Our Sea Stars Are Dying. And No One Knows Why
Anyone can see the evidence on YouTube: a sea star (also known as a starfish) at the Vancouver Aquarium falling apart over seven hours in a one-minute time-lapse video. First, the middle of the star’s dark body flattens. Then, as the animal squirms all over the tank, its arms twist, pull free of its body and writhe independently. Soon after, the sea star dies. Seattle Aquarium staff veterinarian Dr. Lesanna Lahner has watched the video before, but still finds it unsettling from an ocean health perspective. “It’s quite creepy,” she says.
No one has yet determined the cause of the wasting disease that killed this sea star—and likely more than a million others on the West Coast. The deaths have been noted from Alaska to southern California since last August. That’s when divers began noticing piles of dead sea stars, many of them turned to mush, off the coasts of the Olympic Peninsula and Vancouver, B.C. At least a dozen species have been affected. Some of the hardest hit are also some of the most common, such as the sunflower star (Pycnopodia helianthoides), whose up to two dozen rays fan around its body like flower petals, and the five-armed purple, orange or brown species known as the ochre star (Pisaster ochraceus). Both kinds of sea stars can be spotted in Seattle’s tide pools and on dock pilings, scattered among the cylindrical sea anemones like x’s and o’s in a game of tic-tac-toe. The populations at many Puget Sound locations have been devastated, and so, too, have the exhibits at the Seattle Aquarium, which are maintained with Sound water lightly filtered through sand. “It started near the end of October, and within a month or two we’d lost most of our sea stars,” Lahner says.
Dr. Lesanna Lahner at the Seattle Aquarium, where sea stars in the touch tank may offer a clue as to what’s killing sea stars in the wild
While this is not the first time these echinoderms—in a phylum that also consists of sea urchins (including sand dollars) and sea cucumbers—have been struck by mass die-offs, most previous incidents were different in several ways. For one, they occurred at just a handful of sites, according to Ben Miner, a biology professor at Western Washington University who is surveying 30–40 sites in Washington state and collecting samples for study. This die-off dwarfs those events. “It’s never been observed geographically as widespread as we’re seeing it this time,” he says.
Drew Harvell, a professor of ecology and evolutionary biology at Cornell University, has been coordinating the collection of sick and diseased sea star samples since last summer. She says previous sea star die-offs were also more short-lived, taking place in warmer months and subsiding in winter. “I kept thinking that this was going to end,” she says of the months she spent studying the spreading disease through the fall and winter.
Instead, the disease continues to ravage sea star populations. As of mid-February, it was still hitting new sites—nearby, there were fresh reports from south Puget Sound and Whidbey Island, and in late February from Hood Canal. “It’s still very active,” Harvell says.
In Lahner’s lab, samples of sunflower sea stars killed by the wasting disease; Courtesy of Lesanna Lahner
Most previous outbreaks have also been limited to one or two species, not the dozen or so affected this time. Miner says that although sea stars look similar, many of the species belong to distinct groups that diverged many millions of years ago, and may not be very closely related, making the diversity of these sick sea stars more of a puzzle, and more of a concern. We don’t yet know whether this outbreak could kill an entire species, but the fact that the cause—whatever that might be—is deadly to so many is a troubling sign. “A pathogen with a very wide host range can be dangerous and could be a cause of species extinctions,” Harvell says. Some sites have already lost all their stars, and, even without extinctions, those sites may be without sea stars for years to come.
The broad geographic area, and the fact that much of this is happening underwater, make outbreaks difficult to track. Observers first began to see the disease in Puget Sound last fall. One early report reached Laura James, diver, filmmaker and codirector of Tox-Ick (tox-ick.org), a Puget Sound education effort. “One of my friends saw hundreds of dead starfish on the beach south of Fauntleroy ferry dock and texted me pictures,” James says. She regularly dives at the pier near Salty’s Seafood Grill on West Seattle’s Alki Beach, where she commonly spots hundreds of live sea stars on the underwater pilings. Soon after that text message, she went underwater and found her favorite dive site littered with dead starfish. “There were literally bodies piled on top of bodies,” she says. “It reminded me of war zone pictures.”
Local diver Laura James, at her regular dive spot near Salty’s on Alki, where she found countless dead sea stars. “There were literally bodies on top of bodies,” she says. “It reminded me of war zone pictures.”
Researchers are on the hunt for a cause. Marine invertebrates are sensitive to changes in ocean pH and temperature, so warming waters and ocean acidification could affect the stars, but Harvell says there’s no evidence linking either issue to the disease. They have also investigated harmful algal blooms, which, she says, tend to be more regional, but could play a role in “complicating the story.” Much less likely? Death due to pollution from the meltdown at Japan’s Fukushima nuclear power plant, a fear some in the public have expressed. “There’s been a lot of testing in Washington state waters and there are no higher levels of radiation, from everything I’ve seen,” Harvell says. “I don’t see any evidence that there’s anything from Fukushima that’s affecting this.”
One possible clue comes from the Seattle Aquarium touch tanks, where many children have their first experience looking close up at sea stars, sea cucumbers, sea urchins and other tide pool life. The water in those tanks is filtered with ultraviolet (UV) light to reduce microscopic pathogens in the water, and thus reduce the already low risk of possible infection for a child (or adult). The sea stars in the touch tanks appear to be less susceptible to the disease than those in other tanks. While she won’t rule out other possible causes, Lahner says this could point toward pathogens such as bacteria or viruses that can’t survive UV light.
There are other signs that also seem to point to those pathogens. Harvell’s colleague Ian Hewson, also at Cornell, is one of the world’s only virologists studying sea stars, and he is now analyzing the molecular sequences of hundreds of tissue samples from West Coast sea stars to locate an infectious agent.
Left: A healthy colony of sunflower stars, photographed last October at Croker Island, near Vancouver, B.C.; Right: Twenty days later, the sea stars have wasted away, leaving only white mats of bacterial ooze
Whatever cause is found, the loss of huge numbers of sea stars is certain to have an effect on the ecosystems where they once thrived. “It is a huge concern,” says Lahner, especially because sea stars are a keystone species—that is, a species with a significant impact on its environment relative to its abundance.
University of Washington zoologist Robert T. Paine coined the term “keystone species” (which applies to animals from elephants to sea otters), several decades ago, during his research on the ochre sea stars of Tatoosh Island off the Olympic Peninsula coast. That study showed that a relatively small number of the ochre stars maintain the balance of the ecosystems they inhabit. Sea stars species vary in what they eat—from mussels, and other shellfish, to snails, small fish, other sea stars and microalgae—but they are top predators, and the intertidal zone will be transformed without them, though we don’t yet know how.
In the case of Tatoosh Island, mussels took over and elbowed out competitors when the ochre star was removed.
With so much at stake, “We really want to get an answer for this outbreak,” says Lahner. One way the public can help assist researchers in learning how this disease is spreading is by reporting any dead or sick sea stars they find.
HELP REPORT SICK SEA STARS
Local divers Laura James and Lamont Granquist have created a map of all reported sites of dying sea stars at sickstarfish.com. They urge any divers and beach walkers who find what appear to be sick sea stars to take photos of the animals and upload them to social media websites with the hashtag #beachstarfish or #sickstarfish; those posts will automatically be added to the map. Members of the public with more detailed information to report about the sick animals can do so via the University of California, Santa Cruz website: data.piscoweb.org/marine1/seastardisease.html.
By the time scientists have an answer, there may be little they can do to stop current die-offs, but the information could help them figure out how to manage future outbreaks. It may also give clues that could prevent them from happening at all. For instance, if the virus or bacteria was brought in by coastal pollution or ballast water from ships, it could lead to a change in practices that would protect sea stars and perhaps other marine life.
James says the public reacts more slowly to mass deaths in the ocean than they would if this happened on land. “If we were seeing 12 different species of birds falling out of trees and dying, I think people would go nuts,” she says. “Because it’s underwater, it’s out of sight, out of mind.” (If sea stars were a favorite food of humans, like salmon, we might also respond more quickly.) And yet, she says, people feel a strong connection to these animals. “If you think about it, what was the first animal you saw on the beach? Or at an aquarium—what’s the kids’ favorite exhibit? The touch tank. People connect with them.”