People woke early to greet the low tide at Cannon Beach, Oregon, in late July. They wandered through sand to a pillar of stone at the edge of the Pacific called Haystack Rock. Some were looking up at birds, but most of us were looking down into the tide pools. We were saying hello to the invertebrates that cover boulders. And we were saying goodbye to the sea stars.

Sea stars have been dying of sea star wasting syndrome along the Pacific coast in large numbers during the past year. Recently the plague has made its way to Oregon. At Haystack Rock, the stars started dying in June - first the larger sunflower stars, then the ochre sea stars.

A group of volunteer naturalists called the Friends of Haystack Rock was on hand to field questions. One volunteer pointed out a sick sea star. It had a white spot on one of its arms but otherwise looked fine to the untrained eye. “That one will be dead in a week,” she said sadly. A visitor asked her why this was happening. We don’t know, she responded.

She is right that there is a lot that we don’t know about this specific event. However there is also a lot we do know about what causes sea star die-off in general.

The afflicted sea stars disintegrate after getting one or more white spots, lesions that mark the early stage of the syndrome. As the lesions grow, arms break off the body and the rigid plates of the star’s skeleton turn to mush. This is most likely due to a virus or bacteria according to epidemiological studies. We also know that the seawater has been warmer than usual and that pathogens tend to thrive in warmer water.

Sea star wasting syndrome has struck before on the West Coast – during El Niño events when ocean temperatures are warmer than usual in the eastern Pacific. This time around, the pattern of sea star die-offs hasn’t been like it was during previous El Niño events. Sea stars are turning to mush at a much higher rate.

El Niño isn’t following the pattern this year that it has in the past either. During a typical El Niño, weaker upwelling off the coast of South America leads to a tongue of warm water stretching across the surface of the tropical Pacific. This was projected to occur this year. But there has been unusually warm water throughout the Pacific this year. Scientists at NOAA speculate that El Niño has not kicked in yet because the atmospheric side of El Niño relies on a temperature gradient across the Pacific, which we are not seeing, at least not yet. (See NOAA’s ENSO Blog for the latest El Niño updates.)

Despite the lack of El Niño, the water in the northeast Pacific has been warmer than usual for months, which can have an impact on sea stars and disease. We know that outbreaks of marine disease coincide with unusually warm sea surface temperatures. Although climate influences on marine diseases are still not well understood, we do know that warmer ocean waters can cause pathogens to change – to increase in activity and their ability to cause disease - according to an article that Cornell University marine biologist Colleen Burge and colleagues published this year. Additionally, warmer water may make sea stars more susceptible to disease.

Climate change plays some role in the warm Pacific waters just like it plays some role in everything, but it can be difficult to know exactly how it is pulling the strings. We do know that this June was the warmest June on record with the highest average land and ocean temperatures. Additionally, there has been a patch of unusually warm surface ocean water in the northeast Pacific near the sea stars for months. However, this sea star die-off started a year ago, when the northeast Pacific was not abnormally warm. Temperature may be a contributing factor, but it is not the only factor.

Along with climate change, we humans affect marine ecosystems in many other ways too, from overfishing to inadvertently moving species around the planet.

Last winter when news media speculated about a connection between the Fukushima nuclear disaster and the sea star die-off, researchers at UC Santa Cruz, who have been monitoring Pacific tide pools for decades, posted on their Sea Star Wasting Syndrome Updates page that, “there has been substantial speculation in the media that the disease could be a result of increased radiation from the nuclear power plant disaster in Fukushima, Japan. We have no evidence to suggest that radiation is a likely culprit.”

Smithsonian sea star expert Chris Mah (@echinoblog) went into more detail about the lack of connection between the Fukushima nuclear disaster and the sea star die-off in a post at Deep Sea News. He explained that sea star wasting syndrome predates the nuclear disaster, that sea star wasting is found in the Atlantic as well, and that no other life in the tide pools appears to be affected besides the stars.

Sea stars and other echinoderms are known for population booms and busts and they are susceptible to pathogens. This die-off is bigger than we’ve seen in the past, affecting more species and more individuals in more areas. However, the sea stars’ boom and bust lifestyle might be a key to their survival. A massive die-off followed by slow recovery is a pattern that scientists have seen before. In this case, researchers are hopeful recovery will happen.

Watching for signs of recovery, UC Santa Cruz is documenting the locations of baby sea stars along the coast. They have recently seen evidence of new baby sea stars in a few areas that have been severely affected by the wasting syndrome. Getting citizen scientists involved, they have set up an online Juvenile Sea Star Observation Log on their website so that the public can report sightings, too.

Perhaps the next generation can make it through this calamity. Perhaps they can reproduce fast enough to counter this plague. In the meantime, researchers are working to learn more about why this episode of sea star wasting syndrome has been so severe.