Microcystis aeruginosa, shown above, was the cyanobacteria responsible for the harmful algal boom that hit Florida last year. This species, which can make a liver damaging toxin, is one of the most common forms of cyanobacteria. Photo by Barry Rosen, USGS
USGS Press Release
May 31, 2017
A new U.S. Geological Survey study that looked at the extensive harmful algal bloom that plagued Florida last year found far more types of cyanobacteria present than previously known.
Twenty-eight species of cyanobacteria were identified in the extensive bloom, which occurred in the summer of 2016 in southern Florida’s Lake Okeechobee, the St. Lucie Canal and River, and the Caloosahatchee River. As the guacamole like sludge created by the bloom began to stick together, it formed a thick, floating mat that coated river and coastal waters and shorelines – affecting tourism, killing fish, and in some cases, making people sick.
The culprit causing the bloom was a well-known species of cyanobacteria called Microcystis aeruginosa. However, water samples collected by state and federal agencies before and during the disruptive bloom on Lake Okeechobee and the Okeechobee waterway were analyzed by the USGS and found to contain 27 other species of cyanobacteria.
Cyanobacteria, also known as blue-green algae, are naturally occurring microscopic organisms that, under the right conditions, can undergo explosive population growth, resulting in a harmful algal bloom.
While Microcystis aeruginosa was the most abundant cyanobacteria found, other species were present before, during and after last summer’s Florida bloom.
“It’s not just a single organism out there that has the potential to cause a Harmful Algal Bloom,” said Barry Rosen, USGS Biologist and lead author of the study. “There are a multitude of species, each with their own ability to create blooms, all of which can cause oxygen deprivation in water that can kill fish, and many with the ability to create toxins harmful to wildlife, or people.”
Hepatoxins formed by Microcystis aeruginosa are well known to have the potential to cause liver damage, but several other cyanobacteria present in this bloom can create equally or even more dangerous toxins. For instance, some of the cyanobacteria can produce cylindrospermopsin, which can damage the liver or kidneys, while other species produce neurotoxins, like anatoxin and saxitoxin. Saxitoxin is one of the most potent natural toxins in the world.
As bad as these four toxins can be, simple skin contact with them is normally not enough to cause harm to humans as they have to be ingested, but only a small amount is needed to jeopardize a person’s health.
“One of the main human risks with these toxins is if a drinking water treatment plant unknowingly pulls some of the bloom into their facility,” said Rosen. “If that happens, the water often isn’t treated properly and the toxins can make it into finished drinking water.”
This type of water contamination has become more common over the years and guidelines have been developed to help drinking water treatment plants mitigate possible drinking water contamination from toxic blooms.
Even though cyanobacteria are a natural and vital part of the food web, the extreme quantities found in a harmful algal bloom can cause negative effects on human health, aquatic ecosystems, and local economies.
The total economic impact of an algal bloom can be difficult to estimate, but according to the EPA, harmful algal blooms can influence property values, hamper commercial fishing, and slow down recreational business and tourism – which loses close to $1 billion each year across the United States due to blooms preventing fishing and boating activities.
“We have a good idea of the conditions which make a bloom more likely – warmer water, excess nutrients from runoff from homeowners’ yards or farmers’ fields when they fertilize, and slow moving water, to name a few,” said Rosen. “What we don’t understand is why under similar conditions sometimes we have a bloom, and sometimes we don’t.”
What triggers one species to bloom over another is also unknown.
“It is likely that no two blooms are exactly alike and there probably isn’t one single set of circumstances that can lead to a bloom.” Rosen said. “The complicated part scientists are dealing with is having dozens of different organisms with the potential to bloom, yet they all have their own specific parameters needed to make it just right for them.”
In time and with more knowledge on the factors that contribute to these blooms, scientists are hopeful they’ll be able to provide information that will help land managers reduce their occurrence, and potentially forecast when they’re going to happen.