Dolphins may be getting an Alzheimer’s-like disease due to this neurotoxin

For marine biologists, dolphins are often viewed as sentinel species, or animals that shed light on the health of the ocean. Along with whales, porpoises, and other cetacean species, dolphins are one way that researchers know to sound the alarm about environmental hazards that might affect the ocean as a whole and potentially humans. 

In this context, researchers have connected neurotoxins from algal blooms to brain changes associated with an Alzheimer’s-like disease in dolphins in Florida. This connection does not bode well for human communities exposed to those same substances. 

“These results are concerning because dolphins share coastal waters with humans and face many of the same environmental risks we do,” Wendy Noke Durden, a researcher at Hubbs-SeaWorld Research Institute’s Florida Laboratory, said in a statement emailed to Popular Science. 

Algae are tiny, photosynthetic organisms that live in natural bodies of water and an algal bloom takes place when an algae density rapidly increases. Some types of algae produce poisonous substances called toxins. Among these, neurotoxins specifically impact the body’s nervous system. 

[ Related: A lone dolphin has been yelling into Baltic Sea for years. ]

In a study published in the journal Communications Biology, Durden and her coworkers show that dolphins found beached during an algal bloom in the Indian River Lagoon along Florida’s Atlantic Coast had an alarming amount of a neurotoxin called 2,4-diaminobutyric acid (2,4-DAB) in their brain.University of Miami neurotoxicologist and study co-author David Davis tells Popular Science that 2,4-DAB has a similar chemical structure to BMAA, a cyanobacterial neurotoxin associated with neurodegeneration. It’s also important to note that while cyanobacteria are frequently called “blue-green algae,” they aren’t actually algae. Davis says that harmful algal bloom is a blanket term that includes different species.

The dolphins who stranded during the summer algal bloom season had 2,900 times the concentration of 2,4-DAB than those from non-bloom seasons. Those with a higher concentration of this neurotoxin also had more severe changes in their brain chemistry and tissue that are associated with early Alzheimer’s disease. These include an unusual build-up of insoluble proteins and alterations in important genes linked to memory, brain health, and Alzheimer’s disease risk. What’s more, these results were consistent across dolphin strandings for close to a decade, and the changes were more drastic with each algal bloom season.

Given dolphins’ identity as a sentinel species, “there are concerns about human health issues associated with cyanobacterial blooms,” Davis explained. “Although there are likely many paths to Alzheimer’s disease, cyanobacterial exposures increasingly appear to be a risk factor.” 

What’s more, a warming climate, nutrient pollution, and sewage will continue to intensify such harmful algal blooms, he adds. As such, there needs to be more research into the consequences of harmful algal blooms and exposure to their toxins.