A decade long mystery - why were billions of starfish turned to goo?

Short summary

In this Science Weekly episode, host Madeleine Finlay discusses the devastating sea star wasting disease with Dr. Melanie Prentice. Beginning in 2013 off Vancouver, the outbreak spread along the West Coast from Mexico to Alaska, killing billions of sea stars and driving the sunflower sea star toward extinction. The disease triggered ecological cascades, notably urchin population explosions that overgrazed kelp forests, threatening fisheries, tourism, and coastal protection. After more than a decade of investigation, researchers identified a bacterium, Vibrioectinoya, as the causative agent, with warmer waters likely enhancing its replication. Using controlled lab challenges and comprehensive genomic analyses, they confirmed causation and outlined future steps, including diagnostics and strategies to bolster resilience. The episode highlights the link between climate change, marine disease, and coastal ecosystems, and underscores the importance of credible science in guiding recovery efforts.

Overview: Sea Stars as Keystone Players

Sea stars, especially the sunflower sea star, are ancient marine invertebrates and crucial predators on the seafloor. Sunflower sea stars can reach about 1 meter in diameter and bear up to 24 arms, moving across the ocean floor like robot vacuums in search of prey. They are broadcast spawners and can feed on a wide range of organisms, including mussels, clams, and sea urchins. Their vibrant colors and soft bodies make them iconic along the Pacific coast. Importantly, sea stars are keystone species, meaning their presence or absence has a disproportionate effect on ecosystem structure and function. Their decline reverberates through kelp forests, urchin populations, and the communities that rely on these habitats for fisheries and tourism.

The Outbreak: A Coastwide Catastrophe

The story begins in 2013 in Vancouver, British Columbia, with a mysterious wasting disease that rapidly spread along the West Coast, from Mexico to Alaska, within a few short years. The epidemic decimated billions of sea stars, with the sunflower sea star suffering precipitous losses—more than 90% of its population collapsed in a few years. This sudden fall rippled through the ecosystem: sea urchin numbers surged in the absence of sunflowers to prey on them, and urchins grazed kelp forests, transforming biodiverse kelp ecosystems into barren landscapes known as urchin barrens. The collapse of kelp forests had broad consequences, eroding biodiversity and undermining local economies tied to fishing and tourism, while also diminishing coastal protection and carbon sequestration functions of kelp itself. Northern California, for example, saw dramatic losses in kelp forests, underscoring the scale of ecological and economic disruption.

"Sea stars are keystone species, which basically means that they have this disproportionately strong impact on the ecosystems that they inhabit." - Dr. Melanie Prentice

Beyond the ecological consequences, kelp forests play critical roles in filtering water, producing oxygen, stabilizing sediments, and supporting coastal economies. The episode situates the tragedy within a broader context of climate-driven changes in marine ecosystems and illustrates how the disappearance of a single group of predators can trigger cascading effects across entire habitats.

Solving the Mystery: A Pathogen Identified

For more than a decade, scientists labored to identify the cause of sea star wasting disease. The breakthrough came from using controlled challenge experiments, where healthy sea stars were exposed to the disease under careful laboratory conditions, allowing researchers to observe the full progression of illness from onset to death. Researchers then generated large genomic datasets to compare the microbial communities in wasting versus healthy stars. This comparative approach revealed a bacterium with high abundance in diseased individuals, particularly in the sea star's saline fluid, the hemolymph-like blood of echinoderms. To conclusively establish causation, the team isolated the bacterium in pure culture and demonstrated that it could induce wasting disease on its own when introduced to healthy individuals. The pathogen was identified as vibrioectinoya, a Vibrio species known to thrive in warmer waters, aligning with observed seasonal patterns of outbreaks. The discovery marked a turning point, shifting the narrative from mystery to a tangible agent behind the disease and opening avenues for diagnostics and intervention.

"There was certainly like this kind of pause where we're all just looking at each other like, is this, is this even possible?" - Dr. Melanie Prentice

Vibrioectinoya is not unique in its family; many Vibrio species cause disease in marine organisms and some human pathogens as well. Its apparent success in warmer waters suggests that rising ocean temperatures may amplify outbreaks by boosting pathogen replication and potentially compromising host immunity. The researchers emphasize that temperature likely interacts with disease dynamics, creating conditions under which epidemics become more frequent and severe. This climate-linked vulnerability underscores the need to monitor pathogen presence, study host resistance, and adapt management strategies as oceans continue to warm.

Pathogen, Temperature, and the Climate Link

The identification of vibrioectinoya sits at the nexus of disease ecology and climate change. Warmer waters can enhance pathogen growth and may stress hosts, reducing their ability to allocate resources to fight infections. The team suggests that both pathogen success and host vulnerability—driven by ephemeral heat and other environmental stressors—likely contribute to the observed seasonality and intensity of wasting disease outbreaks. This understanding reframes conservation strategies, highlighting the importance of monitoring pathogen dynamics in relation to temperature trends to anticipate and mitigate future outbreaks.

What Comes Next: Diagnostics, Resilience, and Restoration

With the causative agent identified, researchers are pursuing practical tools to support conservation. A major goal is developing diagnostic assays that can detect the presence of vibrioectinoya in wild populations, enabling more informed decisions about translocations, reintroductions, and management actions. Scientists are also investigating whether some sea star populations or individuals show innate or acquired resistance to the disease, with the aim of selectively breeding or prioritizing resilient individuals for restoration efforts. Understanding the pathogen's mechanisms remains a priority, as insights into how vibrioectinoya causes wasting could inform treatments and interventions that reduce environmental impact. The consensus is clear: identifying the pathogen is a critical first step toward rehabilitating affected ecosystems and reviving keystone species like the sunflower sea star.

"There are so, so many questions left to answer." - Dr. Melanie Prentice

Hope, Community, and the Road Ahead

The episode concludes on a note of cautious optimism. While the disease has caused profound ecological disruption, the identification of vibrioectinoya provides a concrete target for diagnostics and restoration strategies. The sunflower sea star remains a symbol of resilience for researchers and coastal communities, and the work underway—diagnostics, resilience screening, and ecological restoration—offers a path toward recovery of sunflower sea stars and the broader ecosystems they shape. The podcast emphasizes credible, science-based storytelling and collaborative research as essential drivers of conservation, reminding listeners that protecting keystone species requires sustained effort, interdisciplinary collaboration, and adaptive management in the face of a warming, changing ocean.