Sea stars in Southern California are dying in droves from mysterious disease
A mysterious disease that has been killing massive numbers of sea stars along the West Coast is now firmly entrenched in Southern California waters.
“Other than perhaps some of the islands, where it hasn’t ravaged yet, it’s pretty clearly throughout Southern California at this point,” said Pete Raimondi, a researcher at the University of California Santa Cruz who has been leading efforts to track the disease's spread.
The illness, commonly referred to as "sea star wasting disease" targets several species of sea star, including most major ones found along the West Coast. Though its effects vary among species, it is often lethal, causing some species to disintegrate and liquify into bacterial goop within days.
Scientists do not yet know what is causing the widespread illness, which has been seen in populations stretching up into Alaska. A similar wasting disease seen in the 1980s was tied to warmer water temperatures caused by an El Niño weather system. That is most likely not the case in the current outbreak since an El Niño has not occurred in several years.
“We’re in unchartered waters in lots of ways. We’re in the middle of a disease the likes of which we haven’t seen before, meaning the spatial extent and the movement from north to south. It’s apparently unassociated with warming water, which other kind of events have typically been associated with," Raimondi said.
Difficult to diagnose
Ian Hewson first heard of sea star die-offs in the Pacific Ocean last summer, but he said he really started paying attention when public aquariums in Seattle and Vancouver began losing their sea stars.
"They’d been in captivity for 30 years, and they died in the space of about 24 hours. That’s when I sort of realized that there was something going on there, that there was potentially some form of waterborne pathogen or some other disease agent," Hewson said. "And that’s basically when I swung into action.”
Hewson is a microbial oceanographer at Cornell University and is part of a collaborative effort to determine the nature and extent of the disease. He said it's difficult to know whether the disease is caused by bacteria, a virus or another pathogen in the environment. Part of the problem is sea stars move seawater into and out of their bodies.
"That actually makes it more complicated to look from a microbial standpoint, because seawater has itself naturally about a million bacteria per [millileter] and about 10 million viruses per [millileter], and sorting out what’s naturally there [and] is not involved in the disease, with what is involved in the disease is somewhat of a challenge," Hewson said.
Hewson said he and other researchers are monitoring potential pathogens and are working to better understand their incubation periods.
"We’ve been doing that now for several weeks — in a couple cases, for a couple months — and it’s very difficult to say when we’ll have a definitive answer,” he said.
Last Saturday, Jayson Smith, a marine conservation ecologist at Cal Poly Pomona was at Crystal Cove State Park in Laguna Beach, along with other researchers and students from his school and California State University--Fullerton. They were performing a biannual count of marine organisms living in the intertidal zone.
Smith said that the last time they surveyed the spot, they tallied up 111 sea stars.
"We surveyed in the summer and fall and really didn’t see very many affected sea stars at all, you know, one percent, zero percent at most of the sites," Smith said. "We actually thought we were going to escape it. And then when January, early February came around, we just got hit really hard, and we’ve lost probably 95 percent of our sea stars."
At the end of the day on Saturday, Smith and the others had found 11 sea stars, four of which were exhibiting signs of infection. Despite that, he said the low numbers were actually a welcome sight.
"Clearly it’s not the high abundances that it used to be, but it is positive sign that there are some here, because that’s more than I’ve seen in other places," Smith said.
The next day, Smith and his crew found no sea stars at Shaws Cove, a spot where they had previously counted about 400.
Tiny silver linings
As bleak as the widespread die-offs have been, some researchers are excited by the research opportunity they bring. Sea stars are the dominant predators in many marine ecosystems, and Raimondi said that their absence will allow scientists to test predictions about their role in marine environments. It will also allow them to observe the ways in which sea stars return to their habitats.
"Will it be patchy everywhere? Will it sweep up and down the coast? Will there be a delay? All those kinds of things will give us a lot of information about how changes — either anthropogenic or natural disturbances — are likely to affect systems in the future," Raimondi said. "That will be really important information.”
Most of those effects will take years of careful observation to understand, but some new discoveries already seem to be exhibiting themselves. Raimondi said that he'd received reports this week that baby sea stars have been seen in some areas that have lost their adult sea stars to the wasting disease.
"It’s very exciting to see these new guys. We don’t know if it’s symptomatic or whether it’s isolated. But it’s better than not seeing them at all. That’s for sure," Raimondi said.
Raimondi said that such an appearance of baby sea stars is uncommon and that he and other scientists will try to understand what is causing it. His group already tracks reports from citizen scientists on instances of wasting disease that they find. He said he's hoping beach goers will begin contributing sightings of young sea stars.
"If people start seeing babies, then we would love to know about that,” Raimondi said.