Warming seas may cause more disease, Cornell researchers say

By Erica Cirino, Safina Center Launchpad Fellow

It’s June 2013: A group of park rangers are walking down a peaceful strip of shoreline in Washington State’s famous Olympic National Park when they spot an alarming sight: dozens of shriveled, gooey-looking purple and orange sea stars trying to cling to a rock.

There’s something wrong, but the rangers are not quite sure what. And little do they know the problem is about to get much, much worse.

Since those first sick sea stars were found in Washington, millions more have been wasting to death all along the West Coast of the U.S., from Alaska to Baja California. A sea star disease epidemic of unknown magnitude decimated up to 90 percent of sea star populations in some parts of the Pacific Northwest between 2013-2014, and, while the epidemic has since slowed, sea stars are still dying.

Sick and dying sea star.  Credit: Oregon State University.

Recently, researchers have determined a virus causes the so-called sea star wasting disease. But just this month researchers associated with Cornell’s Ecology of Infectious Marine Diseases Research Coordination Network (EIMD RCN) have discovered why the virus had spread so rapidly and infected so many sea stars, especially during the 2013-2014 period: increased ocean temperatures.

“Temperature can be an incredible driving force for disease,” says Dr. Maya Groner, postdoctoral research associate at Virginia Institute of Marine Science and an author of the study. “This study emphasizes just how important temperature events like El Niño and climate change are when it comes to influencing disease.”

To learn more about how higher temperatures affect sea stars, they collected data on ochre sea star populations and ocean temperature at 16 sites in the Pacific Northwest from December 2013 to July 2015. They also carried out laboratory experiments on sea stars that investigate how temperature and life stage affected sea stars exposed to the fatal virus. In both the field and the lab, they noticed higher temperatures both increased sea stars’ risk of disease and the rate at which infected individuals died.

The sea star study is one of two published this month by researchers at Cornell’s EIMD RCN that reveal how warming seas harm many marine species. In the second study, the researchers have written that rising ocean temperatures correspond to an increase in disease in 24 marine species, including sponges, corals, sea stars, fishes, crustaceans, bivalves, turtles and sea grasses.

This link, the researchers say, highlights the importance of developing temperature-surveillance tools such as remote sensors to help monitor species’ health. Their study focuses specifically on how temperature surveillance tools could better forecast disease in the American lobster, an economically important species important to the Southern New England fishery.

Over the past few decades, the American lobster has been experiencing a population decline due to a deadly shell disease, which the researchers have found has become more prevalent thanks to rising ocean temperatures. Based on his group’s research, says Dr. Jeffrey Maynard of SymbioSeas and Cornell University, and an author of the study, as ocean temperatures continue to rise, the prevalence of this disease should also increase.

Healthy American lobster. The shells of diseased lobsters become weakened and scarred over time. Photo: Derek Keats

“That conditions will be increasingly conducive to lobster shell disease in coming decades is a cautionary tale,” says Maynard. “Marine disease is on the rise as sea temperatures increase under climate change resulting in increased disease susceptibility and pathogen virulence and the emergence of new pathogens.”

Ocean temperatures are only projected to increase into the future. Monitoring water temperatures can help alert environmental managers to possible disease outbreaks.

Legislation now on the table would provide a working group, data repository and fund for continuous monitoring of marine diseases. Those concerned about the health of marine species should support this and other legislation that provides resources for monitoring and responding to marine disease outbreaks.

“With this act, we would have more data, better data and better management practices,” says Groner. “Reducing outside stresses (such as pollution or sewage output) or changing fisheries policies (by reducing or changing quotas) could help keep disease down even with increasing ocean temperatures.”