In 2013, the lives of millions of starfish were mysteriously extinguished. The limbs that were once strong, searched the arms for food, wiped and broke off the rest of the body and melted into a sick goo.
“There were weapons everywhere,” said environmentalist Drew Harvell AtlanticEd Yong is last year. “It looked like an explosion zone.”
The sad remains of these animals, which are usually able to regenerate their own limbs, have been scattered along the entire west coast of North America, in one of the largest mass wildlife mortality events on record. ever. More than 20 species of starfish have perished.
In some areas, the sunflower star (Pycnopodia helianthoides) populations have declined on average by about 90% in weeks, a loss that has seen this once common and abundant species disappear from most of its area in just a few years.
The culprit who caused the scattering of this starfish (SSW) even reached the starfish in captivity, killing individual animals in a few days.
Foot of Pisaster ochraceus disintegrating from starfish wasting syndrome. (Elizabeth Cerny-Chipman / Oregon State University / CC BY-SA 2.0)
This has led scientists to suspect a kind of pathogen, such as a virus or a bacterium, that infects these amazing sea creatures. However, subsequent studies exonerated the main viral suspect.
Meanwhile, several starfish deaths have followed around the world, including half a world away in Port Phillip Bay, Australia.
Now, San Francisco State University marine biologist Citlalli Aquino and his colleagues have finally revealed the mystery, pointing out that something much more complicated is happening.
Comparing the types of bacteria in healthy starfish and those suffering from wasted disease, the researchers found that bacteria that thrive in low-oxygen environments were abundant in diseased animals, as were copiotrophs – bacteria that like nutrient-rich environments. .
Laboratory experiments have confirmed that depletion of oxygen water has caused tissue melting damage to 75% of starfish. Adding excess nutrients or phytoplankton to the water also caused the starfish’s health to decline.
Reanalyzing tissue samples from the 2013 event, the researchers detected excess nitrogen – a sign that these animals had suffocated to death.
“Starfish diffuse oxygen to their outer surface through small structures called papules or gills of the skin,” said Ian Hewson, a marine microbiologist at Cornell University. “If there is not enough oxygen around the papules, the starfish cannot breathe.”
These microorganisms do not directly cause disease, but steal the oxygen supply of starfish when high levels of organic matter cause microbes to bloom. As a result, starfish are literally drowning in their own environment. Then, their decaying bodies further increase the nutrients of the microbes, creating a horrible feedback loop of starfish death.
Aquino and the team observed that most SSW events are reported in late fall or summer, when phytoplankton that increase nutrient levels in water through photosynthesis are more abundant.
Lower temperatures are known factors for phytoplankton flowers, and the event of the loss of starfish in Australia followed the longest and most intense heat wave on record. Events wasted by starfish elsewhere also followed rising sea temperatures.
“Warmer waters cannot have as much oxygen [compared with colder water] only through physics, “Hewson told Erin Garcia de Jesus at Scientific news.
None of this bodes well for our future on a warming planet.
University of Vermont biologist Melissa Pespeni, who was not involved in the study, said Scientific news this complicated tangle of biological and environmental factors is “a new kind of idea for [disease] transmission.”
The devastating repercussions of the loss of these precious starfish are already echoing in entire ecosystems. The sunflower star is a voracious predator with up to 24 arms that extend up to 1 meter (3.3 ft), feeling its way to the bottom of the sea to throw sea urchins, snails and other invertebrates.
Without sunflowers and other starfish that do not keep sea urchins under control, these herbivores eat their way through gigantic summer forests. By 2016, sea urchins have already reduced algae populations by 80% in some areas, decimating these once thriving underwater forests.
“This is a very clear example of a trophic 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 investigated the environmental consequences last year.
“It’s a clear reminder that everything is related to everything else.”
This research was published in Frontiers in Microbiologyand.