Starfish in San Luis Obispo County are suffering from a disease that has killed off more than half their population in some locations.
The disease, called sea star withering syndrome, was first detected last June and has quickly spread throughout the West Coast. It has been detected in all 10 tide pool sites in the county that are monitored by scientists with the Multi-Agency Rocky Intertidal Network.
“The decreases in sea star numbers have been pretty bad for every site that we’ve looked at in San Luis Obispo,” said Pete Raimondi, a marine biologist at UC Santa Cruz who is the lead investigator into the disease.
Monitors have not had a chance to do a complete monitoring at all sites in the county. But for those that have been fully monitored, the losses are 50 percent or more.
Another round of monitoring locally is scheduled for March and April. Monitoring sites in the county are spread along the coast from Piedras Blancas to Pismo Beach.
Sea stars, often called starfish, are some of the most common and popular animals found in tide pools. Hardest hit by the disease are ochre sea stars, which are the most abundant tide pool sea stars and are usually orange or purple. In all, 12 species are affected.
The cause of the disease is an unidentified pathogen that causes the animals to look deflated or have unnatural twisting to its arms. The disease then progresses to a bacterial infection that often leads to loss of arms and death.
“It’s like a lot of diseases, something compromises the animal and the secondary infection does the main damage,” Raimondi said.
The long-term outlook for sea stars is unknown. It is unlikely that the species will go extinct, but a large-scale loss of sea stars could change the species composition and ecosystem of tide pools.
Ochre sea stars are considered a keystone species because they are so dominant in tide pools. In the past, the loss of a dominant marine species has caused dramatic ecosystem-wide changes.
“The disease does not seem like it has stopped,” Raimondi said. “We are not sure if we are at the beginning, middle or end of it.”
Many universities and scientific agencies are researching sea star withering syndrome in an attempt to better understand it and fill in gaps in data. One of the main focuses is determining the exact cause of the disease.
For more information, go to www.seastarwasting.org.