After a decade of confusion, an international group of scientists points to a bacterium of the genus Vibrio as the main cause of the mass die-off of sea stars in the northeast Pacific, an episode that transformed millions of individuals into gelatinous waste in a matter of days.
The disease, known as starfish wasting syndrome (SSWD/SSWS), extended from Alaska to Baja California and affected more than 20 species; estimates exceed 5.000 billion casualties, with the sunflower starfish as the emblematic victim.
What is known about the outbreak?
Since 2013 they have been documented skin lesions, arm twisting and limb detachment which lead to rapid tissue decomposition in about two weeks.
The most affected species is Pycnopodia helianthoides (sunflower starfish), whose population plummeted by around 90% in the early years of the episode, with cascading impacts on the coastal ecosystem.
The pathogen under the microscope
The study identifies Vibrio pectenicida —a relative of the cholera bacteria— as responsible for the condition; specifically, a strain called FHCF-3 which triggers tissue degradation.
Vibrio is a widely distributed bacterial group that causes problems in corals and mollusks; the strain found in starfish has not been linked to human infections since its description in the 1990s.
The work, published in Nature Ecology & Evolution, provides evidence that resolves a question that has been open for years, according to marine microbiologists who did not participate in the research.
The investigation: from false trail to discovery
After multiple hypotheses, including a densovirus Initially proposed, experiments failed to consistently reproduce that viral cause, and molecular tests they discarded it.
The twist came when analyzing the coelomic fluid —liquid that bathes the organs of these invertebrates—, where the dominant presence of V. pectenicida was detected in sick specimens compared to healthy ones.
Under controlled conditions, healthy stars they fell ill and died When exposed to untreated fluids from affected individuals; when that fluid was previously warmed, the animals did not develop the pathology, indicating a heat-sensitive biological agent.
The team managed to isolate and cultivate the bacteria from affected samples and inoculate it into healthy specimens, reproducing the syndrome; a set of tests that, for outside experts, easily exceeds the bar of experimental evidence.
Transmission and conditions that aggravate the problem
Tests show that the pathogen can spread by direct contact and through water, and is capable of persisting outside the host for short periods.
Several experts point out that marine heat waves and thermal anomalies could favor the proliferation of Vibrio, a genus that thrives in warmer waters and could see its dynamics accelerated by climate change.
Although the focus of the massive outbreak was in the Pacific of North America, similar episodes have been observed and the presence of related strains in Europe, with records in France—including scallop farms—and specific events on the coasts of Spain and England.
Effects on the ecosystem
The drastic decline of the sunflower starfish has triggered the hedgehog populations, their usual prey, causing massive consumption of kelp forests and disrupting key ecological functions.
In Northern California, the loss of up to 95% of kelp within a decade, affecting fish, otters and other species that use these forests as habitat and food sources.
Next steps and lines of action
With the pathogen identified, options such as breeding in captivity, the transfer of healthy populations to safe areas and the search for resistant variants to strengthen resilience.
Complementary strategies are explored, from probiotics to restoration programs that integrate sea urchin control and kelp recovery, in order to restabilize food webs.
Voices like that of Antonio Figueras ask prudence not to close the case: the history of the disease includes red herrings and environmental factors could intervene that modulate the severity of the outbreaks.
The current scenario strongly links the presence of Vibrio pectenicida with the outbreak, in a context marked by ocean heat and ecological imbalanceIdentifying the culprit allows for the implementation of solutions at scale, although their effectiveness will depend on the right combination of science, adaptive management, and ongoing monitoring.