Mass Sea Star Death Leaves Researchers Perplexed

73

All along the Pacific coast, from Southern California to British Columbia, sea stars are mysteriously dying.

Marine ecologists at UC Santa Cruz tracked this epidemic all along the West Coast, looking specifically at the rocky intertidal, said Long Marine Lab research specialist Melissa Redfield.

This inexplicable phenomenon, known as Sea Star Wasting Syndrome, begins with slight discoloration and small lesions on the sea star’s body that quickly become lethal. Though normally sea stars can grow new limbs just as a lizard does with its tail, in these cases the wounds don’t heal. In a matter of days, the sea stars disintegrate into goo.

“The wasting is a series of symptoms and it differs by species, but when they get this illness, it quickly affects the tissue. It then expands on the entire species so they either disintegrate or begin dismembering — their arms fall off or walk away,” said ecology and evolutionary biology department chair Pete Raimondi.

First noticed in a tide pool in Washington state last summer, the spread of the illness has been rapid and unprecedented.

“The spread of this disease has been really patchy — we’re still trying to figure out what’s going on,” Redfield said. “We didn’t start seeing it in the Santa Cruz area until early September, and just last month we started to notice Santa Barbara and other parts of Southern California are now getting hit pretty hard.”

Scientists are unsure of the underlying cause at this point, but speculate it has to do with either a pathogen or bacteria, ocean acidification, warm water conditions, radiation leakage or any combination of these things.

“The driver of it — we don’t know. We also don’t know if the pathogen is exotic or native. If it’s native then why has it been so devastating recently? If it’s exotic, where did it come from?” Raimondi said. “We need to figure out where it came from, how it got here, whether it was natural or by a cargo vessel, hitchhiking on some other animal or a current shift related to climate change. There’s a lot of work we still need to do.”

Other work is also being done at Western Washington University with Benjamin Miner, associate professor of biology. Miner is among a group of scientists striving to uncover the mysteries of the syndrome.

Miner’s lab is currently working on several laboratory experiments in which his team observes tanks filled with selected healthy and unhealthy sea stars, tests them with a variety of controlled variables and monitors their health in order to track how the illness spreads.

There are also researchers doing pathology work and looking carefully at the cells to see if there are foreign organisms involved. Others are doing genomics work, including DNA sequencing to look at viruses and bacteria, Miner said.

“Even if we figure out what it is, no one is likely to propose ways to intervene in any rapid manner,” Miner said. “That being said, I would be surprised if we lose all the stars along the coast.”

Similar occurrences of mass sea star wasting have been observed in relation to the storm known as El Niño, Raimondi said. However, during this previous occurrence of mass sea star death, researchers were able to associate the deaths with the warmer water, which is not the case now.

“The root cause of this is a pathogen, but we don’t know what that is exactly. It could either be a bacteria, virus or parasite causing them to be compromised,” Raimondi said. “There has been a lot of research done suggesting this pathogen can be transmitted [by affected sea stars].”

Because sea stars are keystone predators, and many things don’t prey on them, they could have a large impact on their ecosystems if they disappear, Redfield said. Sea stars eat mollusks, clams, oysters and mussels, which could begin to overrun their habitats if sea stars are removed.

“[The sea star’s ecosystem] could look very different from what we see now,” Raimondi said.

However, there have been cases of sea stars regrowing arms and healing lesions. Although many sea stars have died, there is hope that the sea stars are not necessarily going to die once they get the disease, Redfield said.

“We really don’t know if we’re in the beginning, middle or end of this trend,” Raimondi said.

There are approximately 10 to 12 sea star species being affected, but so far the illness has not been seen in any other species, Raimondi said. It has been difficult to understand how many sea stars are dying since there wasn’t much of a baseline to begin with. In areas like Washington, where the illness was first seen, the effects are detrimental to the population of sea stars.

“[In Puget Sound] there are almost none left compared to how many there were previously,” Miner said. “You might find a few individuals here and there, but for the most part, where there were once hundreds or thousands, there aren’t any now.”

For those who want to help out or learn more,
visit http://seastarwasting.org.