Sea star population plummets at Shell Beach from mysterious wasting disease

dsneed@thetribunenews.comApril 5, 2014 

The shoreline below Beachcomber Drive in Shell Beach looks like an ideal place to go tide pooling.

A bedrock shelf covered with brown algae gently slopes into the surf, creating many nooks and crannies for sea life to live.

But one iconic tide pool species, the ochre sea star, is almost entirely missing.

For the past year, starfish along the coast from Alaska to Mexico and portions of the East Coast have been falling victim to sea star wasting syndrome, a little understood disease that has caused numbers of the animals to plummet in many California locations.

Christy Bell, a marine biologist at UC Santa Cruz, monitors tide pools twice a year at eight locations along San Luis Obispo County’s coastline. Bell and her team recently scoured a large section of tide pools at their Shell Beach monitoring site during low tide and found only two ochre sea stars.

“It’s really bad,” she said shaking her head. “We were hoping we’d find more.”

This stands in stark contrast to 20 years ago, when monitoring at the site began. At that time, the Shell Beach site had some of the highest densities of sea stars anywhere along the county coastline, Bell said.

Sea star numbers locally have dropped off dramatically in the six months since the last surveys were done. Last fall, Bell and her team found 12 sea stars at the Shell Beach site with two of them showing signs of the wasting disease. This spring, there were only two.

On the positive side, the two they did find appeared healthy. Similarly, the number of sea stars at a monitoring site at Vandenberg Air Force Base plummeted from more than 300 in the fall to 12 this spring.

Precipitous declines in sea star numbers have also been recorded at two other monitoring sites in San Luis Obispo County: Hazard Canyon Reef in Montaña de Oro State Park and Point Sierra Nevada in Hearst San Simeon State Park. Lower levels of the disease have been observed at many other beaches.

“The disease is very virulent,” Bell said. “Sunflower sea stars in aquariums have died only 24 hours after contracting the disease.”

Storms also a factor

Wasting disease is not the only factor in the sea stars’ decline. Heavy El Niño storms in 1997-98 wiped out many mussel beds in Shell Beach and caused sea star numbers to fall. Mussels are a prime food source for starfish.

The wasting disease infestation, which began last summer, has further devastated the remaining sea star population. In all, 15 species of sea stars are affected by the disease.

There are 200 tide pool monitoring locations along the West Coast where researchers document a variety of species in addition to sea stars. These include acorn barnacles, California mussels, golden rockweed, turf weed and surf grass.

The monitoring is used to track population trends and could provide baseline data in the event of an oil spill or some other natural or man-made disaster that damages tide pools.

The cause of the wasting disease remains a mystery. Researchers at Cornell and other universities are working to identify the pathogen causing the disease. Bacteria, viruses and protozoa are all possible causes, said Pete Raimondi, chairman of the Department of Ecology and Evolutionary Biology at UC Santa Cruz’s Long Marine Lab, who leads the tide pool monitoring program.

The disease begins with lesions on the starfish that become infected. Tissue decay around the lesions causes the sea stars’ arms to fall off, and the animals die within a matter of days.

“It’s like a lot of diseases; something compromises the animal, and a secondary infection does the main damage,” Raimondi said.

Researchers suspect that the disease might be linked to higher ocean water temperatures. But the fact that the disease is found from Alaska through California in locations of varying temperatures is causing them to rethink that theory.

“By the fact that it’s so widespread, we’re just not sure it’s warm water,” Bell said.

Beloved species

Wasting disease has generated a lot of attention among scientists and the general public alike. The public is interested because starfish, particularly ochre sea stars, are the one species most people think of when they think of tide pools.

“Sea stars are the most charismatic intertidal species,” Bell said. “They are bright and colorful and people know what they are.”

Marine biologists are interested in the wasting disease because it has the potential to significantly alter tide pool ecosystems.

Ochre sea stars were the basis of the keystone species concept in wildlife biology — the idea that the effect of some species on their ecosystem is vastly disproportionate to their abundance.

Specifically, removal of ochre sea stars from tide pools would allow California mussels — their main prey species — to dominate tide pools, forcing out other species and reducing the pools’ biodiversity.

“Without ochre sea stars, the species composition of rocky intertidal areas is expected to change very significantly,” Raimondi said.

Probably not Fukushima

One of the most common questions researchers get from the public is whether the disease is the result of radiation from the March 2011 nuclear power plant disaster in Fukushima, Japan. Bell and other researchers say they do not think radiation is the cause.

“As a scientist, you don’t want to exclude anything, but because the disease is also on the East Coast, we don’t think it’s Fukushima,” Bell said.

The public can help researchers track sea star wasting disease. Anyone interested in reporting sightings of sea stars, both healthy and sick, can fill out a report by going to this sea star monitoring page on the UC Santa Cruz website.

“We only have so many researchers for the entire coast, so it is very good to have help from the public,” said Melissa Redfield, a marine biologist on Bell’s team.

Bell and her team will be back in October and November for another round of monitoring. The long-term prognosis for sea star populations is unknown pending further monitoring and identification of the exact cause of the disease, Bell said.

“Historically, there have been more sea stars in the fall than the spring,” she said. “So we are hoping we will find a few more then.”

OCHRE SEA STAR FACTS

Scientific name: Pisaster orchraceus

Description: Large starfish with five stout, tapering arms

Color: Mostly ochre and purple

Habitat: Wave-washed rocky shores from Alaska to Baja California

Prey: Mussels

Predators: Sea otters and gulls

Life span: Up to 20 years

Significance: The most common large, intertidal sea star on the West Coast

If you see one: Admire its beauty and leave it alone

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