After years of research, scientists have finally uncovered the cause of a mysterious disease that decimated more than 5 billion sea stars, also known as starfish, along the Pacific coast of North America.
Since 2013, a phenomenon known as sea star wasting disease has led to mass die-offs from Mexico to Alaska, impacting over 20 species, with the sunflower sea star being the hardest hit.
This particular species has lost approximately 90% of its population in the first five years of the outbreak.
Describing the disease, marine disease ecologist Alyssa Gehman from the Hakai Institute in British Columbia remarked, “It’s really quite gruesome.”
Healthy sea stars typically exhibit “puffy arms sticking straight out,” while the wasting disease prompts the growth of lesions, leading to the alarming loss of limbs.
The cause behind this catastrophic event has been identified as a bacterium that has also affected shellfish, according to a newly published study in the journal Nature Ecology and Evolution.
Rebecca Vega Thurber, a marine microbiologist at the University of California, Santa Barbara, and not part of the study, emphasized the significance of the findings, stating, “This solves a long-standing question about a very serious disease in the ocean.”
Sea stars usually have five arms, with some species boasting up to 24, and they display an array of colors, varying from solid orange to intricate patterns of orange, purple, brown, and green.
The National Park Service outlines symptoms of the sea star wasting syndrome, which include twisted arms, white lesions, deflation of limbs and body, loss of arms, and overall body disintegration, with death occurring over a matter of days or weeks.
The search for the disease’s cause spanned more than a decade, filled with numerous false leads and complexities.
Initially, some studies suspected that a virus might be the culprit, but early investigations centered around densovirus revealed it to be a normal inhabitant of healthy sea stars, unrelated to the disease.
Melanie Prentice, a co-author of the new study at the Hakai Institute, highlighted how other research efforts failed to identify the true cause by examining tissue samples from deceased sea stars that lacked the surrounding bodily fluid essential for diagnosis.
The recent study made a breakthrough by analyzing the coelomic fluid, which surrounds the organs of sea stars, revealing the presence of Vibrio pectenicida bacteria.
Blake Ushijima, a microbiologist at the University of North Carolina, Wilmington, praised the research team’s effort, saying, “It’s incredibly difficult to trace the source of so many environmental diseases, especially underwater.”
Understanding the cause of the sea star wasting disease opens up avenues for intervention, especially for the critically endangered sunflower sea star.
Prentice noted that with the newfound knowledge, scientists can potentially assess which sea star populations are still healthy and consider relocating or breeding these specimens in captivity for future reintroduction into affected areas.
The study also underscores the crucial role of Vibrio bacteria as indicators of climate change, with their prevalence increasing in warmer sea temperatures.
Future research will focus on examining the link between rising seawater temperatures and the sea star wasting disease to help develop better remediation methods.
The scientific community aims to investigate if specific sea star populations possess natural immunity and whether treatments like probiotics might enhance the immune responses to the disease.
The recovery of sea stars is vital not only for their species but also for the entire Pacific ecosystem, as healthy sea stars play a critical role in controlling sea urchin populations.
Gehman explains, “Sunflower sea stars look sort of innocent when you see them, but they eat almost everything that lives on the bottom of the ocean.”
With the drastic decrease in sea star numbers, sea urchin populations have surged, leading to the overconsumption of kelp forests in Northern California, which have declined by approximately 95% within a decade.
These kelp forests are essential habitats for various marine animals, including fish, sea otters, and seals.
Researchers are optimistic that the new findings will enable efforts to restore sea star populations, subsequently aiding in the regeneration of the critical kelp forests that can be likened to the “rainforests of the ocean,” as described by Thurber.
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