Gloeotrichia echinulata produces colonies that look like fuzzballs in the water to the naked eye. The colonies can move up and down in the water column to capture light and nutrients. It is not thought to commonly produce toxic blooms, but studies indicate it can produce toxins. (Photo by Mark Edlund)
The organisms known as blue-green algae aren’t actually algae. They aren’t even plants. They are a group of bacteria called Cyanobacteria who can convert energy from sunlight just like plants – a unique arrangement in the tree of life.
Cyanobacteria are notorious because they produce toxins that can sicken or kill pets and people. Every year in Minnesota humans fall sick and pets become seriously ill or die after swimming in or drinking water where these organisms are present. It’s called a bloom when Cyanobacteria start growing like crazy in a lake. The noxious bloom can block sunlight for other plants, outcompete other aquatic organisms, and degrade fish habitat.
Because Cyanobacteria are currently the most visible problem afflicting lakes in Minnesota and elsewhere, a lot of people are aware of the problem. But there is more than meets the eye when you see what looks like green paint spilled in a lake. Research Station scientists are studying these organisms as part of projects on Lake of the Woods and 10 other Minnesota lakes in collaboration with the Minnesota Pollution Control Agency and with funding from the Minnesota Environment & Natural Resources Trust Fund.
Cyanobacteria aren’t all bad though; fossil records point to them as the oldest group of organisms on the planet, meaning they were responsible for creating the first breath of oxygen on Earth.
This also means they have had a lot of time to evolve innovative ways of surviving and thriving:
1. 'Aquatic cockroaches'
A cyanobacterial bloom and a fishing bobber on St. James Lake in southern Minnesota. (Photo by Alaina Fedie)
Station scientist Adam Heathcote compared Cyanobacteria to the “cockroaches of aquatic systems,” because they can survive in almost any conditions found on Earth.
They are natural and normal parts of our ecosystem, with some form of Cyanobacteria found in almost every waterbody in the world – from Yellowstone’s hot springs to northern Minnesota’s clean and cold boreal lakes. Some even live on land, and are especially happy when it rains.
They aren’t always very noticeable. It’s only when massive blooms occur that we see them (and when their toxins reach dangerous levels). But they are always there.
2. Deep divers
One reason Cyanobacteria are so persistent is that they can move around in a lake to get what they need to grow. More accurately, they can move up and down in the lake.
Most algae prefer to be near the surface of a lake where light is abundant, but are at the mercy of wind and waves when competing with each other for limited nutrients.
But, by using special “ballast tanks” called aerotopes, Cyanobacteria can descend to the deeper waters of a lake to find rich supplies of iron and phosphorus and return to the surface to get the light they need to perform photosynthesis.
3. Fueled by nitrogen
The three clear cells seen in this sample of Dolichospermum crassum (formerly known as Anabaena) allow it to use atmospheric nitrogen. This species is also a known bloom former and can produce anatoxin, a potent neurotoxin, under certain conditions. (Photo by Mark Edlund)
Cyanobacteria are also different from algae because they can get their nutrients not just from the water, but from the air, allowing them to thrive during times of the year when dissolved nitrogen may be limited. This opens up a whole additional realm to fuel their growth. (Think Popeye and his spinach.)
Absorbing nitrogen gas is generally difficult for plants because oxygen is the “enemy” of the chemical process which converts it to usable forms. But Cyanobacteria have special structures (called heterocytes) with thick walls to keep the oxygen out where the nitrogen is converted to a form that can fuel growth.
4. Happy hibernators
The mass of larger bright green oval cells in the center of this sample of Dolichospermum are the akinetes that overwinter in the sediments. (Photo by Mark Edlund)
When winter comes, Cyanobacteria don’t just die off like most algae. It first forms a unique resting stage of the organisms (called an akinete), which sinks to the bottom of the water and waits until spring (and sun and nutrients) to return.
These types of Cyanobacteria reduce metabolism to almost nothing, and are protected by thick cell walls.
5. Strength in numbers
This photo shows three species of toxin-producing Cyanobacteria in a bloom, found in South Center Lake. The dominant species of Woronichinia naegeliana has slightly smaller cells in the colonies as compared to Microcystis aeruginosa which is also present in the sample (bottom center). The long filaments crossing through th center are a colony of Aphanizomenon flosaquae. (Photo by Adam Heathcote)
Because they can outcompete other algae for nitrogen and phosphorus, Cyanobacteria are able to reproduce rapidly under certain circumstances and create the giant blooms that turn a lake into pea-green soup. But take a closer look and the individual colonies of many Cyanobacteria are visible to the naked eye.
In a healthy ecosystem, when the number of algae increases, generally the number of zooplankton, which eat algae, also grows to compensate. That doesn’t happen with Cyanobacteria, which form colonies so large that zooplankton simply can’t eat them, or thy choke filter-feeding zooplankton with their long fibers, or can even poison them with their toxins. This lack of predatory “checks and balances” leads to the noxious, and sometimes harmful, bloom conditions for which Cyanobacteria are notorious.