Home / Science / New satellite imagery shows that northern California’s kelp forests are almost completely depleted.Here’s why.

New satellite imagery shows that northern California’s kelp forests are almost completely depleted.Here’s why.

The kelp forest eight years ago that formed a leafy ocean canopy along the Northern California coast has almost completely disappeared, and scientists studying kelp and species dependent on it worry it won’t. Can be reversed

A new study from UC Santa Cruz has found that kelp forests on the Sonoma and Mendocino coasts have decreased by an average of 95% since 2013, analyzing satellite imagery back in 1985 to determine how many factors led to their destruction. Seaweed forest The decline included an explosion of the purple urchin population, which ate it, and two ocean heat waves. Research has shown that unprecedented destruction is associated with abnormal ocean heating, and that kelp forests tend not to recover anytime soon, in part because urchins are extremely difficult to get rid of.

“They actually survive in starvation,”

; said Meredith Macpherson, a graduate student in the UC Santa Cruz Department of Ocean Sciences and co-author of the study. And there really is no seaweed forest left “

Seaweed (Nereocystis is a list.It typically thrives in the rocky shorelines of the Sonoma and Mendocino regions and creates habitat for many types of fish and invertebrates, including abalone, sea urchins, jellyfish, and snails. Its disappearance has also affected local tourism and other businesses.Abalone fishing has been closed to recreational divers since 2018, and Mendocino County’s commercial red urchin fish has almost shut down. all


Two warm-water incidents that helped deplete the kelp forests – El Niño and the so-called “warm water droplets” co-occurring from 2014 to 2016. During the same period, wasting disease attacked populations of sea stars. Sunflower A purple sea urchin without a predator

Those hedgehogs quickly took over, eating leftover seaweed and starved two other types popular with divers and sushi lovers – red abalone and red sea urchin. (Purple Hedgehogs are not commercially viable) What remains are called the Hedgehog Cemetery, a rocky area covered with spiky purple invertebrates throughout hundreds of kilometers of the north coast.

“What we saw in Northern California was relatively unprecedented in terms of size,” said Tristin McHugh, director of the Nature Conservancy’s California Oceans program, which is developing a pilot method for removing purple sea urchins and restoring them. Seaweed

There were fears, though, another warm drop of water formed last year outside Alaska. But the water temperature in the north coast has returned to normal, McPherson said, but the cow seaweed has not recovered. Unlike other kelp species native to California, it is an annual species that dies in winter when it is washed ashore in a long, brownish-brown tube-like mound with a bulbous tip. Usually each spring is returned.

Scientists have been monitoring the decline of kelp forests for years with aerial imagery and tide data. But the new study is the first to use satellite imagery to more closely analyze changes in growth, along with ocean temperatures and nutrient levels.

“We can easily see kelp from space using satellites,” McPherson said.

The growth of kelp depends on the cool habitat in the spring, which brings nutrients to the surface and decreases as the water temperature rises. Although the previous El Niño event – a natural pattern that raised the water temperature in the Pacific Ocean for a year or two But also resulted in the reduction of seaweed But it is often recoverable as well

A sea urchin from the Norwegian company Urchinomics, which is launching sea urchins.
Sea urchin farm from the Norwegian company Urchinomics, which is opening a farm. Sea urchin “ranch” in Bodega BayUrchinomics

What was different from 2014-16 was the explosion of purple sea urchins and the addition of warm water droplets, which at their peak raised ocean temperatures almost 7 degrees above the average. While there is some evidence that the drops are linked to climate change. But more importantly, the sea heat wave intensifies as global temperatures rise due to climate change, McPherson said.

Climate change, pollution and other factors have also been blamed for declining global kelp forests over the past 20 years, but in California it is the worst on San Francisco’s north coast. Monterey Bay and other parts of central California have lost their algae forests to barren sea urchins. But those areas are a blend of bovine and giant seaweed, and there are also sea otters that help hunt hedgehogs. In southern California, where giant kelp is the main species, the forests are still better.

The most relevant part about the Sonoma-Mendocino seaweed forest decline is that unless sea stars, sunflowers, or other predators return, the purple sea urchins show no signs of shifting.

“Typically, some physical disturbances or diseases will wipe out populations,” McPherson said. “It can go on for decades and even decades.”

The loss of their habitat to purple sea urchins was the reason the California Department of Fisheries and Wildlife in 2018 stopped fishing for red abalone for five years, often taking recreational divers from. Across California to the north coast As a result, the last dive shop in the area closed in Fort Bragg about a year ago.

Many off-job professional sea urchins have been employed in a state-sponsored program managed by the non-profit Reef Check to manually remove purple urchins from the seafloor. It’s a slow process. In some cases, there were as many as 20 to 30 sea urchins per square meter, and similar efforts in Norway, Japan and New Zealand have shown a reduction to 2 per square meter needed for the kelp forests to recover, McHugh said.

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