Billions of sea stars have succumbed to a severe illness known as sea star wasting disease, which has devastated populations along the coastlines of North America and beyond. Recent groundbreaking research has pinpointed the exact cause of this widespread epidemic: a bacterium identified as Vibrio pectenicida. This discovery follows four years of extensive gene sequencing and laboratory experiments, shedding light on a crisis that has been alarming ecologists since it first appeared in November 2013.
The outbreak of sea star wasting disease has significantly impacted marine ecosystems, affecting over 40 species globally. The disease manifests with visible lesions on the starfish’s exterior, leading to rapid deterioration. Muscles disintegrate, arms twist, and within days, the organism is dead. Notably, the sunflower sea star (Pycnopodia helianthoides) has faced catastrophic losses, with populations declining by more than 90 percent. Once vibrant with orange and purple hues and boasting up to 24 arms, these sea stars have largely disappeared from the West Coast, prompting the International Union for Conservation of Nature (IUCN) to classify them as critically endangered in 2020.
The ecological ramifications of this decline are profound. Sea stars play a crucial role in their habitats by preying on sea urchins, which, in the absence of natural predators, have proliferated unchecked. This unchecked growth has led to the degradation of kelp forests, transforming these once-thriving underwater ecosystems into barren landscapes. Kelp forests are vital as they support numerous species, including sea otters, seals, and various commercially important fish. They also act as significant carbon sinks, helping mitigate climate change effects.
The research team, led by Melanie Prentice, conducted controlled exposure experiments using sunflower sea stars bred in captivity. The team sought to determine whether the pathogen was viral or bacterial. Initial assumptions pointed towards a viral cause due to the lack of visible pathogens in infected tissues. However, when healthy starfish exposed to filtered or heated diseased material survived, it indicated the bacterial nature of the illness.
Through RNA sequencing of samples from both laboratory and natural environments, the team identified V. pectenicida, a known pathogen affecting marine species like scallop larvae and oysters. The specific strain responsible for the current outbreak was subsequently isolated and used to infect healthy starfish, confirming its role in the disease’s progression. Alyssa Gehman, a marine disease ecologist from the University of British Columbia and the Hakai Institute, described the moment of discovery: “We all had chills. We thought, that’s it. We have it. That’s what causes wasting.”
Climate change is suspected to exacerbate the situation, as warmer waters are known to facilitate the growth of Vibrio bacteria. Some sunflower sea star populations in the colder waters of British Columbia have shown resilience, suggesting that temperature may play a critical role in the bacteria’s proliferation. Gehman emphasized the importance of understanding these patterns, stating, “We really should look down that road to see how temperature dependence matters.”
This research, published in Nature Ecology & Evolution, marks a significant step toward understanding and potentially mitigating the impacts of sea star wasting disease. As scientists continue to unravel the complexities of marine infectious diseases, the hope is to protect these vital species and, by extension, the ecosystems they support. The loss of sea stars would not only diminish the beauty of our oceans but also threaten the ecological balance that various marine life, including humans, relies on.
