A significant crisis is unfolding in marine ecosystems as billions of sea stars have succumbed to a devastating illness known as sea star wasting disease. Researchers have identified the pathogen responsible for this epidemic: a bacterium called Vibrio pectenicida. This breakthrough comes after four years of extensive gene sequencing and laboratory experiments aimed at understanding the origins of this crisis, which first emerged in November 2013 along the west coast of North America.
The outbreak has led to alarming declines in sea star populations, with reports indicating that more than 40 species worldwide have been affected. The disease manifests with lesions on the starfish’s exterior, leading to disintegration of muscle tissue and causing the arms to twist and fall off. Within days, the affected sea stars are dead.
The sunflower sea star (*Pycnopodia helianthoides*), characterized by its vibrant colors and numerous arms, has been particularly hard hit. Populations of this species have plummeted by over 90 percent in recent years. By 2015, these iconic marine creatures had almost disappeared from the coasts stretching from Alaska to Mexico. Their decline prompted the International Union for Conservation of Nature to classify them as critically endangered in 2020.
Sea stars play a crucial role in their ecosystems, primarily by preying on sea urchins. In their absence, sea urchin populations have surged, leading to the devastation of kelp forests, which are vital habitats for various marine species, including sea otters and fish. These underwater forests also serve as significant carbon sinks, helping to mitigate greenhouse gas concentrations and protect coastlines from storm damage.
The identification of Vibrio pectenicida marks a significant advancement in understanding this marine crisis. According to Drew Harvell, a marine ecologist at the University of Washington, the bacterium is part of a genus that also causes cholera in humans. Harvell noted that the challenge in identifying the pathogen stemmed from its atypical behavior, which did not conform to the characteristics of other bacteria commonly observed in diseased tissues.
The research team, which included scientists from various institutions, conducted seven controlled exposure experiments using sunflower sea stars bred in captivity. Healthy specimens exposed to infected tissues displayed the familiar symptoms of the disease, confirming the bacterial origin of the illness. As Alyssa Gehman, a marine disease ecologist at the Hakai Institute in Canada, remarked, “We all had chills. We thought, that’s it. We have it. That’s what causes wasting.”
This discovery arrives amidst growing concerns about the impact of climate change, which many researchers believe may be exacerbating the outbreak. Warmer waters are known to facilitate the proliferation of Vibrio bacteria. Interestingly, some sunflower sea star populations continue to survive in the colder waters of British Columbia, suggesting that temperature may play a critical role in the bacterium’s ability to thrive.
Understanding the dynamics between climate conditions and pathogen behavior is now seen as essential for the conservation of sea stars and the ecosystems they support. As Jono Wilson, the director of ocean science for The Nature Conservancy in California, stated, “Understanding what led to the loss of the sunflower sea star is a key step in recovering this species and all the benefits that kelp forest ecosystems provide.”
The findings of this research were published in the journal Nature Ecology & Evolution, offering a comprehensive overview of the pathogen responsible for the alarming decline in sea star populations. This knowledge not only aids in the quest to protect these marine creatures but also illuminates the broader environmental challenges posed by climate change and its effects on ocean health. The urgency for action has never been clearer, as the survival of sea stars is intricately linked to the health of marine ecosystems that humans rely on as well.
