Florida on Alert: What Causes Harmful Seaweed Blooms?

The coast of Florida is under threat after scientists spotted more than 13 million tons of Sargassum, a yellowish-brown seaweed, drifting in the Atlantic Ocean last month — a record for the month of March says the New York Times.

On Tuesday Governor Ron DeSantis announced the award of more than $13.6 million for innovative technologies and short-term solutions to aid in the prevention, cleanup, and mitigation of harmful seaweed.

According to the National Ocean Service, harmful algal blooms (HABs) occur when colonies of algae—simple plants that live in the sea and freshwater—grow out of control while producing toxic or harmful effects on people, fish, shellfish, marine mammals, and birds.

While we know of many factors that may contribute to HABs, how these factors come together to create a “bloom” of algae is not well understood.

Studies indicate that many algal species flourish when wind and water currents are favorable.

In other cases, HABs may be linked to “overfeeding.” This occurs when nutrients (mainly phosphorus, nitrogen, and carbon) from sources such as lawns and farmlands flow downriver to the sea and build up at a rate that ‘overfeeds’ the algae that exist normally in the environment.

Some HABs have also been reported in the aftermath of natural phenomena like sluggish water circulation, unusually high water temperatures, and extreme weather events such as hurricanes, floods, and drought.

Seaweed blooms have negative effects on humans and fish

People often get sick by eating shellfish containing toxins produced by these algae. Airborne HAB toxins may also cause breathing problems and, in some cases, trigger asthma attacks in susceptible individuals, says the National Ocean Service.

When algal blooms block vital sunlight from reaching beneficial underwater plants that provide food and a place to live and grow for fish and other animals, the ecosystem can be negatively impacted. Algae become stressed and die when they deplete the nutrient supply or move from freshwater into saltier waters.

The decomposition of dying algae can reduce levels of dissolved oxygen in the water. Some fish species with little tolerance for low dissolved oxygen levels may die. In addition, some algal species can kill fish directly either by production of algal toxins or by clogging the gills.

As the seagrass washes ashore and begins to decompose, it degrades the water quality and pollutes beaches, scientists say. The decaying algae releases ammonia and hydrogen sulfide, which has an unpleasant odor like rotten eggs and can irritate the eyes, nose and throat.

For Florida the attack of harmful seaweed is nothing new. The coastal waters of Southwestern and Southeastern Florida were impacted by major blooms during the summer of 2016.