SEATTLE -- A mysterious killer is wiping out sea stars along the entire West Coast of North America, with 20 species affected.
Called Sea Star Wasting Syndrome, the outbreak hitting the coast from Alaska to Mexico was first reported last summer from Olympic National Park in Washington and has continued to take out sea stars with merciless efficiency. Entire ecosystems might reshuffle as the top predators of the near shore succumb. As summer draws people to beaches, a beloved sea creature is dissolving before our eyes.
Katie Pyne and Haila Schultz, student researchers at the University of Puget Sound, were shocked as they surveyed sea stars this week at Alki beach. "It's just melting," Ms. Pyne said of a purple sea star disintegrating before her eyes. The smell of rotting flesh filled the cove along a jetty, and sea stars dripped from the rocks in a slow-motion fall to their deaths.
The devastation sickened Lisa Keith of West Seattle, a volunteer beach naturalist with the Seattle Aquarium. "As a beach lover, it was disturbing; everything was so gooey and drippy and falling off the rocks and turning into bacterial mats, I thought I would just leave the beach," Ms. Keith said.
Affected sea stars typically first contort and twist, and white lesions appear on their bodies. Their usually firm, meaty bodies deflate and waste away. Arms fall off and walk off on their own. The animal loses its ability to hold on to rocks or pilings. Its body falls apart in pieces and finally dissolves. Within weeks, only a ghostly white print will remain, and then nothing at all. Entire communities are wiped out, said West Seattle diver Laura James, whose underwater videos vividly document the devastation of the disease.
"It's a complete decline of sea stars at all of our dive sites and beaches," she said. She sees a loss not only of biodiversity but a beloved animal. "In addition to the environmental impact, there is this human issue, which is almost more important to me," Ms. James said. "They are that ambassador to the underwater world."
Experts seeking to understand the outbreak used descriptions scientists rarely use: unprecedented, scary, disgusting, heart wrenching.
"This event is unprecedented; we have never seen a wasting event of this magnitude, and we really don't know what is going to happen," said Drew Harvell, a marine epidemiologist from Cornell University based at Friday Harbor Labs and part of a nationwide team of researchers working to crack the mystery of what's causing the die-off. "We don't know the why of this event yet."
Is it a bacterial infection? Are warming waters triggering it? A virus? Some combination of the three?
"I am very concerned about warming waters," she said. "We are seeing more sickness in warmer waters, and we are at record temperatures.
Scientists are homing in on the culprit.
"We have evidence there are infectious agents involved in this and evidence that there is temperature sensitivity, but how it fits together is still a mystery," Ms. Harvell said
Scientists are reaching out for help, asking people to note where they see dying starfish when they are out on the beaches this summer. "There is nothing we can do to stop this, but if we learn all we can from this, we may be able to spot the next thing or identify places of resiliency to consider for future marine reserves," Ms. Harvell said.
Bruce Menge, professor of marine biology at Oregon State University, Corvallis, said while Oregon was unscathed last year, sea stars are taking a beating there now, with as much as 80 percent of some populations wiped out. "It is kind of a frantic time for us," Mr. Menge said. "Scientists love these kinds of mysteries, but it is a heart-wrenching thing to see this kind of die-off."
The consequences could be far-reaching. Sea stars are keystone predators, determining the distribution and composition of the ecological community they dominate.
The sunflower star is a master of the subtidal zone. Growing as big as a garbage can lid and cruising along at 3 feet a minute on as many as 24 legs outfitted with 15,000 tube feet with shell-crushing suction power, it is a carnivore to be reckoned with. Snails slither for their lives, and even spiny sea urchins are demolished when Pycknopodia helanthoides goes on the hunt.
Because of their dominant role in the ecosystem, the devastation of sea star populations could lead to a reshuffling of the food web and restructuring of entire communities in what ecologists call a "cascade effect."
That's already underway in the waters of Howe Sound, off Vancouver Island, notes Jeffrey Marliave, vice president of marine science at the Vancouver Aquarium. The die-off of sea stars in Howe Sound has led to an explosion of its favorite prey, green sea urchins, whose populations now are devouring seaweed that spot prawns need for nursery grounds in their first year of life.
"We are seeing zero counts of prawn," Mr. Marliave said. "This cascade effect is bigger than the die-off. It is affecting the whole ecosystem.
Mr. Marliave doesn't point the finger to human causes, at least not yet. Populations of sea star were so dense that he said he was not surprised to see a correction. "We went for a good decade with incredible overpopulation; the crowding was incredible," Mr. Marliave said. "I'll confess at first I was thinking, 'Hallelujah, something finally is controlling them,' but this is a little overboard. It is scary how badly things are going."
Staff at the Seattle Aquarium were among the first to notice the die-off last fall, when even the sea stars in its tanks, which live in recirculating water from Puget Sound, started to sicken. Staff veterinarian Lesanna Lahner has been collecting samples so Cornell scientists can analyze them.
"We have seen massive die-offs, pretty much 100 percent mortality under our pier We have never seen anything at this scale. It's unprecedented, and we are very concerned. It's pretty scary," Ms. Lahner said. One bright light is the large number of young sea stars burgeoning this year. "We are hoping they will grow up and not die as soon as they get to be adults."
Some scientists wonder if the die-off is a sign of things to come. With climate change, will a warmer ocean be a sicker one?
Carolyn Friedman, professor in the school of aquatic and fisheries sciences at the University of Washington, says while what's killing the sea stars isn't yet understood, with other animals, temperature has been part of the sickness equation.
Whether abalone in California or oysters on the east coast, when waters warm it stokes the metabolism of both the animals and the pathogens that sicken them in an arms race that turns lethal for the animal. Warming of just one degree can trigger massive mortality events taking out 99 percent of the black abalone she studies in California, Ms. Friedman noted.
Yet temperature didn't kick off the outbreak in Oregon, where Mr. Menge notes that water temperatures have been normal even where sea stars are dying in droves. So whether temperature is involved in the sea stars' plague is not yet clear.