Spend a day walking along the seashore and you might see a disturbing sight: a stranded dolphin or a whale stuck on the sand. If you find a living animal, there is still a chance to save it – that is, if you contact the relevant authorities in time. But if you notice an already dead marine mammal, then nothing can be done: the animal died in the sea or on the shore, abandoned by the waves.
The scene is sad, whatever the circumstances, but why do such clashes happen in the first place?
A team of biologists decided to answer this question in a study conducted in Communication biology. By looking at the brains of stranded dolphins, the team found that the animals showed signs of illness similar to those seen in people with dementia, suggesting that brain deterioration similar to Alzheimer's disease may be contributing to the dolphins' time in the sand. The team notes that this brain damage, which is potentially exacerbated by toxic cyanobacteria, could worsen as well as algal blooms, including due to climate change.
Read more: The unique relationship between whales and dolphins
Do marine mammals come ashore?
According to the agency, thousands of stranded marine animals are reported to authorities every year. National Oceanic and Atmospheric Administration (NOAA). Although some strandings result in rescue operations involving professional rescuers (such as NOAA) relocation partners) evaluate and stabilize the animal before releasing it or returning it to a rehabilitation center, many of which end in death when the stranded animal dehydrates or—in the case of dolphins or whales—drowns.
But despite the prevalence of strandings among dolphins and whales, scientists are still not sure why these marine mammals strand themselves. To solve this problem, the biologists who conducted the study analyzed the brains of 20 deceased bottlenose dolphins.Tursiopes are truncated Truncated) which washed ashore in Florida between 2010 and 2019.
Their analysis showed that the dolphins' brains showed signs of dementia. And not only that; it also demonstrated that the brains of some dolphins contain elevated concentrations of certain toxins, such as 2,4-DAB, a substance that has been reported some research – may contribute to brain deterioration similar to Alzheimer's disease. Taken together, the results suggest that stranded dolphins may have become entangled in the coastal area before they beached themselves, just as dementia patients become disoriented in their surroundings due to something similar to Alzheimer's disease.
Read more: Dolphins and whales apparently sleep with one eye open
Algae bloom threat
But where do the toxins in some dolphins' brains come from? According to the team, algal blooms are a potential source since 2,4-DAB is a product of cyanobacteria. Indeed, the team found about 2,900 times more 2,4-DAB in the brains of dolphins that stranded during the algal bloom season than in the brains of those that stranded outside of the season. So it's possible, the team adds, that the brain damage and disorientation of these dolphins was exacerbated (as some dolphins' brains degrade as they age on their own) by something as benign as cyanobacteria.
“Although there are likely multiple pathways to Alzheimer's disease, exposure to cyanobacteria is increasingly emerging as a risk factor,” said David Davis, study author at the University of Miami Miller School of Medicine, according to the study. statement. “Because dolphins are considered ecological guardians of toxic exposures in the marine environment,” Davis added, “there are concerns about human health issues associated with cyanobacterial blooms.”
The team states that some research show that concentrations of certain cyanobacteria blooms also increase people's chances of developing degenerative diseases, meaning that the threat to dolphins is also a threat to humans.
While more research could provide clarity on the cause of these strandings, as well as the role of dementia and cyanobacteria in them, the results seem to highlight that algae blooms are best avoided for both dolphins and humans.
Read more: How smart are dolphins?
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