Starfish slow to recover from disease outbreak

            When a University of Rhode Island undergraduate student tried to conduct a research project on starfish in 2011, she immediately ran into trouble when the starfish – more appropriately called sea stars – quickly began dying. The animals first became bloated, and within a day or two they were mushy and appeared to just melt away. It was one of the first East Coast observations of sea star wasting disease, which nearly wiped out the species from the coastal environment from Maine to New Jersey.

            Five years later, sea stars are still quite difficult to find in Rhode Island waters, though it appears that the die-off may be over. Whether they are beginning to recover their populations is another question.

Common sea star photo by Bill Frank

            “I think the disease is still out there, though I don’t know how intense it is any more,” said Adam Kovarsky, who manages the Save the Bay Exploration Center and Aquarium in Newport. “We still see sea stars with related issues now and again, but it appears that the population seems to be making a slight recovery from what it was. But it’s slight.”

            Kovarsky successfully kept the disease from infecting the 30 sea stars in Save the Bay’s aquarium for about two years, but eventually the disease found its way into his facility and all of the sea stars died.

            A few years before the disease was discovered, sea stars experienced an exponential population increase in Narragansett Bay. It wasn’t uncommon for Kovarsky to pull up 300 pounds of sea stars at a time with the fishing trawl net he uses in educational programs on the water. The year after the disease struck, he caught none. Today, Kovarsky said that sea stars are still mostly absent from shoreline habitats, though they are found in limited numbers by fishermen in Rhode Island Sound and in smaller numbers in the deepest parts of the Bay.

            The population increase just before the disease struck may have contributed to the outbreak, which is not an uncommon phenomenon. Niels-Viggo Hobbs, a doctoral student at URI who studies crabs and other shoreline creatures, said that rapid population increases often make animals more susceptible to disease, and the large numbers living nearly on top of each other make it easy for diseases to be quickly transmitted throughout the population.

            “All the sea stars people are finding now appear to be healthy,” said Hobbs, “so maybe all of those that were susceptible to the disease were killed off. The population is much, much lower now, but that may be just part of a natural cycle.”

Hobbs and other experts said that most of the sea stars found in the bay in the last year have been juveniles, while adults are still rare.

            What caused the disease is still uncertain, though researchers speculate that the pathogen may have been in the water for many years and was only triggered recently when changing environmental conditions reduced the sea stars’ immunity. Researchers from URI, Brown University and Roger Williams University worked together for several years to gain insight into the cause, but they were hampered by the challenge of finding many living sea stars to study. Caitlin DelSesto, the URI student who discovered the disease as an undergraduate, completed her master’s degree last spring studying the environmental conditions that may have helped to spawn the disease outbreak.

                   "Even throughout the course of our experimentation, some stars never seemed to succumb to the disease pathology, which lends hope to the idea that their numbers could recover," said DelSesto. "We do not know for sure what has been triggering the outbreak, so it is hard to say whether this stimulus -- like higher temperatures, differences in salinity or pollutants -- is still active in the ecosystem."

            The disease isn’t confined to the East Coast, however. As many as 40 different species of sea stars from Alaska to Mexico have also been killed by what is presumed to be the same or a similar disease as the one affecting sea stars in southern New England. West Coast experts meeting about the disease in Seattle in January called it one of the largest wildlife die-offs ever recorded, with 90 to 95 percent of some populations affected. Researchers there think it may be caused by a virus that became more harmful due to warming ocean waters.

            “An outbreak like this happened here back in the 1990s, and on the West Coast there were similar outbreaks in the 70s and 80s, and every time the population came back on their own,” said DelSesto in an interview in 2013. “This one seems particularly severe, and climate change may be making it worse, but hopefully they’ll come back on their own this time, too.”

This article first appeared on EcoRI.org on April 20.