During the height of the sea star die-offs in 2014, millions of stars up and down the West Coast were wasting away. At the same time, sea surface temperatures in the northeast Pacific Ocean were the warmest recorded in decades.
Scientists suspected a connection.
Now in a study published Monday, scientists are confirming that warm temperatures played a part in what’s being called the single largest, most-geographically widespread marine disease that's ever been recorded.
Researchers analyzed logs from temperature sensors in Puget Sound and on the outer coast of Washington and compared them with extensive sea star monitoring data from surveys before, during and after the outbreaks. They found evidence that as water temperatures rose, so did the risk of starfish succumbing to the wasting disease.
They also conducted lab experiments, holding starfish in aquarium tanks at varying temperatures between 12 to 19 degrees Celsius. Starfish in warmer tanks died more quickly than those in cooler tanks. Juveniles took longer to show signs, but died immediately once lesions appeared.
“That was really direct evidence for the role of temperature at making them die at a faster rate,” said Drew Harvell, a Cornell University professor who co-author of the study. Harvell also teaches at the University of Washington’s Friday Harbor Labs on San Juan Island, where much of the field monitoring data was collected.
Researchers also found a correlation between the size of the sea star and wasting disease. Smaller stars seemed to have a greater chance of withstanding the disease than larger stars, said Joel Elliott, a marine ecologist and invertebrate zoologist with the University of Puget Sound, who co-authored the study.
Elliott, who has been monitoring starfish in South Puget Sound since 2005, said he used to reliably see hundreds of stars.
Now, very few stars remain. But in a low-tide survey last week, Elliott said researchers found evidence of ochre stars (Pisaster ochraceus) and mottled stars (Evasterias troschelii) that seemed to have survived the die-offs.
“They looked relatively healthy. Some looked like they had lost arms and were re-growing them,” Elliott said. “It’s possible that they dropped arms and were able to overcome the disease.”
The next step, Elliott said, is for researchers to look at the stars that have survived to see whether they are in fact immune to the disease and figure out how they managed to survive.
Katie Campbell is the EarthFix managing editor for video and a seven-time Emmy® Award-winning producer/photographer at KCTS 9. She covers environmental issues of the Pacific Northwest. Katie has earned national awards for her role in the documentaries Undamming the Elwha, COAL and Glacier Caves, and is the 2015 winner of the prestigious Kavli Science Journalism Gold Award from the American Association for the Advancement of Science for her story Is Alaska Safe for Sea Stars?
Katie grew up on a flower farm in southern Minnesota. After completing her undergraduate degree in journalism at St. Catherine’s University, she worked as an enterprise reporter at daily newspapers in Minnesota and Florida. She holds a master’s degree in narrative journalism from the University of Oregon. Prior to joining KCTS 9 and EarthFix, Katie was an instructor at the University of Oregon School of Journalism and Communication.
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