Just off the sun-drenched coast of Florida, an unsettling mystery is unfolding beneath the waves. Bottlenose dolphins—those playful icons of marine life—are washing up dead, their brains riddled with toxins and the telltale scars of Alzheimer’s disease. According to recent research published in Communications Biology (October 13, 2025), these marine mammals may be warning us about invisible dangers lurking in our warming coastal waters. The findings are as fascinating as they are alarming, and they raise urgent questions about what’s happening to both dolphins and the millions of people who share their environment.
The story begins in Florida’s Indian River Lagoon, a sprawling estuary stretching along the state’s east coast. Between 2010 and 2019, researchers from Hubbs-SeaWorld Research Institute, the University of Miami, and Brain Chemistry Labs studied 20 bottlenose dolphins that had stranded along this 155-kilometer stretch. Every single dolphin tested positive for a brain toxin called 2,4-diaminobutyric acid (2,4-DAB)—a molecule produced by cyanobacteria during harmful algal blooms. The numbers were staggering: during the summer bloom months (June through November), toxin levels in dolphin brains soared to roughly 3,000 times higher than those found during the winter.
Why does this matter? Dolphins, as top predators and long-lived mammals, accumulate toxins in much the same way humans do—especially those who eat seafood. And when scientists examined the brains of these dolphins, they found something deeply troubling: the same genetic and physical hallmarks of Alzheimer’s disease seen in humans. Under the microscope, the dolphins’ brains revealed amyloid-beta plaques, tau tangles, and TDP-43 protein inclusions—hallmarks that pathologists recognize instantly in human Alzheimer’s patients. As KPVI reported, “Brain neuropathology similar to Alzheimer’s patients, including beta-amyloid plaques and hyperphosphorylated tau proteins, was found in the dolphin brains.”
According to Dr. David Davis of the University of Miami’s Miller School of Medicine, “Dolphins stranded during the summer cyanobacterial bloom season contained 2,900 times the concentration of 2,4-DAB than those from non-bloom seasons.” He further explained, “During bloom seasons, the same dolphins showed 536 differentially expressed genes associated with Alzheimer’s disease.” These genetic changes mirrored those seen in the brains of human dementia patients, including increased expression of three key Alzheimer’s genes: APP (amyloid precursor protein), MAPT (tau protein), and TARDBP (TDP-43 protein). In some dolphins, expression of the APOE gene—a major human Alzheimer’s risk factor—jumped up to 6.5-fold during bloom seasons.
But what’s behind these toxic blooms? Scientists point to a combination of climate change and nutrient pollution. Warmer ocean temperatures and runoff from agriculture and sewage have fueled longer-lasting, more intense blooms of cyanobacteria. As these microscopic organisms multiply, they release neurotoxins like 2,4-DAB, BMAA, and AEG into the water. These toxins climb up the food chain, concentrating in small fish and ultimately in the dolphins that eat them. The same process can occur in humans who consume seafood from affected waters.
“The duration of cyanobacterial blooms is increasing with climate warming and nutrient inputs associated with agricultural runoff and sewage discharges,” the study authors noted. And as KPVI highlighted, “Cyanobacterial-laden waters have often been released down the St. Lucie River from Lake Okeechobee into the Indian River Lagoon.”
The parallels to human health are hard to ignore. Miami-Dade County, just 200 miles south of the lagoon, recorded the highest prevalence of Alzheimer’s disease in the United States in 2024. While scientists caution that many factors contribute to dementia—including genetics, age, and healthcare access—the proximity of these outbreaks raises unsettling questions. Is it possible that chronic exposure to algal toxins in seafood or water could be increasing the risk of neurodegenerative disease in people living along Florida’s coast?
Dr. Davis voiced these concerns plainly: “Since dolphins are considered environmental sentinels for toxic exposures in marine environments, there are concerns about human health issues associated with cyanobacterial blooms.” His colleague, Dr. Paul Cox of Brain Chemistry Labs, pointed to studies of villagers on Guam, where chronic dietary exposure to cyanobacterial toxins was linked to neurological disease and Alzheimer’s-like brain changes. “Among Guam villagers, exposure to cyanobacterial toxins appeared to trigger neurological disease,” Cox explained.
The hypothesis is both novel and haunting: dolphins suffering from dementia may become disoriented, stranding themselves on beaches—much like humans with dementia sometimes wander far from home. As KPVI put it, “Researchers have been trying to work out why marine mammals become stranded on shore in the first place. A group of American scientists have come up with an unusual hypothesis: just as adult humans with dementia are sometimes found wandering far from their home, perhaps dolphins become similarly disoriented by suffering from a form of Alzheimer’s disease.”
The research team didn’t stop at observing physical changes. They dug deep into the dolphins’ genetic blueprints, uncovering 536 genes with significantly different expression levels between bloom and non-bloom seasons. Many of these genes overlapped with those disrupted in human Alzheimer’s disease. Notably, 15 genes showed expression patterns that correlated with both toxin concentration and the year of stranding, suggesting accumulating brain damage with each successive bloom season.
Some of the most striking changes were seen in genes related to the brain’s chemical balance and its protective blood-brain barrier. For instance, dolphins exposed to high toxin levels showed decreased activity in genes responsible for producing GABA, a neurotransmitter that calms brain activity. Meanwhile, genes related to the blood-brain barrier’s integrity were more active, possibly signaling that this crucial defense was under siege.
Of course, the study isn’t without limitations. The sample size was small—just 20 dolphins collected over nine years—and researchers couldn’t directly assess neurological function in living animals. The findings show strong correlations, not definitive proof of cause and effect. And while dolphins are considered sentinel species for environmental health, their biology isn’t identical to ours. More research is needed to determine whether similar mechanisms are at work in humans exposed to these toxins.
Still, the warning signs are hard to dismiss. Harmful algal blooms are on the rise worldwide, not just in Florida. From California to the Great Lakes, coastal communities are grappling with blooms that once were rare. Toxins can build up in fish, become airborne in sea spray, and persist in the environment for years. As climate change continues to warm our waters, the risks may only grow.
Sentinel species, like dolphins, exist for a reason. In the past, canaries warned miners of invisible dangers in the air. Today, dolphins accumulating brain toxins and developing Alzheimer’s signatures may be offering a similar alert for our coasts. The message from Florida’s waters is clear: as our climate warms and algal blooms intensify, we would do well to listen to the warnings coming from beneath the waves.
