Sea stars are iconic coastal creatures. They’re colorful and cling to rocks and mussel beds all along the coast. Everyone loves them.
But sea stars are dying out. And nobody really knows why. “Sea Star Wasting Syndrome” has gotten the attention of scientists and Newsweek alike. While much remains a mystery, here’s what we know—and what we don’t—about the growing threat to sea stars.
What It Is and How It Began
Sea Star Wasting Syndrome is a phenomenon where sea stars atrophy and die off, usually in clusters. It was first spotted in June 2013 at, ironically enough, Starfish Point, on Washington’s Olympic Peninsula and in British Columbia’s Howe Sound. Soon reports started coming in from the entire Pacific Coast.
The reports were all similar. Sea stars developed white lesions on their arms, which rapidly spread to the entire body. The sea stars took on a desiccated, hollowed-out look reminiscent of a sea star stranded too high in the tidal zone. Then they’d lose limbs. Sea stars will eliminate arms to contain infections, regrowing them late, but these sea stars lacked the health and energy to recover. The pattern spread among sea stars in an area until the population was largely gone. It began with many-rayed Sunflower Stars, and then appeared in the familiar Ochre Star and other species.
What’s Causing It?
Other Sea Star die-offs are not unheard of: they’ve occurred during El Nino years, when changes in weather patterns that create a shortage of food for mussels and clams in the eastern Pacific. Since mussels and clams are the primary food source for sea stars, sea star populations often crash as well.
But this decline is different, affecting millions of sea stars up and down the entire west coast of North America. The lesions found on sea stars make the likely culprit some kind of pathogen, virus, or bacteria. But other factors may be contributing.
One suspect is temperature. Sea star populations in warmer water, such as Southern California, have been nearly eradicated. Wasting syndrome has been later to arrive and slower to take hold in colder water and areas with swift ocean currents, such as Washington’s San Juan Islands. The pace of the syndrome also seems to increase as the weather warmed. This fits the pathogen theory, since microorganisms reproduce spread faster in warmer water than cold. Both seasonal weather variations and longer-range climate change trends could be factors. One theory is that the microorganism is waterborne and thrives in warmer seas. Another is that it is passed from one sea star to another either through contact when sea stars clump together.
How the pathogen is spread may be related to either water, food, or both. At a Santa Barbara aquarium, captive sea stars kept in tanks of filtered seawater drawn from nearby waters showed Wasting Syndrome symptoms the same time as their wild brethren in the sea a few hundred feet away, implying a waterborne transmission. Yet in another experiment at the same aquarium, one tank of sea stars were fed mussels from nearby, while another set was fed frozen squid. The mussel-fed sea stars got wasting syndrome, while those fed squid did not.
This raises the possibility that the syndrome may be transmitted through food. Mussels and clams, feed out of the water column, so this doesn’t rule out a waterborne pathogen. However, the shellfish may be concentrating whatever pathogen causes the wasting syndrome. And the pathogen itself is unknown.
The Ripple Effect
Another question is what will happen if sea star populations decline for a long time. While sea stars seem quite different from wolves, orca, and eagles, they all have one thing in common: they’re all apex predators occupying the top their food chains. Sea stars control the mussel and clam population, and are rarely eaten due to their tough exterior and lack of a meaty inside. In the complex world of tide pools, sea stars are the enforcers of the lower boundary of the mid-tide zone. they eat mussels, clams, and goose barnacles that descend to low enough for sea stars to get to them. With the border patrol gone, the mussels may expand their territory seaward. What would happen then? The mussels might intrude on the territory of sea urchins, which may lead to a regrowth of kelp forests. In areas where sea otters feed on urchins, the otters may find themselves needing a new food source, or may simply shift to eating the mussels. One thing is certain: the loss of a keystone species will result in wholesale changes in the tidepool world. Just what they are, we can’t say.
Marine biologists are racing to identify the pathogen, and genetic studies are underway at Cornell University, the University of Washington, and University of California at Santa Cruz. This may help determine whether Wasting syndrome is in fact one coastwide phenomenon or several smaller incidents in combination. This research may point the way to what humans can do to stabilize the sea star populations.
How You Can Help:
The primary need is for rubber boots on the ground. Beachgoers are well-positioned to spot instances of sea star wasting, take images and record locations. This information will help identify patterns in Wasting Syndrome that could lead to a better understanding of the causes, identify pockets of resistance, and help chart a way forward. Observers can enter data onto a site maintained by the University of Santa Cruz.
When you’re on the beach, keep your eyes open and your camera phone handy.