Aerial photos show sprawling algal blooms. What causes them in Florida?

Archive photos show a sea of green in Florida. What usually causes harmful algal blooms along the Sunshine State’s coasts?

Harmful algal blooms — out-of-control colonies of microscopic algae — are a “growing problem” in every “U.S. coastal and Great Lakes state,” according to the National Oceanic and Atmospheric Administration.

They affect the “health of people and marine ecosystems,” and can also have a detrimental effect on the economy, according to NOAA, especially in coastal communities that are particularly dependent on fishing and tourism.

Climate change, along with increases in nutrient pollution, could cause harmful algal blooms (HABs) to occur more frequently, according to the agency.

Harmful algal blooms can “produce toxic or harmful effects on people, fish, shellfish, marine mammals and birds,” NOAA’s website states. Human illnesses caused by HABs are rare, but they can be “debilitating or even fatal.”

Sea of green? Aerial photos show toxic algae blooms, including in Florida waters

What are harmful algal blooms composed of?

Harmful algal blooms can be caused by a range of organisms, NOAA states, including “toxic and noxious phytoplankton, cyanobacteria, benthic algae, and macroalgae.”

Some HABs can make wildlife-killing toxins that negatively affect fish, mammals and birds, and can also cause human sickness or death in “extreme cases.” Other blooms, while nontoxic, can consume “all of the oxygen in the water as they decay, clog the gills of fish and invertebrates, or smother corals and submerged aquatic vegetation.” Additionally, some algae can discolor water, pile up on beaches or contaminate drinking water.

What usually causes harmful algal blooms along Florida’s coasts?

In the Gulf of Mexico, especially along the west coast of Florida, HABs are most often caused by Karenia brevis, which can turn the surface of the ocean a deep red.

Although there’s no way to predict exactly when a Karenia brevis overgrowth might occur, scientists can forecast the movement of a “red tide” when it does crop up by using wind and water data, according to the Florida Fish and Wildlife Conservation Commission.

They can last “as little as a few weeks or longer than a year,” and how long a bloom persists in “nearshore Florida waters” depends on a variety of factors, including nutrients, salinity and sunlight, reads the FWC’s website.

Sarah Perkel is a South Florida Connect Reporter for the USA TODAY Network’s Florida Connect team. You can get all of Florida’s best content directly in your inbox each weekday day by signing up for the free newsletter, Florida TODAY.