In 2013, the lives of millions of starfish mysteriously died out. Limbs that were once strong, explored the arms in search of sustenance, shrank and moved away from the rest of the body and melted into a diseased wrapper.
“There were guns everywhere,” said environmentalist Drew Harvell The AtlanticEd Yong last year. “It looked like an explosive area.”
The sad remains of these animals, which are often able to regenerate their own limbs, spread across the west coast of North America, in one of the largest wildlife mortality events ever recorded. More than 20 species of starfish died.
In some areas, the sunflower star (Pycnopodia helianthoides) populations fell by about 90% on average in weeks, a loss that wiped out this once common and abundant species from most of its area in a few years.
The culprit that caused this starfish (SSW) waste even reached starfish in captivity and killed individual animals in a matter of days.
Bed of Pisaster ochraceus disintegrating from starfish destruction syndrome. (Elizabeth Cerny-Chipman / Oregon State University / CC BY-SA 2.0)
This led scientists to suspect that some kind of pathogen, such as a virus or a bacterium, was infecting these impressive sea creatures. However, later studies exonerated the suspect from the main virus.
Meanwhile, more starfish deaths occurred worldwide, including half the world in Port Phillip Bay, Australia.
Now, San Francisco State University marine biologist Citlalli Aquino and colleagues have finally unraveled the mystery, showing that something much more complicated was happening.
By comparing the types of bacteria within healthy starfish and those suffering from wasting disease, the researchers found that bacteria that thrive in low-oxygen environments were abundant in diseased animals, as were copiotrophs, bacteria that they like environments with high nutrients.
Experiments back in the lab confirmed that depletion of oxygen water caused tissue fusion injuries in 75 percent of starfish. The addition of excess nutrients or phytoplankton to the water also caused the starfish’s health to decline.
By re-analyzing tissue samples from the 2013 event, the researchers detected excess nitrogen, a sign that these animals suffocated to death.
“Starfish diffuse oxygen through its outer surface through small structures called papules or gills in the skin,” said Ian Hewson, a marine microbiologist at Cornell University. “If there isn’t enough oxygen around the papules, the starfish can’t breathe.”
These microorganisms do not directly cause disease, but steal the oxygen supply from starfish when increased levels of organic matter are causing microbes to bloom. As a result, starfish literally drown in their own environment. Then their decaying bodies further increase nutrients for microbes, creating a horrible feedback loop of starfish death.
Aquino and the team noted that most SSW events occur in late fall or summer, when phytoplankton that increase nutrient levels in water through photosynthesis are more abundant.
Warmer temperatures are the known engines of phytoplankton flowering, and the starfish wastage event in Australia followed the longest, most intense heat wave on record. Sea star wastage events elsewhere have also followed rising sea temperatures.
“Warmer waters can’t have as much oxygen [compared with colder water] just for physics, “Hewson told Erin Garcia of Jesus in Scientific news.
None of this augurs our future on a warming planet.
University of Vermont biologist Melissa Pespeni, who did not participate in the study, said Scientific news this complicated mess of biological and environmental factors is “a new kind of idea for [disease] transmission. “
The devastating repercussions of the loss of these precious starfish have already resonated in entire ecosystems. The sunflower star is a voracious predator with up to 24 arms spanning up to 1 meter (3.3 feet), making its way across the seabed to hedgehog hedgehogs, snails and other invertebrates.
Without the sunflower and other starfish keeping sea urchins under control, these herbivores are being eaten through giant algae forests. By 2016, sea urchins had already reduced algae populations by 80 percent in some areas, and demarcated these once-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 total reminder that everything is connected to everything else.”
This research was published in Frontiers in Microbiologyi.