Blood stars (top left) and leather stars (top right) were less impacted by the disease and are more likely to be seen today. Sunflower sea stars (bottom left), mottled sea stars (lower center, this one showing symptoms of disease) and ochre sea stars (lower right) used to be common, but were most affected by the disease and have become more rare. (Photos courtesy of Mandy Lindeberg, NOAA, and Brenda Konar, University of Alaska Fairbanks)

Refuge Notebook: The fall of sea stars

Sea stars are a keystone species. As a top predator, they can restructure intertidal communities. For example, by feeding on mussels, they open up limited “real estate” in the intertidal zone for other species to move in.

Sea stars, like other intertidal species, can tolerate extreme conditions such as the pounding of waves, heat and desiccation when exposed during low tide. However, the unusually warm waters during the 2014 to 2016 marine heatwave may have facilitated the spread of sea star wasting syndrome and caused sea star populations in the northern Gulf of Alaska to crash beginning around the same time.

The recent sea star die-off event began in the Eastern Pacific Ocean, or the West Coast, in 2013 and hit Alaska in 2014. In the warm ocean waters, the disease expanded. This event impacted 20 species of sea stars from Mexico to Alaska and decimated many sea star populations across the northern Gulf of Alaska.

Symptoms of sea star wasting syndrome include abnormally twisted arms, white lesions, deflation of arms and body, arm loss, and body disintegration. Death occurs over the course of days to weeks.

Currently, the disease is thought to result from an imbalance in the sea star’s microbiome (microorganisms in a particular environment), combined with environmental stress, such as extreme heat and low oxygen. A proliferation of bacteria on the surface of sea stars leads to reduced oxygen, which essentially causes the star to suffocate.

Decaying stars exacerbate the situation by providing even more organic material for the bacterial communities to flourish. Impacts vary by species and site conditions and there is still a lot to learn as more information becomes available.

Much of what we know about the effects of the disease in the Northern Gulf of Alaska stem from our long-term nearshore monitoring activities there. The Gulf Watch Alaska program, a consortium of agency and university cooperators, conducts surveys at multiple rocky intertidal sites in four regions: Western Prince William Sound, Kenai Fjords National Park, Kachemak Bay, and Katmai National Park and Preserve.

Based on our observations, prior to the die-off, sea stars were abundant in the Northern Gulf of Alaska and exhibited high species diversity across regions, largely due to differences in fetch, tidal range and the proximity of tidewater glaciers in each location.

While it appears that the disease has abated, the density and diversity of sea stars remains low at our monitoring sites. The precipitous loss of some species reduced the species diversity that once existed across regions, making these once-unique sea star communities more similar across the Northern Gulf of Alaska.

We found that species composition is now more closely correlated with the slope of the shore, fetch and tidal range, which may be a reflection of the surviving sea star species being less influenced by tidewater glaciers (freshwater melting) and more strongly influenced by slope (desiccation).

Sea star species that are currently present are those that were not impacted by sea star wasting syndrome. In 2020, the sea star species thought to be unaffected by the disease continued to be present (primarily blood star and leather star).

The once dominant sea stars that were killed by the disease continue to be rare or absent (primarily sunflower star, mottled star and ochre star). Areas in Alaska devoid of sea stars for multiple years have enabled prey species, such as mussels, to flourish.

As sea stars were lost from the system, we began to watch how other species in these intertidal communities responded to changes in the predator population. What we continue to learn from the sea star die-off helps us understand intertidal communities, the species that thrive there, and the environmental variables that influence them.

This article builds on the collective efforts of Gulf Watch Alaska, Nearshore Component ( Collaborators include Dr. Sarah Traiger of the U.S. Geological Survey and other scientists from National Park Service, USGS, University of Alaska Fairbanks, National Oceanic and Atmospheric Administration and Coastal Resources Associates, Inc.

This article is based on a journal article, “Wasting disease and static environmental variables drive sea star assemblages in the Northern Gulf of Alaska,” by Dr. Brenda Konar at UAF and others, which appeared in the Journal of Experimental Marine Biology and Ecology in November 2019.

Heather Coletti is a marine ecologist with the National Park Service Southwest Alaska Inventory & Monitoring Network. Marine and coastal ecosystem research and monitoring is conducted by a collaboration of many agencies, organizations, and volunteers. This article presents our collective work. Find more Refuge Notebook articles (1999–present) at


For the Clarion

More in Sports

Anthony Botello fishes for halibut off the coast of Homer, Alaska, on Sept. 6, 2021. (Camille Botello)
Out of the Office: Fish on!

I was pretty spoiled as a kid. The chest freezer in our… Continue reading

The Kenai Central High School women’s cross country team finishes in second place with 58 points at Bartlett High School in Anchorage, Alaska on Saturday, Oct. 9, 2021. (Camille Botello/Peninsula Clarion)
Boonstra repeats as Division II champ

Kenai Central’s Jayna Boonstra raced her way to another Division II state… Continue reading

Sports in brief

Volleyball Upcoming meets: TBA Thursday, Oct. 14: Varsity Volleyball at Juneau Tourney… Continue reading

Olympic gold medalist Lydia Jacoby waves to the crowd in Seward during her celebratory parade on Thursday, August 5, 2021. (Ashlyn O’Hara/Peninsula Clarion)
Jacoby nabs two 2nds at World Cup

Lydia Jacoby, a 17-year-old senior at Seward High School, finished second in… Continue reading

Homer, Soldotna notch volleyball wins

The host Homer volleyball notched a 3-0 Southcentral Conference victory over Nikiski… Continue reading

Nikiski's Savanna Stock receives serve against Anchorage Christian Schools on Friday, Oct. 1, 2021, at Nikiski High School in Nikiski, Alaska. (Photo by Jeff Helminiak/Peninsula Clarion)
Volleyball roundup: Homer beats GC and ACS

Homer 3, Grace Christian 0 The host Mariners quickly rebounded from their… Continue reading

Sports in brief

Cross Country Upcoming meets: Noon Saturday, Oct. 9: Cross Country at State… Continue reading

Kenai Central's Brooke Ashley and Homer's Nevaeh Diaz tangle at the net at Kenai Central High School on Thursday, Sept. 30, 2021, at Kenai Central High School. (Photo by Jeff Helminiak/Peninsula Clarion)
Kenai, Seward get 5-set wins

The host Kenai Central volleyball team pulled off a massive comeback to… Continue reading

Author Kathleen Sorensen (252) and the rest of the field take off from the starting line at the Kenai River Marathon on Sunday, Sept. 26, 2021, in Kenai, Alaska. (Photo by Jeff Helminiak/Peninsula Clarion)
Tangled Up in Blue: Three halves

I ran my third Kenai River Half Marathon this weekend. I remember… Continue reading

Most Read