For decades, marine biologists have been puzzled by why dolphins and whales strand themselves on beaches. A new study suggests that dolphins may experience Alzheimer's-like brain degeneration due to exposure to harmful cyanobacterial toxins, compounds increasingly present in warming, nutrient-rich waters.

Toxic Blooms in the Ocean

Cyanobacteria, microscopic organisms that thrive in warm waters enriched with nutrients from agricultural runoff and sewage, produce neurotoxic compounds such as β-N-methylamino-L-alanine (BMAA), 2,4-Diaminobutyric acid (2,4-DAB), and N-2-aminoethylglycine (AEG). Once released into marine ecosystems, these toxins accumulate in food chains, reaching apex predators like dolphins.

Similar toxins have been linked to Alzheimer's-like pathology in humans, particularly among residents of Guam who consumed cyanobacteria-contaminated foods. These compounds can trigger misfolded tau proteins, amyloid plaques, and other neurological damage.

Evidence from Stranded Dolphins

Researchers examined the brains of 20 bottlenose dolphins stranded along Florida's Indian River Lagoon. Dolphins that stranded during peak cyanobacterial blooms had up to 2,900 times more 2,4-DAB in their brains compared with dolphins stranded at other times. Examination revealed hallmark features of Alzheimer's disease, including β-amyloid plaques, hyperphosphorylated tau proteins, and TDP-43 protein inclusions, along with 536 genes expressed in patterns consistent with human neurodegeneration.

Climate Change and Human Impact

The study highlights the role of climate change and nutrient pollution in increasing the frequency and duration of cyanobacterial blooms. Water releases from Lake Okeechobee into the Indian River Lagoon exacerbate toxin levels, impacting both marine life and potentially human health. Dolphins, as environmental sentinels, provide early warning signs of risks posed by these toxins.

Dr. David Davis of the University of Miami Miller School of Medicine notes,“Since dolphins are considered environmental sentinels, these findings raise concerns about human exposure to cyanobacterial toxins.”

Implications for Conservation and Public Health

The research, published in Nature Communications Biology, was conducted by scientists from Hubbs-SeaWorld Research Institute, The Blue World Research Institute, University of Miami, and Brain Chemistry Labs. It emphasizes the urgent need to monitor and mitigate cyanobacterial blooms to protect marine mammals and human populations alike.

As oceans continue to warm and nutrient runoff increases, toxic blooms may pose a growing threat to marine ecosystems, dolphin cognition, and human neurological health.

MENAFN12102025007385015968ID1110183593