The worst of the sea star wasting disease epidemic that decimated sea star populations along the West Coast during the past 19 months appears to be over at Haystack Rock — at least for now.
Most of what’s left are the juvenile sea stars that somehow survived the pathogenic onslaught that killed off more than 90 percent of their fellows during the 2014 beach season, according to Haystack Rock Awareness Coordinator Samantha Ferber, who recorded the death toll at three sites.
“Now that we’re past the peak of the disease, we’re starting to see that, across the board, sea stars don’t have as severe symptoms,” Ferber said. However, this may be because the sea stars that did show the most severe symptoms have all died out, she noted.
A fall survey that Ferber conducted with HRAP volunteers at and around Haystack Rock found that younger, smaller sea stars tended to fare better than older, larger ones.
• Of nine recorded ochre sea stars on Haystack Rock’s south wall, the only three that showed wasting signs had a radius (measured from the middle of their body to the tip of their longest limb) larger than 40 millimeters.
• Of 21 recorded ochre sea stars on the east boulder at the Needles, 14 showed wasting signs; the three sea stars with a radius smaller than 40 millimeters showed no signs. (While these numbers demonstrate that not all larger sea stars became infected, they add evidence to the claim that the smaller ones tended not to become infected.)
• Of 24 recorded ochre sea stars on the north boulders, the only five that showed wasting signs were larger than 40 millimeters.
Though Ferber and her team looked at all of the sea star species at Haystack Rock, they were only able to find ochres and six-rayed sea stars. Since the disease hit the rock last spring, “we have not seen a single sunflower (sea star),” a species that used to be seen in the tide pools during lower tides, she said.
On Jan. 20, HRAP will conduct another survey, which rates the disease status of individual specimens (with “1” meaning mild and “4” meaning severe). Ferber sends the results of these quarterly surveys to MARINe (Multi-Agency Rocky Intertidal Network), a consortium of universities and government agencies that monitors the ecology of rocky intertidal areas along the West Coast.
Before the wasting disease arrived in Cannon Beach last spring, it had already wiped out millions of sea stars at several sites along the West Coast, from Alaska to Southern California.
Wasting events have happened before, but “we’ve never seen the disease arrive at the levels that we’ve seen over the past year, year and a half,” said Melissa Miner, a research associate at the University of California, Santa Cruz, who works with MARINe.
The disease begins as lesions on a sea star’s body that degrade its tissue, shrivel up its rays and finally dissolve the invertebrate into a pale goo. It usually kills the organism within a few days to a couple of weeks, though some sea stars may slough off infected rays before the lesions reach their vital organs and later regenerate them.
Ferber first noticed the disease at Haystack Rock last March. By the end of July, most of the sea stars in the rock’s intertidal zone had died.
“Sea stars were falling apart,” she said. “We could see that sea stars were dying right in front of us.”
However, “that’s not happening anymore,” she said. “In general, we’re not seeing category 4 anymore. We’re seeing mostly category 1 or 2.”
Right now, HRAP and MARINe are focusing on the number of new sea stars in a given sea star population and what species are thriving in the aftermath of the wasting.
In recent months, six-rayed sea stars have proliferated at the Needles near Haystack Rock, despite that very few were recorded during HRAP’s July survey.
“I’ve never seen so many six-rayed sea stars in my life,” Ferber said, adding that “none of the six-rayed that we have found had any signs of disease.”
Because most of the larger sea stars that eat the smaller six-rayed species died of wasting disease, Ferber suspects that six-rayed sea stars don’t have many natural predators. “That’s just a hypothesis,” she said.
When HRAP conducts its sea star survey this month, she will be interested to see whether the six-rayed sea stars have continued to multiply.
Miner noted that at several coastal sites in Whatcom County, Wash., species of ochres and evasterias seem to be making a comeback.
“There are a lot of juveniles at nearly all of our sites, way more than we’ve ever seen before,” she said.
Last summer, marine scientists may have identified the virus responsible for the sea stars’ dramatic die back.
A disease-causing “densovirus” associated with sea stars that is “in greater abundance in diseased than in healthy sea stars” is “the most promising candidate disease agent” responsible for the mass mortality of sea stars, according to a study published in November in the journal Proceedings of the National Academy of Sciences.
However, that answer isn’t definitive. There are many unknowns, including the reason juvenile sea stars are less likely to contract and die from the wasting disease. Is it that larger sea stars carry a greater viral load of the densovirus (which naturally occurs in sea star populations)? Or is it just easier for younger sea stars to fight off illness?
“Because scientists don’t know what causes the densovirus to kill the sea stars — and what caused this outbreak to happen — it’s kind of hard to say for sure why the smaller individuals aren’t affected as much,” Ferber said.
And, since the virus was already present, the question remains: Why is the disease suddenly erupting on a much larger scale now than at any time in the past?
“We just don’t know at this point,” Miner said, adding that some environmental factors may have exacerbated the widespread wasting. “There’s still a lot to learn.”