Harmful algal blooms may be affecting dolphins’ brains and causing them to become disoriented and strand, according to researchers in the USA.
The scientists studied the brains of 20 bottlenose dolphins that had beached themselves along the Indian River Lagoon, on the east coast of Florida, and found a high level of neurotoxins related to harmful algal blooms (HABs). The findings are published in the journal Communications Biology.
As the climate gets hotter, blooms of algae called cyanobacteria are getting more frequent and intense. These microscopic organisms can produce harmful toxins, including β-N-methylamino-L-alanine (BMAA), 2,4-Diaminobutyric acid (2,4-DAB) and N-2-aminoethylglycine (AEG), which can damage nerve cells and cause Alzheimer’s-like disease.
“Toxins produced during HABs can bio-magnify in the aquatic food web, posing a significant health risk to marine life, terrestrial mammals, and humans,” says the study. “Several studies have shown neurotoxins originating from HABs to be concentrated in brain tissues of individuals diagnosed with neurodegenerative diseases.”
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When the scientists analysed the brains of 20 dolphins that had stranded between 2010 and 2019, they found that the neurotoxin 2,4-DAB was up to 2900 times more concentrated during periods of harmful algal blooms compared to times outside of HAB seasons. “2,4-DAB has been shown to provoke hyperirritability, tremors, and convulsions within hours of exposure,” says the study, although more research is needed to find out how it might be related to Alzheimer’s disease.
They researchers also found changes in the dolphins’ brains that resembled those related to Alzheimer's disease, and that these increased with each bloom season. If the dolphins were suffering from Alzheimer's-like symptoms and became disoriented, it might explain why they became stranded.
The discovery may also be cause for concern for humans as the toxins accumulate through the food chain and humans eating the seafood might be at risk. “Since dolphins are considered environmental sentinels for toxic exposures in marine environments, there are concerns about human health issues associated with cyanobacterial blooms," says Dr. David Davis at the Miller School of Medicine. "Although there are likely many paths to Alzheimer's disease, cyanobacterial exposures increasingly appear to be a risk factor.”
Warmer waters boost the chances of a harmful algal bloom occurring so the scientists highlight the importance of getting to the bottom of any links between HABs and health impacts.
“In 2024, surface temperatures on Earth were the warmest recorded in modern times. As global temperatures rise, HABs will continue to intensify, increasing the risk of exposure to algal toxins,” says the study. “Understanding the impact of HAB exposures will help to identify populations at risk for neurological illnesses.”