What are Algae Blooms

Caloosahatchee Algae 062518 Alva Boat Ra

Florida is no stranger to a variety of algae blooms. You've probably heard of them.  Eye-burning red tide and Guacamole-textured blue-green cyanobacteria blooms. Blooms of the magnitude of any of these algae can lead to environmental, economic and public health problems. What causes these organisms to bloom by the masses? How much are humans to blame? How do we monitor and forecast these blooms?

Red Tide

What is it?

In Florida, red tide is caused by the accumulation of Karenia brevis, a type of single-celled organism called a dinoflagellate. They produce neurotoxins that can cause respiratory problems in humans and attack the central nervous system of fish and other wildlife. 

What does it look like?

Red tides are not always red. When blooms are in high enough concentrations, the water can appear red, brown, rusty orange or green. Sometimes, the hue of the water will remain normal, even during a bloom.

What causes it?

Red tide blooms in Florida begin 10-40 miles offshore in the bottom waters of the Gulf of Mexico, where K. brevis is almost always present at low and harmless concentrations. K brevis cells brought to the surface by a process in which deep, cold and nutrient-rich water rises to the surface.

Blue-Green Algae

What is it?

The most common kind of algae that produce blooms are blue-green algae, or cyanobacteria. These single-celled organisms use sunlight to make their own food and are found naturally in fresh, brackish and salt water. In warm waters that are high in nitrogen and phosphorous, cyanobacteria can multiply quickly, and spread across the water's surface.

What does it look like?

When cyanobacteria grow to excessive levels in Florida's freshwater bodies, the water can become stained bright green, sometimes forming thick scum on the water surface. This visibility of the bloom varies. Sometimes there may be a bloom that is not quite visible.

What causes it?

Blue-green algae need a few specific ingredients and conditions to grow:

* Nutrients, particularly nitrogen and phosphorous

* Sunlight

* Carbon dioxide

* Relatively calm water

* Heavy rainfall followed by drought

Nutrients, in particular nitrogen and phosphorous are critical to help build the algae's cellular mass. In the watershed north of Lake Okeechobee, it is estimated that the soils and wetlands contain enough nutrients from past agricultural activities to fuel high nitrogen and phosphorous inputs into Lake Okeechobee for the next fifty years, even if farming stopped today.

Sunlight and carbon dioxide from the water help fuel photosynthesis. And relatively calm conditions prevent algae from mixing too deeply into the water and being robbed of sunlight. In places with very shallow waters, calm conditions are not as critical because algae mixed to the bottom may still have enough light to fuel growth.

Red Tide and Blue-Green Algae 

UF Thompson Earth Systems Institute