Billions of sea stars have succumbed to a devastating illness known as sea star wasting disease, which has been responsible for their rapid decline since its emergence. Recent research has pinpointed the specific pathogen responsible for this epidemic as Vibrio pectenicida, a bacterium that has eluded identification until now. This breakthrough follows four years of genome sequencing and laboratory experiments.
The outbreak, first reported in November 2013, has severely impacted marine ecosystems along the west coast of North America. More than 40 species worldwide have been affected, with some regions witnessing dramatic declines. The sunflower sea star (Pycnopodia helianthoides), in particular, has suffered a staggering 90 percent decrease in population. Once thriving in vibrant hues of orange and purple, these sea stars have nearly vanished from coastal waters stretching from Alaska to Mexico.
Understanding the Disease and Its Impact
The disease manifests through lesions on the sea stars’ bodies, leading to muscle disintegration, twisted arms, and ultimately death within days. The decline of sunflower sea stars has created a cascading effect on marine ecosystems, particularly affecting kelp forests. Without these predators to control sea urchin populations, urchins have proliferated, resulting in the destruction of kelp habitats that are vital for numerous marine species.
Kelp forests play a crucial role in ocean health, providing habitat for species such as sea otters, seals, and various fish. They also contribute to carbon dioxide absorption, mitigating greenhouse gas emissions and protecting coastlines from severe weather effects. The link between the loss of sea stars and the deterioration of these ecosystems highlights the urgency of finding a solution to the disease.
Researchers have established that Vibrio pectenicida belongs to the same bacterial genus responsible for cholera in humans and coral bleaching. According to Drew Harvell, a marine ecologist at the University of Washington, the bacterium’s ability to evade detection is attributed to its production of an immune-inhibiting toxin. Initial assumptions suggested a viral cause for the disease, making the identification of a bacterial pathogen surprising.
Research Breakthroughs and Future Implications
Challenges in identifying the bacterium included the difficulty of finding disease-free starfish for comparison and the limited knowledge of marine infectious diseases. Melanie Prentice, an evolutionary ecologist, led a series of controlled exposure experiments using sunflower sea stars bred in captivity. Healthy starfish exposed to infected tissue exhibited the characteristic deterioration of limbs, confirming the bacterial origin of the disease.
RNA sequencing of samples from both laboratory and natural environments revealed the presence of V. pectenicida, specifically a strain known as FHCF-3. This strain was isolated from infected sea stars and subsequently used to infect healthy specimens, leading to observable symptoms of the disease. Alyssa Gehman, a marine disease ecologist from the University of British Columbia, described the moment of discovery as a chilling confirmation of their findings.
Understanding the mechanisms behind the sunflower sea star’s decline is essential for conservation efforts. Jono Wilson, director of ocean science for The Nature Conservancy‘s California chapter, emphasized that recovering this species could restore the health of kelp forest ecosystems.
Researchers suspect that climate change may exacerbate the outbreak, as Vibrio bacteria thrive in warmer waters. Some sunflower sea star populations persist in the cooler waters of British Columbia, where the bacteria may be less viable. This connection underscores the importance of addressing climate factors to protect marine biodiversity.
As scientists continue to investigate the implications of Vibrio pectenicida, there is hope that understanding this disease could lead to effective conservation strategies. The vibrant marine environments that rely on the presence of sea stars are at stake, and their survival is critical for maintaining ecological balance.
This research was published in Nature Ecology & Evolution, marking a significant step forward in marine disease research and conservation efforts. The future of sea stars and the ecosystems they support depends on continued investigation and proactive measures.
