The Oceanic Pandemic: Starfish and Microbes

A deadly starfish disease has rampaged the oceans turnings hundreds of starfish into goo. This ailment was first observed in starfish back in 2013. It can cause tissue to decay and cause the starfish to lose some of its limbs.

In lieu of this disease, Scientists explored differences in water temperature as well as possible pathogens that these starfish could have been exposed to, to find what was causing the oceanic pandemic. Scientists, however, found no major differences in the types of bacteria living among both the diseased and healthy starfish.

It wasn't until recently, that scientists discovered that this mysterious disease is not caused by a pathogen. These starfish are dying from deoxygenating bacteria that live among the starfish communities. Multiple types of bacteria near the starfish's skin are depleting the ocean's oxygen and thereby suffocating the starfish. The reason these microbes had initially gone undetected was that they were present among all species of starfish. Not all starfish are impacted by these deoxygenating microbes. Big starfish have a larger surface area to volume ratio and thereby have more places for the bacteria to deplete their oxygen and suffocate them. These large starfish, so far, make up 95% of all diseased starfish. The flatter and smaller starfish have a smaller surface area to volume ratio and thereby have fewer places for the deoxygenating microbes to suffocate them. These small starfish are largely unaffected by the deoxygenating microbe in nature. To ensure that these microbes were the cause of the starfish pandemic, scientists placed large and small starfish in deoxygenated tanks and observed the effects. 75% of large starfish in the depleted oxygen tank formed lesions on their limbs and the control group gained none.

How the starfish degrade and turn into gooey liquid is still unknown, but many scientists predict that mass cell death allows the starfish to shrink and succumb to the warm temperatures of the water.

This disease is not caused by a contagious pathogen but it can be passed on to other starfish in the surrounding areas. The sea stars with lesions in the deoxygenated tank produced organic matter that sparked additional bacterial growth on healthy starfish nearby.

Seeing the effects of deoxygenation on starfish has raised concerns for starfish survival in the midst of global warming. Warm water can not accommodate as much oxygen as cold water. As the ocean heats and the available oxygen depletes, starfish may begin to die even without the presence of deoxygenating microbes. This deoxygenating bacteria has introduced a new type of "disease transmission". Although these microbes don't invade the starfish's body they do act analogous to a deadly, airborne poison. Fighting this oceanic disease will be a challenge.

Sources:

C. A. Aquino et al. Evidence that microorganisms at the animal-water interface drive sea star wasting disease. Frontiers in Microbiology. Published online January 6, 2021. doi: 10.3389/fmicb.2020.610009.

I. Hewson et al. Densovirus associated with sea-star wasting disease and mass mortality. Proceedings of the National Academy of Sciences. Published November 17, 2014. doi: 10.1073/pnas.1416625111.