Evidence that Microorganisms at the Animal-Water Interface Drive Sea Star Wasting Disease

Frontiers in Microbiology

Corresponding Author: Ian Hewson, hewson@cornell.edu 

Summary by Ethan Hackmeyer

Sea Star Wasting Disease (SSWD) is a fatal disease of starfish and other echinoderms that has led to severe declines in starfish populations beginning in the early 2010s. CEID member John Wares is a co-author on new research, led by Cornell University, that suggests the mechanisms of this disease are quite different from previously thought.

Early reports of SSWD suggested that it was caused by an infectious pathogen rapidly spreading among starfish populations. Starfish off the western coast of North America were showing the same symptoms; bloating, deflation, lesions, limb deformities and discoloration. However, new research suggests that environmental conditions that promote bacteria growth could share some of the blame, rather than a pathogen alone.

Over a five year period, researchers tested whether different properties of starfish made them more susceptible to SSWD, as well as how oxygen and organic matter levels affect SSWD prevalence. Starfish samples collected from large die-offs suspected to be caused by SSWD were also analyzed.

It was found that bacteria living in the biofilm on the surface of the starfish were creating toxic conditions, rather than directly infecting the starfish. These bacteria, called copiotrophs, feed on organic matter and use large amounts of oxygen during respiration. When conditions are ideal, these copiotrophs can quickly deplete the oxygen in the water around the starfish, “choking” it and causing it to exhibit symptoms of SSWD. Once one starfish dies of SSWD, the copiotrophs can feed off of the new organic matter, choking its neighbors as a larger oxygen-deprived region is created. If this effect scales as the researchers suspect, then copiotrophs could be causing the resulting mass die-off to look pathogenic in nature, despite not directly infecting the starfish.

The information gained from this study will be important in helping to predict and mitigate future die-offs. With copiotrophs being implicated as the main perpetrator of SSWD, the factors that cause their rampant growth — warm water and high organic material levels — can be monitored to assess the risk of a die-off occurring.  It is important to note, though, that there may be interactions between changing environmental conditions and an unrecognized pathogen. As climate change accelerates, however, these mass mortality events will likely occur more often, with starfish struggling to adapt to the changing climate in addition to copiotroph conditions being made more and more suitable.

Aquino et al, (2021). Evidence that Microorganisms at the Animal-Water Interface Drive Sea Star Wasting Disease. Frontiers in Microbiology 11. https://doi.org/10.3389/fmicb.2020.610009