Washington: Starfish have been mysteriously dying by the millions in recent months along the US west coast, worrying biologists who say the sea creatures are key to the marine ecosystem.
Scientists first started noticing the mass deaths in June 2013. Different types of starfish, also known as sea stars, were affected, from wild ones along the coast to those in captivity, according to Jonathan Sleeman, director of the US Geological Survey’s National Wildlife Health Center.
Contaminated water that has been leaking from Fukishima for years is just now reaching the west coast, but they do say there are also deaths on the east coast. According to one site, “Marine invertebrates, such as bottom-dwelling starfish and sea urchins, are particularly proficient at absorbing a wide range of ingested radioisotopes” Other theories: methane increase, virus or other pathogen that is thriving in the ocean temperature change.
It’s a sea mystery that has stumped scientists along the West Coast for years.
But a group of Cal State Fullerton students and marine biologists are on the hunt for answers about a mysterious epidemic that wiped out millions of sea stars in recent years. …
From 2013 through 2015, sea star wasting disease hit the West Coast from British Columbia to Mexico, melting once-healthy sea stars into globs of goo. It was the largest known die-off of the species.
According to the University of Santa Cruz, which has been tracking the wasting syndrome since it first hit the West Coast, it’s not the first time the the disease has hit. There were similar die-offs in the 1970s, ’80s and ’90s, but not of the magnitude seen in recent years. …
“Sea stars can go from seemingly healthy to dead in a few days, and during the course of the sickness, the tissue seems to dissolve,” said Jennifer L. Burnaford, associate professor of biological science at Cal State Fullerton. … The data showed that incidences of the disease were “not uniform across the affected area with proportionally greater population declines in the southern regions,” according to the study.
… The study didn’t find proof that elevated seawater temperatures or high-density population of starfish, earlier thought to be factors, were responsible for the spread of sea star wasting disease.
It seems very strange to me that they did not yet identify any foreign substances or cellular differences in the dead vs healthy sea stars. Ah, this seems promising:
Starfish wasting disease was first identified in 1979, but since then, no one has been able to pin down a precise cause, according to Pete Raimondi, a professor of ecology and evolutionary biology at UC Santa Cruz and co-author of the new sea star study. Scientists long believed that outbreaks of the disease — which occurred in 1983, 1998 and most recently starting in 2013 — may be linked to environmental stressors, such as spikes in ocean temperature or pollution from shipping lanes and marinas, Raimondi told Live Science.
But while such stressors may have something to do with the rapid spread of sea star wasting syndrome, the researchers now think the underlying cause of the disease is the waterborne densovirus.
“What convinced me that this was an infectious agent was that sea stars that had been in captivity in public aquariums for 30 years suddenly died,” said Ian Hewson, an associate professor of microbiology at Cornell and lead author of the study. “There was good evidence that it was something coming in through the intake for the aquariums that wasn’t being removed by the sand filtration. And [aquariums] receiving UV-treated water weren’t getting sick.”
To test this hypothesis, Hewson and his team used a process known as metagenomics, in which genetic material is collected directly from environmental samples and then sequenced in a lab. The researchers collected tissue samples from both healthy starfish and those affected by the wasting disease. They then extracted DNA from these samples and tried to figure out how the healthy tissue differed from the infected tissue. The difference between the two kinds of samples soon became clear: the infected tissue contained a densovirus, Hewson said. [5 Mysterious Animal Die-Offs]
“Armed with that knowledge, we went out and tried to understand whether the association between the disease and the densovirus was robust,” Hewson told Live Science. Aided by Raimondi and other scientists on the West Coast, the researchers collected 465 healthy and diseased sea stars, he added.
With sea stars in hand, the researchers determined which of the animals were infected with the virus. They then measured how much of the virus was present in the animal’s tissue per unit of weight— a measurement known as viral load. Ultimately, they found a significant association between the presence of the disease and the abundance of the viral tissue, according to Hewson. The researchers believe this association supports their hypothesis that the wasting disease is caused by the sea-star associated densovirus.
In addition to these tests, the researchers infected some healthy sea stars with the densovirus, and the animals became sick within 7 to 10 days, Hewson said.
“What we’re dealing with are animals that are crawling with bacteria and other microorganisms. Trying to prove beyond a reasonable doubt that any specific virus is responsible for the disease is a really big challenge because you can’t isolate it away from those native bacteria. But our evidence is very strong that it’s a sea star associated densovirus,” Hewson said …
The culprit may be a virus that attacks sea stars. Here is a paper on PNAS on the topic.
Sea stars inhabiting the Northeast Pacific Coast have recently experienced an extensive outbreak of wasting disease, leading to their degradation and disappearance from many coastal areas. In this paper, we present evidence that the cause of the disease is transmissible from disease-affected animals to apparently healthy individuals, that the disease-causing agent is a virus-sized microorganism, and that the best candidate viral taxon, the sea star-associated densovirus (SSaDV), is in greater abundance in diseased than in healthy sea stars.