Scientists have identified the killer of five billion sea stars

Sea stars. Photo: Tahsin Ceylan / Anadolu via Getty Images

Sea stars are amazing creatures, usually having five arms, though species with significantly more arms are found. The color palette of these animals ranges from vibrant orange to complex patterns of purple, brown, and green hues. Typically, these marine animals live 20 or more years.

However, since 2013, sea star populations along the Pacific coast of North America — from Mexico to Alaska — have begun to rapidly decline due to a mysterious disease. The epidemic has affected more than twenty species, and this process continues to this day.

One of the largest sea star species in the world, Pycnopodia helianthoides, or the sunflower sea star, was most severely affected. Its maximum arm span (their number ranges from 16 to 24) can reach 1 meter. In the first five years of the outbreak, their population declined by 90%.

As researchers note, the progression of the disease looks horrific. In a healthy sea star, the arms are usually lush and evenly spread out. But during the disease, lesions and ulcers appear on its body, after which the limbs literally fall off.

For a long time, the cause of this remained unknown, and it took scientists more than ten years to find the culprit, going through many erroneous theories and unexpected turns in the research.

Павялічыць

Pycnopodia helianthoides, or sunflower sea star. Photo: Wikimedia Commons

Early work hinted that a densovirus might be the cause. However, it was later revealed that it is a common inhabitant of healthy sea stars and is not associated with the disease.

Other attempts to find the killer were unsuccessful. As the authors explain, the reason was that researchers studied tissue samples from already deceased animals, which lacked an important biological fluid surrounding the internal organs.

Only during the latest study was a detailed analysis of this fluid conducted. It was there that bacteria named Vibrio pectenicida were discovered. Interestingly, these same bacteria also infect mollusks.

As scientists note, tracking the source of ecological diseases, especially underwater, is extremely difficult, which is why such work resembles a real detective investigation.

What's next?

Now that the cause of the disease is known, scientists have a much better chance to intervene and help sea stars. Researchers believe they can test surviving individuals for health and consider the possibility of relocating them.

The possibility of breeding sea stars in captivity for their subsequent reintroduction into areas where they have practically disappeared is also being discussed. In addition, specialists plan to check whether some populations have natural immunity, and whether methods such as the use of probiotics can help strengthen their defense against the disease.

According to researchers, restoring sea star populations is important for the entire Pacific ecosystem. Despite their harmless appearance, they are voracious predators that control the number of sea urchins and eat almost everything that lives on the seabed. When sea stars became significantly fewer, the urchin population exploded and, over ten years, destroyed about 95% of kelp forests in Northern California.

These underwater kelp forests are vital because they provide food and habitat for many animals, including fish, sea otters, and seals. Scientists hope that new discoveries will allow them to restore sea star populations and thereby bring valuable underwater ecosystems back to life.

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