kelp forests

What happened to the sea stars?

September 11, 2025 By EarthWise Leave a Comment

Billions of sea stars off the Pacific coast of North America from Mexico to Alaska have died from a wasting disease since 2013. This die-off is considered to be the largest ever marine epidemic. Over 90% of the population of sunflower sea stars has succumbed to the disease.

The result has been an explosion in the population of the sea urchins that the sea stars feed on. In turn, the sea urchins have devoured kelp forests that provide habitat for thousands of marine creatures. These kelp forests support a multi-million-dollar economy through fisheries and tourism as well as sequestering carbon dioxide and protecting vulnerable coastlines.

The disease begins with lesions and eventually kills sea stars by seemingly melting their tissues over a period of about two weeks. Sea stars with the disease become contorted and lose their arms.

For years, the definitive cause of the wasting disease has been elusive. But researchers from the University of British Columbia, the Hakai Institute, and the University of Washington have now identified a bacterium that is the disease-causing agent.

A strain of the Vibrio pectenicida bacteria – named FHCF-3 – is responsible. The Vibrio genus of bacteria includes pathogens that infect corals, shellfish, and even humans. Vibrio cholerae is the cause of cholera.

Research is now underway to understand the link between the disease and warming ocean temperatures due to climate change. The hope is that the discovery of the cause of the wasting disease will help guide management and recovery efforts for sea stars and impacted ecosystems.

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‘Disease detectives’ discover cause of sea star wasting disease that wiped out billions of sea stars

Photo, posted April 16, 2011, courtesy of Brian Gratwicke via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

More trouble from sea urchins

July 7, 2025 By EarthWise Leave a Comment

Sea Urchins are real troublemakers. On the West Coast, the sea urchin population exploded when the sunflower sea stars that eat them were decimated by a wasting disease. Urchins devour kelp and they ate up 96% of the region’s kelp forests. Kelp forests serve as shelter and food for a vast array of marine life and kelp sequesters as much as 20 times more carbon than terrestrial forests.

A new study by researchers at North Carolina State University looked at the health of the coral reef in Honaunau Bay on Hawaii’s Big Island and found that ballooning sea urchin populations are endangering the survival of the reef.

Fishing in these areas has greatly reduced the numbers of fish that feed on sea urchins and urchin populations have grown significantly. There are areas of the reef where there are 51 sea urchins in every square meter.

The reef is already not growing at a healthy rate as a result of water pollution and overheating created by climate change. These result in a poor environment for coral to reproduce and grow, which leaves the reef unable to keep up with the pace of erosion caused by urchins.

Reef growth is measured in terms of net carbonate production – namely the amount of calcium carbonate produced over time. In the 1980s, healthy reefs in Hawaii produced about 15 kilograms of carbonate a year per square meter. The Honaunau Reef today shows an average net carbonate production of only 0.5 kilograms per square meter. The reef is growing very slowly and can’t keep up with urchin erosion.

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Huge sea-urchin populations are overwhelming Hawaii’s coral reefs

Photo, posted October 29, 2017, courtesy of Rickard Zerpe via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

A starfish to the rescue

June 3, 2025 By EarthWise Leave a Comment

Beginning in 2013, a mysterious disease associated with a marine heatwave decimated the population of sunflower sea stars. Those huge, colorful 24-armed starfish thrived along the Pacific Coast between Alaska and Baja California. But in fairly short order, nearly six billion of the creatures perished, amounting to 94% of the global population. California lost 99% of its sea stars to the wasting disease.

The result was an ecological disaster. Sunflower sea stars are carnivorous and purple urchins are the mainstay of their diet. Without sea stars to balance the food web, the urchin population exploded. Urchins devour kelp and over the past decade, 96% of the region’s kelp forests vanished. Kelp forests serve as shelter and food for a vast array of marine life and kelp sequesters carbon as much as 20 times more than terrestrial forests.

Researchers in California and Alaska are breeding sunflower sea stars in captivity to try to produce enough of the creatures to support reintroduction. The first successful spawning of sea stars took place last year at the Birch Aquarium at San Diego’s Scripps Institution of Oceanography. But all of these are siblings, which is not a desirable breeding stock for a new population. So, they are now working with the Alaska SeaLife Center, which has the largest collection of the animals in the world. The center will provide animals to introduce genetic diversity to the growing population in captivity.

The hope is to be able to reintroduce sea stars to the Pacific region within three to five years.

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A rare, giant starfish could hold the key to restoring kelp forests on the California coast

Photo, posted November 11, 2007, courtesy of Patrick Briggs via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Otters to the rescue

February 23, 2024 By EarthWise Leave a Comment

California sea otters were hunted almost to extinction in the 19th century. Only a small number survived along California’s central coast. But over time, the otters recovered and increasingly recolonized their former habitats.

Sea otters are playing an important role in safeguarding California’s kelp forests and marshlands against the harmful effects of climate change.

Over much of the 20th century, increasing ocean heat had devastated underwater kelp forests by driving a population explosion of sea urchins that devour kelp. But sea otters eat urchins and as the sea otter population has grown, kelp has flourished. According to a new study published in PLOS Climate, the underwater kelp canopy along the central coast increased by 56% since 2016. Kelp forests have become more extensive and resilient to climate change wherever sea otters have reoccupied the California coastline.

At the same time, sea otters started recolonizing their former habitat in a central California estuary several decades ago and erosion has slowed by as much as 90%. The main reason is that otters love to eat the marsh crabs that were devouring the plants in this coastal ecosystem. The marsh plants establish dense root systems that can withstand waves and flooding. It would cost millions of dollars for humans to rebuild creekbanks and restore these coastal marshes. Instead, sea otters have been stabilizing them for free in exchange for a crab feast.

Sea otters are playful creatures that people enjoy watching. It turns out that they are also very valuable ecosystem engineers that are helping to mitigate the effects of the warming climate.

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How Sea Otters Are Protecting the California Coast Against Climate Change

Photo, posted May 17, 2021, courtesy of Michael L. Baird via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Help For Kelp | Earth Wise

April 10, 2023 By EarthWise Leave a Comment

The warming of the oceans has been causing the decimation of kelp forests. The thick canopies covering coastal ocean regions have been wilting in warmer and nutrient-poor water. Making matters much worse has been the explosion in population of sea urchins that thrive in warmer water. The urchins gobble up the kelp, often resulting in so-called urchin barrens, largely devoid of life.

Kelp are considered a foundation species that occupy nearly half of the world’s marine ecoregions. They thrive in cold water, where they form large underwater forests that provide essential habitat, food, and refuge for many species. Kelp are often harvested for use in products ranging from toothpaste and shampoo to puddings and cakes. Including the other services kelp provide, they are associated with billions of dollars in value annually.

On the North American Pacific Coast, a species of sea star consumes sea urchins. However, these creatures are critically endangered. A marine wildlife epidemic known as sea star wasting syndrome, which began 10 years ago, has killed off more than 90% of the sunflower sea star population. A new study by researchers at Oregon State University looked at the ability of sea stars to control sea urchin populations.

Lab experiments showed that sea stars consume urchins at a rate sufficient to maintain and possibly even restore the health of kelp forests. The study shows that there is a clear link between the population crash of sea stars, the explosion in sea urchin populations, and the decline in kelp.

The study’s authors are calling for active management and a coordinated sea star recovery program to try to deal with the effects of a disease whose cause has not been determined.

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Sea stars able to consume kelp-eating urchins fast enough to protect kelp forests, research shows

Photo, posted December 14, 2015, courtesy of Ed Dunens via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Vanishing Kelp Forests | Earth Wise

June 25, 2021 By EarthWise Leave a Comment

Bull kelp is the dominant species in offshore kelp forests north of Santa Cruz, California along the west coast of North America. Bull kelp has similar physical structures to terrestrial plants; it anchors to the ocean floor with root-like structures called holdfasts, and has stem-like structures called stipes from which leaf-like blades stretch out through the water, absorbing nutrients and sunshine.

These giant seaweeds form lush underwater forests in northern California’s coastal waters and have long provided critical habitat for many species like salmon, crabs, and jellyfish. But now, for much of the California coast, only a few patches of bull kelp remain.

A team from University of California Santa Cruz has studied satellite images of about 200 miles of coastline. They found that starting in 2014, the area covered by kelp has dropped by more than 95%.

The die-off was driven in part by an underwater heat wave that depleted nutrients in the water and made it harder for the kelp to grow. Making matters much worse, populations of purple sea urchins, which eat kelp, have exploded in the region because of overfishing and other reductions in urchin predators such as sea otters. The sea urchins eat kelp holdfasts, creating so-called urchin barrens where their destructive grazing has decimated kelp forests.

Bull kelp is a species at high risk of becoming endangered. In coming decades, more marine heatwaves are expected. These events as well as stronger El Niños will become more common and frequent with climate change. Between these thermal events and the sea urchins, it will be difficult for kelp forests to survive.

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Ninety-five percent of bull kelp forests have vanished from 200-mile stretch of California coast

Photo, posted October 28, 2015, courtesy of Florian Graner/Green Fire Productions via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

The Collapse of Northern California Kelp Forests | Earth Wise

March 30, 2021 By EarthWise Leave a Comment

For thousands of years, thick canopies of kelp formed an underwater forest spanning the coast of Northern California. Kelp is the cornerstone of a rich subtidal community, providing food and habitat for all sorts of marine creatures. But in recent years, a shocking transformation has occurred. Satellite imagery reveals that the area covered by kelp forests off the coast of Northern California has declined by more than 95%. Only a few small, isolated patches remain.

In a new study, researchers at the University of California Santa Cruz found that the kelp forest decline was an abrupt collapse as opposed to a gradual decline.

According to the study, which was recently published in the journal Communications Biology, kelp forests north of San Francisco were resilient to warming events in the past, like El Niños and marine heatwaves. But the decline of a key sea urchin predator – the sunflower sea star – from sea star wasting disease caused the kelp forests’ resiliency to plummet. Sea urchins are voracious consumers of kelp.

But it was a series of events – not just the sea urchins – that combined to decimate the Northern California kelp forest. A marine heatwave that became known as “the blob” developed in 2014 and moved down the West Coast in 2015. Around the same time, a strong El Niño event developed and brought warmer water up the coast from the south. The warming ocean waters combined with the ravenous sea urchin population resulted in the dramatic decline of kelp.

According to researchers, the prospects for a Northern California kelp forest recovery remain poor unless sea urchin predators return to the ecosystem.

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The collapse of Northern California kelp forests will be hard to reverse

Photo, posted August 13, 2019, courtesy of Sara Hamilton of OSU College of Science via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Native Species Or Invasive Species? | Earth Wise

February 27, 2020 By EarthWise Leave a Comment

For decades, conservation biology has characterized the movement of species into new habitats as potential invasions of alien species that pose serious dangers to local ecosystems and resident species. Wild species are classified as either native or alien. But this way of looking at the natural world is becoming increasingly controversial.

As the world warms, a mass exodus of tens of thousands of species is transforming the distribution of biodiversity. Scientists have documented countless species shifting their ranges towards the poles, higher up into the mountains, and deeper into the oceans in response to the changing climate.

Deciduous shrubs have spread into the Arctic tundra. Tropical fish have arrived in the kelp forests of the eastern Mediterranean.

A growing number of scientists now say that continuing to base conservation policy on the native-alien dichotomy may actually endanger biodiversity. The climate-driven range shifts may be the only way for many species to survive. Furthermore, only a small fraction of new arrivals may actually endanger resident species and ecosystems.

There are real distinctions between climate-displaced species and disruptive alien species introduced through global trade and travel. Among other things, climate-displaced species tend to shift their ranges alongside other species they have co-evolved with.

There is talk of establishing a Climate Change Redistribution Treaty that would create a transnational system to manage species shifting across geopolitical and biogeographical borders. The assumptions traditionally made as to which species to protect, which to leave to their own devices, and which to eradicate are no longer valid and the time has come to base conservation policies on the new reality.

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Native Species or Invasive? The Distinction Blurs as the World Warms

Photo, posted March 21, 2011, courtesy of Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Disappearing Kelp Forests

January 9, 2018 By EarthWise Leave a Comment

In recent decades, ocean temperatures in many places have warmed by nearly 3 degrees Fahrenheit. An effect of this warmer water is the decimation of what were once luxuriant giant kelp forests in eastern Australia and Tasmania. There used to be thick canopies covering much of the region’s coastal sea surface, but they have wilted in the intolerably warm and nutrient-poor water.