In 2013, divers began to notice something terrible happening to sea stars in the waters around Washington State. The sea stars were disintegrating and dying. Over 20 species were impacted, and it's estimated that about 5 billion of the creatures died.
Scientists began to investigate this phenomenon, which was linked to climate change. Now, a culprit has been found: a bacterium called Vibrio pectenicida strain FHCF-3, a distant relative of the pathogenic bacterium that causes cholera. This microbe is especially harmful to sunflower sea stars, which have fared the worst. The findings have been reported in Nature Ecology & Evolution.
While the most serious effects and die-offs subsided around 2014, this problematic microbe now has seasonal effects on marine life. Sea star wasting is now documented around the world, and happens mostly in warmer months.
Since so many sea stars were killed, that allowed their primary food source of sea urchins to flourish. There has been an ecological domino effect, and the sea urchin boom has led to the decimation of kelp forests that the urchins consume.
In this study, the researchers identified the pathogen by exposing sea stars to filtered tissue from sick animals. But the unaffected animals did not fall ill. They tried exposing healthy sea stars to body fluid from sick sea stars, and then the sickness was transmitted.
After that, the researchers used genetic tools to identify everything in the body fluids, which revealed the high levels of DNA from the Vibrio pectenicida strain FHCF-3 pathogen. This effort showed that Vibrio pectenicida, which has been found in several oceans, was likely to blame for the mass die-off.
This bacterium is difficult to grow in the lab, but the researchers found the right conditions, and were able to do more testing. This work showed that higher doses of the bacterium made sea stars more sick, and that sea stars exposed to inactivated bacteria did not get sick.
Now, the researchers want to confirm that this microbe is also causing wasting in other sea star species.
Other scientists are working on raising more sea stars in captivity in the hopes that they can be released to rebuild wild populations. If some of these captive raised sea stars have developed resistance to the pathogen, the scientists also want to focus on expanding those populations.
Sources: Science, Nature Ecology & Evolution
