An Army Of ‘zombie Urchins’ Has Devastated This Underwater Forest

An Army Of ‘zombie Urchins’ Has Devastated This Underwater Forest

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Special report

California’s underwater forests have suffered a devastating decline. Now, the race is on to save them before it’s too late.

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Watch our special report on how an army of purple urchins has decimated these ecosystems, threatening the marine life that depends on them and the ocean’s ability to help fight climate change. But there is hope.

Beneath the surface of the Pacific Ocean, where the cold California current sweeps down from British Columbia, lies a hidden forest of once-astonishing beauty. Known as “the sequoias of the sea” for their rich biodiversity and carbon storing prowess, the kelp forests of Northern California were home to hundreds of marine species, including whales, seals, octopuses and sharks — until recently.

Now they’re the scene of a plague, an invasion and a mass deforestation.

A marine heat wave in 2013 set in motion a series of events that would ravage the forest and destroy the habitat for much of that sea life.

First, warm waters are thought to have helped spread a disease that devastated the population of huge sunflower starfish that lived among the kelp. Then, without this voracious predator to control their numbers, purple sea urchins spread unchecked, feasting on the kelp forest and leaving behind a barren moonscape. Just 5% of the kelp forest remains.

The drama unfolding along this coast is what experts are calling a “climate-driven catastrophe” — one example of how global warming is threatening not only the health of the ocean and the marine life within it but its ability to absorb carbon and help regulate climate change.

The loss is so alarming, it’s mobilized a coalition of researchers, non-profits, urchin divers and others in a desperate race to protect the last remaining kelp forests and rebalance the ecosystem before it’s too late.

Kelp forest locations around the world Modeled global distribution of the kelp biome

Touch and drag map to move

Kelp forests span nearly 25% of the world’s coastlines, with some of the most prolific found in the waters of South Africa, New Zealand and Australia, and along the west coast of the Americas.

“Kelp forests cover 360 million acres around the world, which is a footprint that’s five times larger than tropical coral reefs,” says Tom Dempsey, director of the California oceans program for The Nature Conservancy. “Like those coral reefs, kelp (forests) are the essential foundation for ocean health and resilience. They support a number of ecosystems and thousands of species from invertebrates to fish, seals and whales.”

Kelp is the world’s largest marine plant, reaching heights of up to 35 meters (115 feet). It flourishes in the cold, nutrient-rich waters and powerful swell of California’s famous surf. Growing up to two feet per day, it’s one of the fastest-growing organisms on Earth and one of its most productive habitats.

Research shows that macroalgae or seaweeds worldwide, including kelp, store an estimated 173 million metric tons of carbon every year — equivalent to the annual CO2 emissions of 160 coal-fired power plants — most of which is deposited in the deep sea, permanently removing it from the atmosphere and helping to fight climate change. But all is not well with the world’s kelp forests.

Areas where kelp forests have experienced decline These regions of decline represent surface canopy-forming kelp.

South AustaliaTasmaniaSouth AfricaCentral ChileSouthern NorwayNorth SeaCeltic SeaScotian ShelfGulf of MaineNorth-Central CaliforniaPuget SoundSouthern Aleutian Islands Touch and drag map to move, tap on the dots to see the locations

Hover over the dots to see the locations

Pollution, climate change and overfishing have taken their toll on kelp worldwide. Some areas are experiencing extreme losses — Tasmania has lost over 95% of its giant kelp canopy and Norway’s coast has lost 80% of its kelp in recent decades. But few places have been as badly hit as Northern California.

In 2014, a giant expanse of warm water, which had gathered off the coast of Alaska the previous year, expanded all the way down the west coast to Mexico. Nicknamed “the blob,” this marine heat wave wreaked havoc on ocean ecosystems over the following two years, spurring harmful algal blooms and killing sea life like fin whales, sea otters and salmon.

While marine heatwaves can occur naturally, research has linked “the blob” directly to human-induced global warming. Its impacts have been devastating. California’s north coast has lost approximately 95% of its kelp canopy since 2014 over a 350-kilometer (217-mile) stretch of coastline, according to a recent study by researchers at the University of California, Santa Cruz.

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KelpWatch (TNC, UCLA, UCSB; kelp data), ESRI/Maxar (imagery)

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KelpWatch (TNC, UCLA, UCSB; kelp data), ESRI/Maxar (imagery)

Kelp systems are dynamic, often impacted by storms or cyclical weather systems like El Niño. Turnover is high but those watching kelp over the past decade have noticed this is not the usual boom-and-bust cycle.

“What we’re seeing right now, particularly up on the north coast, is fundamentally different,” says Dempsey. “We are seeing a climate-driven catastrophe with massive impacts to the ecology of that system, as well as the kelp-dependent communities up in the north coast and the larger state economy.”

He estimates that the kelp forests on the northern coast of California are worth hundreds of millions of dollars a year in terms of storm protection, carbon sequestration, fisheries services and tourism. Now, they have been laid to waste by purple sea urchins.

A native species, purple urchin populations exploded after one of its last remaining predators, the sunflower starfish, succumbed to a mass die-off starting in 2013. This army of ravenous purple urchins has eaten almost all the kelp, their primary food source, and created an expanse of urchin barrens — swathes of prickly, purple orbs as far as the eye can see.

Along the whole California coast, people are experimenting with different methods for removing urchin barrens. Southern California has seen these areas expand over the past century due to overfishing and a decline in the populations of other urchin predators. When The Bay Foundation, a non-profit environmental group based in Santa Monica, first started working on its Palos Verdes site near Los Angeles, purple urchin numbers had reached up to 100 per square meter — a healthy ecosystem usually has two.

“They were everywhere, they were on top of each other,” says Heather Burdick, The Bay Foundation’s director of marine operations. “It was terrifying to swim over it because

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An army of ‘zombie urchins’ has devastated this underwater forest

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