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What happened to the sea stars?

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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

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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

Otters to the rescue

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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

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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

Sea Urchins And Climate Change | Earth Wise

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There is a thriving population of black sea urchins in bubbling volcanic vents off the coast of Ishia, a small island in the Gulf of Naples.  The oceanic environment there is very acidic, high in carbon dioxide, and very warm.   The environment represents a proxy for what is gradually happening to oceans around the world.

Researchers from the University of Sydney have determined that the ability of sea urchins to prosper in such an environment means that these animals, which are already abundant in the Mediterranean Sea are likely to spread further afield as oceans continue to warm and become more acidic.  The Mediterranean Sea is warming 20% faster than the global average.

Sea urchins are already an environmental problem in many places around the world.  When their numbers increase disproportionately, they decimate kelp forests and algae, leading to the demise of other species that depend on these things for food or shelter.  The result is something called an urchin barren, which is a rocky, sandy, urchin-filled seafloor devoid of other life.

Urchin barrens are increasingly common in many places, including the east coast of Australia and the coastline in the Americas stretching from Nova Scotia to Chile.

In Australia, for example, sea urchin populations have multiplied, and their range has expanded considerably, overgrazing kelp and damaging abalone and lobster farms.

Tests run by the Sydney researchers found that it is difficult to stress sea urchins.  They appear to tolerate conditions that other creatures simply cannot.   The only real positive is that understanding the urchins’ remarkable survival abilities might offer insights into adaptations that other animals might need in order to survive as the oceans become warmer and more acidic.

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Colonising sea urchins can withstand hot, acidic seas

Photo, posted January 31, 2010, courtesy of Anna Barnett via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Vanishing Kelp Forests | Earth Wise

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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

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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.

WAMC Northeast Public Radio

WAMC/Northeast Public Radio is a regional public radio network serving parts of seven northeastern states (more...)