Your body is home to a unique collection of bacteria, viruses, and fungi that live in and on you, known as your microbiome. When everything is in balance, you feel good. But without your microbiome, you can get sick. The same applies to other animal kingdoms—including sea stars. If their microbiome is left intact, they can become vulnerable to infections such as the mysterious sea star wasting disease (SSWD), which can cause limb loss and, worse, disintegrate into jelly-like puddles. on the sea floor.
The disease appears to follow trends in warming water flowing north from Mexico to Alaska, explained Andrew McCracken, a Ph.D. student at the University of Vermont, who studies how animals adapt to deal with stressors in their environment. “Every year SSWD spreads a little further north, mainly in the summer months.”
Scientists have been searching for the cause of SSWD since 2013, when large-scale die-offs began. The leading theory is that the disease is likely the result of a complex interplay between environmental stresses such as warming water temperatures, lowering dissolved oxygen levels, and a pathogenic agent. McCracken is the lead author of a paper recently published in Frontiers in Marine Science which describes an imbalance in the microbiome in sea star skin samples that is often elevated before SSWD symptoms.
Sea stars, like humans, often have a healthy community of microbes on their skin that serves as a “first line of defense” against pathogens or microbes that might try to enter the body, McCracken explained. “They inhabit that niche and it’s important to fill it, preventing anything else from taking over.”
Problems occur when natural microbial communities are disrupted and opportunistic microbes enter, causing further imbalances, and opening the way for potential pathogens to enter. And environmental stresses can bring down entire communities.
“When we’re stressed, we’re more prone to illness and the effects of illness,” McCracken said.
Sunflower sea stars can be no different. Over the past decade, SSWD has wiped out about 90% of the West Coast’s giant sea stars. So many died that, in March, the National Oceanic and Atmospheric Administration applied to list the species for protected status. Sunflower sea stars are “keystone species”—those that help support entire ecosystems—so their disappearance could fundamentally change Pacific Coast marine life.
In his work in the lab of Melissa Pespini, associate professor of biology, McCracken studies how environmental stressors affect disease dynamics. But he’s not trying to determine the cause of SSWD (although he’s interning this summer with the Haikai Institute of British Columbia to do so)—rather, he wants to know if they can come back. In spring 2023, he was awarded a three-year National Science Foundation Graduate Research Fellowship to find out.
The multi-part project stems from earlier work done by McCracken and colleagues while analyzing the sea star’s microbiome. The team found a 1,200-fold increase in the presence of Vibrio—a genus of bacteria often associated with many marine diseases in sea stars affected by the wasting disease. They identified the possible culprit but did not find a definitive smoking gun.
McCracken will run a metagenomics test to identify all the bacteria, including Vibrio strains, that multiply with SSWD signs. The study will also examine how stable sea star populations are over time. However, sea stars are difficult to capture, and difficult to keep alive in a lab setting, prompting McCracken to use sea urchins as a model species.
“[Sea Stars and sea urchins] they’re both echinoderms, they have the same type of immune cells and their immune systems work the same way,” he said.
McCracken aims to test the short- and long-term resilience of sea urchins to multiple environmental stressors to determine the organisms’ potential to adapt, acquire immunity, and ultimately, rebuild their populations. population. She will hatch a sea urchin larva and expose it to higher water temperatures—both gradual increases and acute spikes to mimic natural events—and to a known larval pathogen. He will check which larva can survive the increase in temperature, survive the pathogen and, if one survives both stressors, determine if the selection of beneficial genes has occurred, suggesting the potential for adaptation. The results will help create a simulation that shows how evolution occurs over generations.
It’s possible that no useful genes will arise—that the changes are just too much, too fast. It is also possible that some traits that help individuals survive can be passed on to future generations.
For McCracken, who grew up in coastal Maine, the consequences of SSWD can be hard to imagine. He was drawn to the study of disease biology and ecology because of the changes he witnessed in the environment as habitats decreased and water temperatures increased.
“The marine environment is extremely fragile,” he said.
McCracken came to UVM because he wanted to do something to help save it. He set out to use his expertise to examine the effects of humans on wildlife and the ability of organisms to survive on a planet undergoing rapid change.
“The ultimate goal is to be able to predict the effects of global change on marine ecosystems, identify endangered species, and learn from those that demonstrate the resilience of our changing world,” he said.
Andrew R. McCracken et al, Microbial dysbiosis precedes signs of sea star wasting disease in wild populations of Pycnopodia helianthoides, Frontiers in Marine Science (2023). DOI: 10.3389/fmars.2023.1130912
Provided by the University of Vermont
Citation: Searching for resilience to sea star wasting disease (2023, July 19) retrieved 19 July 2023 from https://phys.org/news/2023-07-resilience-sea-star-disease.html
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