SANTA CRUZ — For the past two years, a mysterious disease has melted millions of sea stars along the West Coast into goo.
Consequences of the outbreak appear already at play as the sea star’s spiky cousin, the sea urchin, is thriving in Central California waters, but showing signs of dying down south.
While no one knows what exactly triggered the densovirus that likely caused the sea star epidemic, which scientists call one of the largest marine disease outbreaks ever recorded, it has set off a reshaping of the coastal food web.
“The virus has been around for at least 70 years,” said Peter Raimondi, a professor of biology at UC Santa Cruz who’s been studying the so-called “wasting disease.” “What we’re doing now is trying to understand if there’s environmental factors, such as warmer temperature or acidification, associated with the onset of the disease.”
Starfish are important predators in tide pools and coastal waters. If they continue to die in mass quantities, their prey — a smorgasbord of snails, mussels, clams and sea urchins — could spiral out of control and affect other ocean life.
That’s what scientists are beginning to see now with urchins, who are emerging from the rocky crevices from which they normally hide, filling the void left by a drastic loss in starfish numbers.
Similar die-offs have happened before in the 1970s, 1980s and 1990s, but never before at this magnitude and stretching over a wide geographic area.
This current epidemic has wiped out at least 20 different species of starfish, Raimondi said, including Pycnopodia helianthoides, commonly known as the sunflower sea star. One of the largest species and well-armed with 24 limbs, it was a main predator of red and purple sea urchins, and could consume one whole.
With the coast clear and more of its food floating around than usual, urchins now are covering the Monterey Bay Area seafloor in droves, resembling red and purple pincushions. Scientists suspect the urchin boom could spiral out of control into the deforestation of Central California’s giant kelp forests.
Urchins can still eat drifting kelp while safely tucked away from predators inside rocky reefs. Like leaves falling from trees, blades of kelp litter the seascape.
“The algae is brought to them by the currents, so they can just sit there and feed on the kelp without exposing themselves,” said Mark Carr, a professor of ecology and evolutionary biology at UC Santa Cruz. “In the absence of these predators, these urchins change their feeding behavior from just sitting in these cracks. They get up, and they storm around the rocky reef. They eat everything in their path.”
The greater ecosystem stands to lose if urchins mow down stands of seaweed.
“The physical structure of the kelp creates habitat for lots of other little animals like fish and invertebrates,” Carr said. “And that algae is also fed on by invertebrates grazing the forest.”
Without the sunflower sea star, the sea otter is the only predator to keep the surplus of urchins in check. The spiky puffs are among the whiskered animal’s favorite foods.
“But there’s only so many otters,” Carr said. “Sea otters are picky, and an otter that’s feeding on snails will be very reluctant to begin feeding on sea urchins.”
The starfish wasting syndrome has painted a different story south of Point Conception, where urchins now seem to be wasting away too.
Though the dying urchins express hallmark signs of the disease — losing their spines and coloration — scientists don’t know if the same virus is at fault.
“It maybe that environmental conditions that are stressing the sea stars that made them susceptible may also be stressing the sea urchins,” Carr said. “It’s not clear yet, but we’re trying to figure that out.”
He said sea urchins in Southern California might already be at their thermal limit.
Like an abundance, however, an absence of urchins also could reverberate throughout the food web. Its predators, both in the water and human, won’t bode well if they die in mass quantities. Anglers fish for other economically important species that prey on urchins, such as the spiny lobster and sheephead fish. And red sea urchins that land on sushi menus is big business in California, valued at $40 million.
“We’re beginning to see deaths in just small amounts,” David Goldenberg, director of the California Sea Urchin Commission said of the urchins in Southern California. “It’s certainly something that we’re going to be watching.” —— (c)2015 the Santa Cruz Sentinel (Scotts Valley, Calif.) Visit the Santa Cruz Sentinel (Scotts Valley, Calif.) at www.santacruzsentinel.com Distributed by Tribune Content Agency, LLC AMX-2015-04-07T05:17:00-04:00
