheless, a small fraction reaches the deep ocean, where it can remain for centuries, or even millennia. Coastal currents transport approximately 62 million tons of carbon into the deep ocean annually, according to two studies published in 2024.
Pessarrodana warns, “Excessive warming can either kill kelps or severely limit their growth, reducing their capacity to absorb carbon.”
To combat this decline, scientists worldwide are developing new kelp varieties and planting them as saplings in kelp habitats. The Scripps Institution of Oceanography and the San Diego Zoo are utilizing artificial intelligence to digitally model kelp ecosystems and evaluate their climate change vulnerability. The organizations have also established a biobank to conserve kelp varieties for potential use in farming and restoration projects. At the Woods Hole Oceanographic Institution on Cape Cod, researchers are using selective breeding to create kelp strains with greater tolerance to warming waters. Similar initiatives are ongoing in China and Australia.
Scott Breschkin from The Nature Conservancy has been working for a year to eradicate urchins and restore golden kelp beds on Australia’s Great Southern Reef. This interconnected system of rocky kelp reefs covers about 5,000 miles of coastline across southern Australia and Tasmania. While less renowned than the Great Barrier Reef, it is equally rich in biodiversity, with thousands of species, some still unknown to science.
As Australia’s coastal waters warm, long-spined urchins are expanding their ranges, leaving barren urchin deserts behind. “Once the reef becomes an urchin desert, reverting it to a productive kelp habitat is challenging,” Breschkin explained, noting that urchins can persist for decades in a dormant state, occasionally awakening to consume any new kelp growth, making kelp forest recovery nearly impossible. Eradicating sea urchins, he asserts, is a crucial first step for kelp restoration.
Jono Wilson, director of ocean science for The Nature Conservancy’s California chapter, collaborates with KelpWatch.org, a coalition of academic institutions and government agencies using satellite imagery and drones to monitor canopy-forming kelps along California’s Pacific coast and evaluate the success of restoration efforts. Wilson notes that these undersea forests experience boom-and-bust cycles, thriving and retreating as ecological conditions shift. However, climate-driven losses recently have been unprecedented. An ocean warming event from 2013 to 2015, known as “the Blob,” reduced kelp populations in Northern California by 95 percent.
Since 2015, California’s kelp forest water temperatures have not fallen below 57 degrees F, a critical threshold for kelp survival. Warmer temperatures disrupt kelp reproduction, affecting their capacity to produce viable offspring. Like corals, stressed kelp undergoes bleaching, losing the chlorophyll needed for photosynthesis.
Kelp diebacks transform ecosystems. “Kelp provides habitat and food for thousands of species,” says Wilson. “They serve as nurseries for abalone and economically significant fish species like cod and rockfish. They attract kayakers and recreational scuba divers.” The Nature Conservancy estimates that kelp forests contribute $250 million in economic value to California each year.
While Southern California’s kelp forests are relatively stable — with giant kelp, the dominant species, growing rapidly and reaching up to 200 feet — bull kelp beds along Central and Northern California’s coasts are being decimated by purple sea urchins. Wilson and his team are exploring ways to manage these urchins, developing more efficient traps — round mesh devices baited with fish — and collaborating with fertilizer companies to create a market for urchin shells, which contain valuable nutrients like calcium and nitrogen. Norwegian seafood firm Ava Ocean is already using crushed urchin shells to produce a mineral-rich alternative to traditional bone-meal fertilizers.
Efforts are also underway to support the native sunflower sea star, a prolific sea urchin predator. Populations of this predatory starfish, which can grow as large as a car tire, have declined by 90 percent since the 2013 outbreak of sea star wasting disease.
Scientists have recently identified the bacterium responsible for the epidemic, improving their chances of aiding sea star recovery. Aquariums in California and Oregon have successfully treated affected sea stars with antibiotics, and scientists are hopeful about breeding disease-resistant sunflower starfish for release into the wild.
Since the late 1980s, efforts have been made to breed and reintroduce sea otters, another urchin predator, to coastal waters where they once thrived. Having been driven to the brink of extinction by the fur trade in the 19th and early 20th centuries, otters have significantly rebounded in some parts of their former range. Over 3,000 otters now reside in Northern California, and they are also making a comeback along the coasts of Washington and British Columbia. Kelp forests with reintroduced otters are faring noticeably better than those without otters.
Kelp restoration projects in the U.S. remain small, with most covering less than a hundred acres. These projects are “very expensive and subject to zoning laws that complicate their initiation,” says Kyle Cavanaugh, a coastal geographer at the UCLA Institute of the Environment and Sustainability. “Scaling up these localized projects is essential if we aim to reverse the loss of kelp habitat.”
In East Asia, kelp restoration is occurring on a much larger scale. Over half of South Korea’s kelp forests have been lost or severely degraded over the past century. However, thanks to the world’s largest kelp restoration initiatives, the nation now has 71,660 acres of kelp forest, with a goal to restore 75 percent of its coastline. South Korean farmers harvest nearly a billion dollars’ worth of seaweed annually, cutting only the upper fronds and blades of the macroalgae. Japan has over 700 restoration projects, where kelp, known as kombu, is a staple in Japanese cuisine, primarily used in soups.
Kelp’s role as a food source, and to a lesser extent as an ingredient in cosmetics, skincare products, and biodegradable packaging, may be crucial for its survival. However, experts warn that without a significant reduction in greenhouse gas emissions, the long-term outlook for kelp and other essential ocean ecosystems could be grim. “We are likely to witness more destructive marine heat waves and overall warmer waters,” says Cavanaugh. “Less-productive turf algae will replace giant kelp and hinder its reestablishment.”
In Maine and other coastal areas worldwide, turf algae is already supplanting kelp, as reported in a recent paper by the Bigelow Laboratory for Ocean Sciences in Maine. This represents “a radical ecological transformation,” according to Shane Farrell, the study’s lead author. “The good news is we now understand what’s driving this shift, allowing us to predict when and where it will occur next and craft different conservation strategies to address it.”
