Time-Lapse Video Shows How a “Wasted” Sea Star’s Arm Dissolves Over an Hour
In 2013, the sea stars of the Pacific had their own version of a Walking Dead-style nightmare. From Mexico to Alaska, otherwise healthy stars seemed to literally rot away before scientists’ eyes from a degenerative disease, which some classified as an epidemic. Since then, the number of cases has tapered off, but the disease is still around. Scientists still haven’t nailed down the cause of this apocalyptic condition, though a team at the University of Vermont, who captured the disease on video, may have solved at least a part of the puzzle.
The video shows the progression of sea star wasting disease (SSWD) — a condition that literally causes the star’s flesh to rot away, sometimes in a matter of hours. In the first few seconds of this video, the disease is shown in greater detail on a poor, unsuspecting Pisaster ochraceus. At eight seconds in, a small lesion starts to form around this star’s arm, until the star literally leaves its limb behind as it moves away. Postdoctoral fellow Melanie Lloyd, Ph.D., who co-authored a study on SSWD published Wednesday in Scientific Reports, tells Inverse that this star was one of 37 that arrived at her lab completely healthy. Within two weeks, all but eight were either dead or close to it.
“This individual was healthy when the time lapse started and more or less dead when it ended 12-16 hours later. Progression of SSWD is very fast,” Lloyd says. “It was not uncommon at all to observe a star healthy one day and in pieces and near death the next morning.”
Lloyd’s paper suggests that the degeneration is caused by a radical shift in the microbiome of the sea stars. When the disease strikes, her analysis showed that the natural variety of microbes in the starfish tends to die off, allowing other harmful bacteria to take advantage of these newfound vacancies. As an example, the paper points to Tenacibaculum, a genus of bacteria that can cause lesions in other marine creatures.
Melissa Pespeni, Ph.D., a study co-author, adds that this is the first time they’ve looked to the sea star microbiome for the cause of this disease. Previously, one paper in the journal PNAS suggested it might be caused by a virus, though that proved true for only one species. SSWD affects over 20 species of sea stars.
“For many human diseases we’ve begun to understand that the microbiome plays an important role ‘in sickness and in health.’ We thought this might be the case too for sea stars given the large number of species affected and the large geographic spread of the disease,” she tells Inverse.
We’ve already established the role of the microbiome in certain autoimmune diseases in humans, but we’re also beginning to understand the role it may play in disease that affect other species too. SSWD may be a recent example, but Lloyd also points to black band disease in coral, which also causes disintegration in tandem with a microbiome shift.
This understanding comes a bit too late to help the stars that have already lost their lives to SSWD, but it may help those in the future, particularly the newer juvenile populations that are now tasked with restoring the population.
“There was serious concern about the longevity of populations of many species along the entire coast. Since the major outbreak, there has been a recovery of juvenile individuals but the population numbers have not recovered,” Lloyd adds.