In 2013, the lives of millions of starfish were mysteriously destroyed. Arms that were once strong, find arms seeking nourishment, shrinking and tearing them away from the rest of their bodies and melting into a sick goo.
“There were arms everywhere,” said ecologist Drew Harvell The West Baylast year was Ed Yong. “It looked like an explosion zone.”
The remnants of these animals, which are usually able to regenerate their own arms, were scattered across the west coast of North America, in one of the largest wildlife mortality events ever reported. never recorded. More than 20 species of starfish were extinct.
In some areas, a sunflower star (Pycnopodia helianthoides) numbers fell by about 90 percent on average in weeks, a loss that saw this once common and plentiful disappearing from most of its range in a few years.
It was the culture that caused this consuming sea star (SSW) to even capture stars in captivity, killing individual animals within days.
Leg de Pisaster ochraceus different from starfish consumption syndrome. (Elizabeth Cerny-Chipman / Oregon State University / CC BY-SA 2.0)
This led scientists to suspect that a type of pathogen, such as a virus or bacterium, was suffering from these amazing sea creatures. However, subsequent investigations revealed the main suspect was viral.
Meanwhile, more starfish deaths followed across the globe, including half a world away in Port Phillip Bay, Australia.
Now San Francisco State University marine biologist Citlalli Aquino and colleagues have finally revealed the mystery, showing that something much more complicated was going on.
By comparing the types of bacteria within healthy starfish and those suffering from the disease of malnutrition, the researchers found bacteria that thrive in low-oxygen environments in abundance. in the sick animals, as were copiotrophs – bacteria that thrive on nutrient-rich environments.
Back tests in the laboratory showed that water spillage of oxygen caused melting wounds in 75 percent of starfish. Adding too much nutrients or phytoplankton to the water caused the health of the starfish.
By reviewing print samples from the 2013 event, the researchers found too much nitrogen – a sign that these animals were suffering from death.
“Starfish distribute oxygen over their outer surface through tiny structures called papulae, or skin gills,” explained Cornell University marine microbiologist Ian Hewson. “If there isn’t enough oxygen around the papulae, the stars can’t breathe.”
These microorganisms do not directly cause disease, but they do steal the oxygen supply of starfish when higher levels of organic matter cause the microbes to grow. As a result, the starfish literally drown in their own environment. Their decaying bodies then boost nutrients to the microbes, creating a horrible feedback loop of starfish death.
Aquino and the team noted that most SSW events are reported in late autumn or summer, when phytoplankton that increase nutrient levels in the water through photosynthesis are more abundant.
Warmer temperatures are known to drive phytoplankton blooms, and the starfish consumption event in Australia followed the longest and most intense heat wave on record. Starfish litter events elsewhere have also led to rising sea temperatures.
“Warmer waters can’t contain as much oxygen [compared with colder water] just with physics alone, “Hewson told Erin Garcia de Jesus at Science News.
None of this is going well for our future on a warming planet.
Vermont University biologist Melissa Pespeni, who was not involved in the study, said Science News this complex tangle of biological and environmental factors “is kind of a new idea for [disease] transmission. “
The devastating effects of the loss of these precious stars of the ocean have already spread out across entire ecosystems. The sunflower star is a ferocious predator with up to 24 arms that can go as far as 1 meter (3.3 ft), feeling its way across the seabed for sea urchins, snails, and other invertebrates. .
Without sunflowers and other starfish keeping an eye on sea urchins, these strawberries are eating their way through large kelp forests. By 2016, sea urchins had already reduced kelp numbers by 80 per cent in some areas, reducing those forests that were once flooded.
“This is a very clear example of a steep waterfall, which is an ecological domino effect triggered by changes at the end of a food chain,” said Isabelle Côté, a marine ecologist at Simon Fraser University, who studied its findings. after last year’s environment.
“It’s a strong reminder that everything is connected to everything else.”
This research was published in Limitations in Microbiologismy.