Florida Dolphins Show Alzheimer’s-like Brain Changes Linked to Algal Bloom Toxins

A new study published in Nature Communications Biology reports that bottlenose dolphins from Florida's Indian River Lagoon are exhibiting brain chemistry and tissue changes strikingly similar to early-stage Alzheimer’s disease in humans. Researchers say the findings do not indicate an immediate human health emergency but underscore an urgent need to investigate harmful algal bloom (HAB) neurotoxins as a potential environmental threat to both marine life and people.

What researchers found

During algal bloom seasons, stranded dolphins were found to have roughly 2,900 times more algal neurotoxin in their brains than dolphins stranded outside bloom periods. Scientists believe the primary exposure route is through fish that feed in contaminated waters, though toxins can also become aerosolized at the water’s surface and be inhaled by dolphins and other animals.

In toxin-exposed dolphins, researchers observed hallmark changes that mirror early Alzheimer’s disease: abnormal accumulation of proteins in the brain and altered expression of genes associated with memory and neural health. The study is among the first to directly link HAB neurotoxins with Alzheimer’s-like brain pathology in a wild marine mammal.

Ecological and climate context

Declines in seagrass in the lagoon have forced dolphins to shift their diets toward different fish species, which may increase their intake of contaminated prey. Researchers also note that repeated or long-term immune stress could make dolphins more vulnerable to neurological damage from toxin exposure.

Harmful algal blooms occur when certain microscopic algae multiply rapidly and, in some cases, produce cyanotoxins or phycotoxins. Blooms are fueled by excess nutrients such as nitrogen and phosphorus from fertilizer, sewage or storm runoff, and are favored by warm, shallow, sunlit, and calm waters. Climate change — including warmer temperatures and heavier rainfall — can increase the frequency and intensity of blooms.

Risks to animals and people

Not all algae produce toxins, but when they do, animals and humans who drink, swim in, or inhale contaminated water or aerosols can be affected. Pets are especially vulnerable because toxins can cling to fur or paws and be ingested when animals groom themselves. Reported symptoms in animals include vomiting, diarrhea, weakness, tremors, seizures and, in severe cases, breathing difficulty or death.

What’s next

Researchers recommend expanded monitoring of algal blooms, wildlife health, and potential human exposure, along with targeted studies to identify which toxins and exposure pathways are responsible for the observed brain changes. Continued investigation will help determine whether environmental neurotoxins contribute to neurodegenerative processes across species and inform strategies to protect both marine ecosystems and public health.