Kelp forests face heat, but eradication and biotech rush

Save kelp – Across warming coasts, kelp has shifted from foundation species to emergency ecology. Scientists and coastal communities are trying to rebuild these underwater forests by pairing climate-smart breeding and digital mapping with hands-on urchin eradication—work

Off British Columbia. tribal volunteers from the Haida Nation descend into coastal waters where a dense forest of rippling golden-brown kelp fronds usually looks like abundance rather than aftermath. Purple sea urchins dot the seafloor. In the visible shuffle of sunbeams under the canopy. sea lions thread through the maze. sharks glide past. and bright orange garibaldis dash between swaying fronds. The picture is breathtaking—but the task is blunt: the divers are collecting urchins as part of an eradication program.

Kelp forests are biodiversity hot spots, teeming with seaweeds, sponges, crustaceans, and other small ocean animals—many found nowhere else. At one time, vast kelp beds grew in nutrient-rich shallow waters along roughly a third of the world’s coastlines. They reduced the strength of waves, minimized coastal erosion, and provided shelter to fish, invertebrates, and marine mammals.

Today, many kelp forests are on life support. They’re harmed by water pollution from terrestrial agriculture and coastal development. bottom trawling for fish. and an explosion of kelp-devouring urchins. Yet perhaps the most important driver of kelp decline is the rapid warming of the ocean. Healthy kelp needs cool, nutrient-rich seawater. As ocean waters warm, kelp can no longer inhabit parts of its former range.

The crisis is escalating quickly. Kelp forests are vanishing twice as fast as coral reefs and four times faster than tropical rainforests. An estimated 40 percent to 60 percent of kelp forests worldwide have been lost or significantly degraded in the last 50 years. Despite the scale of those declines, kelp long received far less scientific scrutiny than higher-profile ecological crises.

In recent years. that has started to change—not just because kelp forests are stunning. but because of what they can store. A 2023 literature review of more than 180 papers on kelp’s potential to store carbon suggested that the climate benefits of these underwater forests may have been “grossly underestimated. ” according to Albert Pessarrodana. a research fellow at the University of Western Australia and the review’s lead author. In an email interview. Pessarrodana said. “Kelps are one of the fastest growing plants on the planet. ” adding that they “uptak[e] as much carbon as tropical rainforests per unit of area.”.

There’s a catch. Much of the carbon kelp captures doesn’t stay put. It ends up being released back into the marine environment as leaf litter. Kelp is a macroalgae with leaflike structures called blades, which are its organs of photosynthesis. That detritus is typically ingested by fish and other marine organisms and excreted in a matter of days. But a small percentage reaches the deep ocean, where it can remain for centuries, or even millennia. Roughly 62 million tons of carbon is carried into the deep ocean by coastal currents each year. according to two studies published in 2024.

Pessarrodana puts the problem for conservation in plain terms: “Unfortunately,” he says, “excessive warming can either kill kelps or severely curtail their growth, reducing their ability to uptake carbon.”

So the response has become layered—part intervention on the seafloor, part technology aimed at survival.

Scientists around the world are breeding new kelp varieties that they transplant as saplings into kelp habitat. The Scripps Institution of Oceanography and the San Diego Zoo have begun using artificial intelligence to digitally replicate kelp ecosystems and assess their vulnerability to climate change. Their findings are meant to help focus resources on areas most likely to be saved. Those organizations have also established a biobank to preserve kelp varieties for potential use in kelp farming and restoration projects.

At the Woods Hole Oceanographic Institution on Cape Cod, researchers are using selective breeding to develop kelp strains with a higher tolerance to warming waters. Similar efforts are underway in China and Australia.

But rebuilding underwater forests can’t wait for breeding cycles. In Australia. The Nature Conservancy’s Scott Breschkin has been working for the past year to eliminate urchins and replant beds of golden kelp on the Australia’s Great Southern Reef. an interconnected system of rocky kelp reefs spanning about 5. 000 miles of coastline across southern Australia and the island of Tasmania. The region is less famed than the Great Barrier Reef. but it is equally biodiverse. boasting thousands of species. including some still unknown to science.

As Australia’s coastal waters warm, long-spined urchins are expanding their ranges, leaving virtually lifeless urchin barrens in their wake. Breschkin warned that once the reef transitions to an urchin desert. it is “very hard to flip it back to a productive kelp habitat.” He added that urchins can persist for decades in a zombie-like state. awakening only occasionally to mow down any kelp sprouts that may appear—making recovery virtually impossible. In his view, eradicating sea urchins is a critical first step for kelp restoration.

If the seafloor is one front, the data is another. Jono Wilson, the director of ocean science for The Nature Conservancy’s California chapter, works with KelpWatch.org. The partnership of academic institutions and government agencies uses satellite imagery and drones to monitor the distribution of canopy-forming kelps along California’s Pacific coast and assess where kelp restoration efforts have been successful.

Wilson also describes the boom-and-bust cycles that historically shaped kelp forests—flourishing when conditions allow, retreating when they don’t. But recent climate-driven losses, he says, have been unprecedented. A 2013 to 2015 ocean warming event known as “the Blob” reduced kelp populations in Northern California by 95 percent.

Since 2015. water temperatures in California’s kelp forests have not dropped below 57 degrees F. a “threshold” beyond which kelp cannot thrive. Higher temperatures disrupt the kelp reproductive cycle, affecting the ability to produce viable offspring. Like corals, kelp bleaches when stressed, losing the chlorophyll that allows it to photosynthesize.

That is why the interventions around urchins are so intense: in California. kelp loss isn’t an abstract trend. it’s a living system unraveling. “Kelp provide habitat and food for thousands of species,” Wilson said. “They are nurseries for abalone and economically important fish species like cod and rockfish. They are meccas for kayakers and recreational scuba divers.” The Nature Conservancy estimates that kelp forests contribute $250 million in economic value to California annually.

In Southern California, kelp forests are faring reasonably well because the dominant species—giant kelp—grows quickly and can reach up to 200 feet tall. But purple sea urchins are wiping out kelp beds dominated by bull kelp along the coasts of Central and Northern California.

Wilson and his team are exploring ways to control those urchins. They are developing new kinds of more efficient urchin traps—round mesh devices baited with fish. They are also working with fertilizer companies to create a viable market for urchin shells. which contain calcium. nitrogen. and other plant nutrients. Ava Ocean. a Norwegian seafood firm. is currently using crushed urchin shells to produce a mineral-rich alternative to traditional bone-meal fertilizers.

There have also been attempts to support the native sunflower sea star, a voracious consumer of sea urchins. Populations of the predatory starfish. which can grow as large as a car tire. have been reduced by 90 percent since the outbreak of sea star wasting disease in 2013. Scientists recently isolated the bacterium responsible for the epidemic, giving them a better shot at helping sea stars recover. Aquariums in California and Oregon have successfully treated their affected sea stars with antibiotics. and scientists hope to learn how to breed disease-resistant sunflower starfish that can be released into the wild.

The drive to restore kelp has also reached back further in time. Since the late 1980s. there have been efforts to breed and reintroduce sea otters—another urchin predator—to coastal waters where they once flourished. Fur trade pressures in the 19th and early 20th centuries pushed otters to the edge of extinction. but they now have substantially recovered in parts of their former range. In Northern California, otters now number well over 3,000 individuals. Otters are also staging a comeback along the coast of Washington and British Columbia. Kelp forests where the otters have been released are faring noticeably better than kelp forests without otters.

Still, the scale of the work has been limited. So far, kelp restoration projects in the U.S. have been small scale, with most covering less than a hundred acres. Kyle Cavanaugh. a coastal geographer at the UCLA Institute of the Environment and Sustainability. described the bottleneck plainly: these localized projects are “very expensive and subject to zoning laws that make [them] hard to initiate.” These “localized projects need to be scaled up if we hope to turn the tide on the loss of kelp habitat.”.

Elsewhere, the tempo is faster. Kelp restoration is happening on a far larger scale in East Asia. More than half of South Korea’s kelp forests have been lost or badly degraded over the past century. Yet due to the world’s largest kelp restoration projects. South Korea now has 71. 660 acres of kelp forest. with a goal to eventually re-green 75 percent of its coastline. Farmers in South Korea harvest nearly a billion dollars worth of seaweed each year. cutting only the upper fronds and blades of the macroalgae.

Japan is also investing heavily. with more than 700 restoration projects where kelp—known as kombu—is a staple in Japanese cuisine. most commonly used in soups. Kelp’s value as a food source. and to a lesser extent as an ingredient in cosmetics. skincare products. and biodegradable packaging. may be one key reason it can keep fighting for a place in coastal futures.

But even the most effective local help faces a global constraint: emissions. Experts say that if emissions of greenhouse gases aren’t slashed. the long-term prospects of kelp and other key ocean ecosystems may be bleak. “It’s likely that we’ll see more destructive marine heat waves and warmer waters overall,” Cavanaugh said. “Beds of far less-productive turf algae will replace giant kelp and prevent it from becoming reestablished.”.

That replacement is already happening. In Maine and other coastal regions around the world. carpet-like turf algae is already replacing kelp. according to a paper published last month by the Bigelow Laboratory for Ocean Sciences in Maine. Shane Farrell. the University of Maine’s lead author. called it “a radical ecological transformation.” He also offered the kind of practical hope that conservation plans are built from: “The good news is we now understand what’s driving this shift. and this will help us predict when and where it will happen next and create different conservation strategies to combat it.”.

Back in the water off British Columbia. the Haida volunteers are still doing what they can right now: collecting urchins where the forest has begun to thin. It isn’t a substitute for cutting greenhouse emissions. But it is a bet that kelp can recover—if people can keep predators from winning the ground before heat finishes the job.

kelp forests ocean warming sea urchins restoration carbon sequestration biodiversity British Columbia Haida Nation KelpWatch.org Australia Great Southern Reef sea otters sea star wasting disease turf algae