Have you seen fewer sea stars lately? Scientists are still working out why

Starfish populations decimated by the onset of a wasting syndrome six years ago continue to make a comeback in parts of California, but recovery remains stilted along the Central Coast.

And while sea star wasting syndrome is “probably the best studied marine disease ever,” researchers still don’t definitively understand the causes behind it, said Peter Raimondi, a professor in the Ecology and Evolutionary Biology Department at UC Santa Cruz.

What is sea star wasting syndrome?

According the Multi-Agency Rocky Intertidal Network (MARINe) website, sea star wasting syndrome was noticed first by researchers in Washington state in June 2013 as masses of sea stars began dying on the Pacific coast.

Melissa Douglas, an intertidal associate research specialist at UC Santa Cruz, recently described the affliction.

“Usually we first see lesions on the star,” Douglas explained in a recording she made for high school students. “Often they begin to lose arms, and many times they turn into mush and basically look like they are disintegrating — all over a quick span of time, sometimes just a few days.”

More than 20 different species of sea star ranging from Southern California to Alaska have been affected by this wasting event.

A bat star on the rocks at low tide, only three were observed in a recent informal survey of Cayucos tide pool. Once commonly found in tide pools sea stars have been impacted by wasting syndrome from Alaska to Southern California reducing their numbers. 7-8-2019 David Middlecamp David Middlecamp dmiddlecamp@thetribunenews.com

Understanding the cause of the disease

Raimondi was part of a team that published research in 2014 in the Proceedings of the National Academy of Sciences that first suggested a virus could be at fault for the wasting syndrome — perhaps one that had impacted sea stars in the past.

The same team completed further work and found that explanation didn’t apply for most of the affected species. “There’s less certainty about what the cause was,” Raimondi said.

While bacteria has been confirmed as the ultimate cause of death for many sea stars with the wasting syndrome, it’s unclear what makes the sea stars so susceptible in the first place.

Raimondi suggested there may be possible environmental influences — such as temperature or other bacterial infections that create more sensitivity to this current bout of wasting. But, he said, it’s likely complicated.

There have been similar sea star die-off events in past decades, but Raimondi said the current instance is unusual in geographic scale.

Past occurrences of wasting in Southern California often haven’t extended beyond Point Conception in Santa Barbara County. These prior events were more obviously connected to warming waters, and didn’t impact so many sea star species.

Intertidal species, like the ochre sea star, can be found in tide pools like this one — though they are harder to find after the onset of sea star wasting syndrome. David Middlecamp dmiddlecamp@thetribunenews.com

How are starfish doing in SLO County?

Though results are still incoming from monitoring efforts in 2019, Raimondi provided a general overview of the state of sea stars in San Luis Obispo County. While survey efforts range from Mexico to Alaska, local recovery continues to be patchy.

In intertidal areas within San Luis Obispo County, numbers of the ochre sea star remain low. This species is an important control of mussels that can overwhelm tide pool habitats when ochre stars aren’t present.

Influxes of baby sea stars, including the ochre sea star, documented all along the Pacific coast in the year or two after the start of the wasting event gave Raimondi hope that local populations would see more recovery. “But that really hasn’t manifested,” he said.

According to Raimondi, survival for these little starfish can be a struggle even in the best of times.

A crab patrols the tide pools of Cayucos. Once commonly found nearby, sea stars have been impacted by wasting syndrome from Alaska to Southern California, reducing their numbers. David Middlecamp dmiddlecamp@thetribunenews.com

In rocky shore areas that remain under water and are home to habitats such as kelp forests, there has been “no recovery at all” of sunflower stars except in Washington state and locations father north, he said.

To his knowledge, Raimondi said, there has been no recent reports of sunflower stars found in this area.

That sea star, which has a radial crown of 16 to 24 arms and can be a half meter or more across, is a “voracious predator,” Raimondi said.

Raimondi said some in the scientific community attribute the loss of some kelp forests to the absence of sunflower stars and their control of sea urchins.

Sea urchins are efficient grazers on kelp, and can mow kelp forests down to leave areas referred to as “urchin barrens,” which disrupts the existing ecological community.

How to help monitor sea stars

Because the scientists and organizations who monitor and study the syndrome in sea stars have limited resources and personnel, people visiting tide pools are an important source of data.

Raimondi said that kids are especially adept observers and were instrumental in alerting scientists to the presence of juvenile sea stars seen soon after the onset of wasting syndrome.

Want to contribute to monitoring efforts? Submit your observations to the Sea Star Wasting Syndrome Observation Log at gordon.science.oregonstate.edu/sea_star_wasting/observation_log/new.

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