It is well known that the blue-green algae blooms that frequently break out in Florida Bay can be deadly to sealife and harmful to the local sportfishing industry.
But an emerging body of science has also raised the specter that eating seafood from bloom-stricken waters increases one's chances of contracting ALS, also known as Lou Gehrig's Disease, as well as other neurological disorders.
"At this point, you don't want to run up the red flag, but you want people to be informed," said Deborah Mash, a professor of neurology at the University of Miami's Miller School of Medicine.
At the core of the emerging research is cyanobacteria, which because it photosynthesizes often in bodies of water is sometimes described as blue-green algae. The bacteria blooms when it is exposed to unusually high nutrient levels, which are often the result of fertilizer runoff.
But in the case of Florida Bay, the nutrients also come from decaying seagrass that has wilted under unusually salty water conditions. If you've even seen pond scum, you know what a bloom of cyanobacteria looks like.
Among the many toxins that cyanobacteria produces is one called BMAA (beta-N-methylamino-l-alanine). And that's where the plot thickens.
In the United States, 2.5 people per 100,000 develop ALS in a given year. A progressive degenerative disorder that affects nerves in the brain and spinal column, ALS causes those who suffer from it to lose control of all voluntary muscle movements. The disease ultimately robs people of their ability to speak and walk, and finally, to breathe on their own. ALS sufferers typically die from respiratory failure within five years.
ALS is the cause of approximately one out of every 350 deaths in the U.S., said Paul Cox, a botanist and biologist who is the founder of the Institute of EthnoMedicine in Jackson Hole, Wyo., which is searching for a cure for the disease.
But among the indigenous Chamorro people in post-World War II Guam, whose diets relied heavily on a fruit bat species that carry large amounts of BMAA due to their consumption of cyanobacteria-laden cycad seeds, scientists observed an ALS incidence of up to 100 times that much.
In a late 1990s study, Cox found high concentrations of BMAA in the brains of Chamorro who had died from ALS as well as in the brains of living Canadian sufferers of the neurological disorder Alzheimer's Disease. In contrast, the brains of Canadians who died of unrelated causes didn't have BMAA.
In the ensuing years, Cox has pursued his research in locales as far flung as western China, Japan, Peru and Qatar.
"We go to villages around the world where ALS rates are high and we find that their diets are very rich in BMAA," he said.
Studies conducted by other scientists have also suggested links between cyanobacteria, the BMAA it contains, and ALS.
For example, in a 2011 study, Dartmouth neurologist Elijah Stommel found that in northern New England people who lived within a half mile of bodies of water where blooms occur were 2.5 times as likely to suffer from ALS as those who do not.
Cox, however, is quick to point out that at this point linkage between BMAA and ALS is only a hypothesis.
"The evidence is very interesting, but the jury's still out," he said.
The jury, however, is not still out on the question of whether BMAA can work its way from cyanobacteria up the marine food chain.
In the waters off South Florida, mid-sized fish, crustaceans and even dolphins are documented carriers of the toxin. UM's Mash said she has also found BMAA in sharks, though she has yet to publish that data.
With its frequent cyanobacteria blooms, Florida Bay has proven to be an especially good study ground for scientists looking for BMAA in the aquatic food web.
In a 2010 paper that Mash co-authored with UM biologist Larry Brand and three other scientists, the research team found that Florida Bay pink shrimp were carrying as much BMAA as the fruit bats that the villagers in Guam were eating. The findings weren't uniform, though. Gray snapper carried very little of the toxin.
But the science wasn't only confined to Florida Bay. Brand took samples near south Biscayne Bay in the waning months of a blue-green algae bloom that affected the area between 2005 and 2007. The blue crabs there carried even more BMAA than the Florida Bay pink shrimp.
It's still not clear how much danger, if any, the consumption of local blue crab and shrimp poses.
Even if there proves to be a link between consuming BMAA-heavy food and Lou Gehrig's Disease, the threshold dividing a safe and dangerous level of consumption would have to be studied.
Scientists say genetics, too, would play a role. Just as some smokers are more likely than others to develop cancer, some individuals are more disposed to contract ALS.
Still, both Mash and Brand say they refrain from eating fresh catches from local waters.
"At this point, I would not eat any seafood out of Florida Bay or Biscayne Bay," Brand said. "But many people do. I'm just being overly cautious."