Billions of sea stars have succumbed to a devastating illness known as sea star wasting disease, with their bodies disintegrating into a gelatinous mass. Recent research has pinpointed the specific pathogen responsible for this crisis: a bacterium called Vibrio pectenicida. This breakthrough follows four years of extensive gene sequencing and laboratory experiments, which finally identified the cause of this alarming epidemic.
The outbreak, first reported in November 2013, has had catastrophic effects on marine ecosystems along the West Coast of North America. It has also been observed in other regions globally, affecting more than 40 species of starfish. The disease manifests through lesions on the starfish’s exterior, leading to the breakdown of their muscles and the eventual loss of limbs. Within just a few days, affected starfish die.
Particularly hard hit were the sunflower sea stars (Pycnopodia helianthoides), which experienced a decline of over 90 percent in population. This species, notable for its vibrant orange and purple hues and up to 24 arms, has virtually vanished from coastlines stretching from Alaska to Mexico by 2015. Consequently, the International Union for Conservation of Nature classified them as critically endangered in 2020.
Beyond their aesthetic appeal, sea stars play a crucial role in marine ecosystems by controlling populations of sea urchins, which feed on kelp. The absence of these starfish has allowed sea urchins to proliferate, leading to the destruction of kelp forests that are vital habitats for numerous marine species, including sea otters, seals, and various fish and crustaceans. Kelp forests also serve as important carbon sinks, helping to mitigate climate change effects and protect shorelines.
The newly identified pathogen, Vibrio pectenicida, belongs to the same genus responsible for cholera in humans and coral bleaching. According to Drew Harvell, a marine ecologist at the University of Washington, this bacterium poses unique challenges for detection due to its ability to produce an immune-inhibiting toxin. Initial investigations mistakenly suggested that a virus was responsible, making the identification of a common bacterial pathogen a significant surprise for researchers.
The research team faced numerous challenges in isolating the bacterium, including the difficulty of locating healthy starfish for comparison and the lack of visible pathogens in diseased tissue. Led by evolutionary ecologist Melanie Prentice, the team conducted seven controlled experiments using healthy sunflower sea stars bred in captivity. When exposed to infected tissue, the starfish exhibited the same deteriorative symptoms, confirming the bacterium’s role in the disease.
Laboratory findings indicated that if the pathogen were viral, it would survive filtration and heat treatment. However, starfish exposed to treated materials remained healthy, confirming the disease’s bacterial origin. Subsequent RNA sequencing of infected samples identified V. pectenicida, specifically the FHCF-3 strain, as the responsible agent. The excitement among researchers was palpable; Alyssa Gehman, a marine disease ecologist from the University of British Columbia, described the moment of discovery, stating, “We all had chills. We thought, that’s it. We have it. That’s what causes wasting.”
Climate change may exacerbate the problem, as warmer waters are known to facilitate the growth of Vibrio bacteria. Some sunflower sea star populations have managed to survive in the cooler fjords of British Columbia, sparking hope that temperature could play a role in their recovery. Gehman noted, “Those patterns of Vibrio in general suggest that we really should look down that road to see how temperature dependence matters.”
Understanding the specific causes behind the decline of sunflower sea stars is vital for their conservation and the health of kelp forest ecosystems. As highlighted by Jono Wilson, director of ocean science for The Nature Conservancy in California, recovering this species is essential for restoring the balance within marine environments.
The research findings were published in the journal Nature Ecology & Evolution, providing a clearer understanding of the challenges facing marine life and the urgent need for conservation efforts. Protecting sea stars not only preserves their beauty but also safeguards the intricate ecosystems they support, ensuring that the oceans remain vibrant and resilient.
