Young starfish are staging a comeback in Oregon and Northern California, after a virus that melts the animal devastated adult populations along the northern West Coast starting in 2013.
"The number of juveniles was off the charts — higher than we'd ever seen — as much as 300 times normal," said Bruce Menge, an Oregon State University marine biologist and the study's lead author, in a statement the university released Wednesday. "It wasn't a case of high settlement, or more sea stars being born. They just had an extraordinary survival rate into the juvenile stage."
Menge and the rest of the team attribute the population spike to an unusual "smörgåsbord" of food available because of the absence of adult sea stars who compete with juveniles for the larval and juvenile mussels and barnacles they feed on. The adult population decreased by as much as 84 percent there, according to the statement.
Scientists are now scrambling to determine why the virus — found in sea stars as far back as 70 years ago — has turned into an epidemic before the "wasting disease" attacks this new generation of purple sea stars, as it continues to kill the adults along the West Coast.
Sea star recovery isn't a question of "will or won't [it] happen," but rather when and how long, Peter Raimondi, a University of California, Santa Cruz ecologist and evolutionary biologist, told PBS NewsHour. But some researchers worry that the juvenile invertebrates could still develop the illness as adults.
"We're kind of just waiting to see as we move into late spring and early summer of this year whether we have fresh outbreaks."
Raimondi co-authored a 2014 study that identified a densovirus as the cause of the disease that melts sea stars until they are just slime and calcium carbonate.
Starting in 2013, the disease killed millions of sea stars from Mexico to southern Alaska, in some regions, destroying as much as 95 percent of some populations. Although minor outbreaks of the disease had previously been recorded, the current epidemic is considered one of the most devastating marine ecosystem epidemics ever, according to an Oregon State University study published Wednesday that revealed the population of larval sea stars along the Oregon coast have increased.
Juvenile sea star populations in both Trinidad, California, and Santa Cruz, California, were also found to have increased, although not as much as in Oregon. Yet, scientists up and down the Pacific Coast aren't resting on these laurels. They are in a dash to determine why the virus is killing this keystone species.
It appears environmental stresses triggered the outbreak, Dr. Menge told PBS NewsHour. Some argue the main culprit is warming sea temperatures. But, the Oregon outbreak occurred during a period of upwelling, where colder water rose to the surface.
“It doesn’t mean necessarily that temperature is not involved, but it’s likely a much more complicated story,” Menge told NewsHour. His team is exploring the impact of ocean acidification. Along with colder water, upwellings can carry acidic waters from the ocean floor to the surface.