Cyanobacteria, also known as blue-green algae, are single-celled organisms that are naturally found in all types of water. These organisms are similar to plants in the way they rely on sunlight for survival. In relatively small numbers, these organisms are completely harmless. However, when circumstances are right, these cyanobacteria can reproduce rapidly, causing what's known as an algae bloom. Due to modern advancements in agricultural fertilizers and irrigation systems, these blooms are becoming more and more frequent and are to blame for many ecological disasters around the world.
One example of the damage caused by these algae blooms in Lake Okeechobee in Florida. This lake is the third-largest lake in all of the United States and attracts bass fishermen from all over the world. Recently this world-famous bass, along with all other inhabitants of the lake has been dying in huge numbers. This is due to the catastrophic algal blooms that occur annually in this lake. Surrounding Lake Okeechobee is a large number of ranches and farms that use fertilizers with a high concentration of phosphorus. When it rains, as it does a lot in Florida all of these fertilizers get washed away through the soil and inevitably into the Lake. These fertilizers, while great for making crops grow, are absolutely amazing at causing the Cyanobacteria population to grow exponentially. This influx in fertilizer is then paired with the massive amount of sunlight the lake receives all year round to create the perfect environment for this bloom to keep growing. This bloom is alarmingly effective in destroying all underwater life and a lot of terrestrial life through it's two devastating techniques. One of its techniques is fairly straightforward: The cyanobacteria produce one of the most powerful and harmful natural poisons in the world. This toxin can affect humans, dogs, and any other animal that may come in contact with the water. Currently, there are no known remedies for this toxin. The blue-green algae then destroy all underwater life by naturally forming a film across the surface of the water that blocks sunlight from reaching the underwater plants below and consumes a vast amount of oxygen. These underwater plants, which are the main oxygen source for the lake, then die, thus meaning not nearly as much oxygen is being produced in the water. Not only this but the dead plants then get decomposed by bacteria in the water, thus raising the oxygen demand in the lake. With no oxygen producers left to meet this demand, all life forms in the water such as fish that rely on oxygen to survive, die. This process is known as anthropogenic eutrophication.
Another example of the danger of cyanobacteria comes from the other side of the world, Botswana. As of July 14th this year a total of 280 elephants suddenly died in the span of a couple of months. These elephants were seen to walk in circles and appear dizzy before falling face-first into the ground. The cause of death was a mystery to scientists up until the 11th of October when the Botswana Government confirmed, through tests of the elephant carcasses, that it was in fact due to the toxin produced by cyanobacteria. According to an article written in Interdisciplinary Toxicology, cyanotoxin is produced due to cyanobacteria's ability to form a variety of secondary metabolites, some of which are potent toxins. According to Wiegand and Pflugmacher, these toxins can be categorized as hepatotoxins, neurotoxins, cytotoxins, dermato toxins, and irritant toxins (2005).
With the dangers of this bacteria in mind, it is sad to think that humans are the cause of their mass reproduction. The Florida state government announced in 2001 that they would reduce the amount of phosphorus entering Lake Okeechobee by 70% by 2015. Now in 2020, there is no appreciable change. This means it is up to us, the consumer, to help fight this battle, not only for Okeechobee or Botswana but for ecosystems around the world. If we make the choice to consume organic produce that doesn't use phosphorus heavy chemical fertilizers, producers will be forced to alter their production methods to ones that use organic fertilizers. Us consumers hold complete power over the outcome of this and our preferences are what producers need to meet, it's in our hands. Not only this but you can help raise awareness of this issue by talking about it with friends and family.
Wiegand C, Pflugmacher S. Ecotoxicological effects of selected cyanobacterial secondary metabolites a short review. Toxicology and Applied Pharmacology. 2005;203:201–218.