March 26, 2025
The Sentinel-2 True Color Image taken on September 30, 2022, which shows nutrient-rich waters discharging onto the West Florida Shelf.
Hurricanes are one of the most powerful forces of nature, causing coastal flooding and, often, significant death and destruction to both our built and natural world. According to a recent study conducted by the University of Maryland Center for Environmental Science (UMCES), hurricanes can also stimulate toxic harmful algal blooms (HABs), which develop when algae grow in excessive levels.
In September of 2022, Hurricane Ian – the deadliest storm to hit Florida since 1935 – pushed an excessive amount of nutrients inland, triggering a plethora of HABs; in particular, a highly concerning toxicogenic species, Karenia brevis, which lasted for over six months.
In a new study published in Geophysical Research Letters, Ming Li, a professor at UMCES, and Yuren Chen, a graduate student, conducted a computational analysis by blending physical water processes with the chemical and biological processes of the ocean – utilizing the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system – allowing for a more comprehensive understanding of its complex systems and proving that Hurricane Ian drove the bloom in two ways.
"First, the northerly winds on the western half of Ian created a coastal upwelling of onshore bottom currents that transported subsurface K. brevis cells toward the coast," said Li. "A significant amount of nutrients remained after the initial diatom bloom, which were widely dispersed, creating prime growth conditions for K. brevis."
K. brevis produces a potent neurotoxin called brevetoxins, found along the Atlantic coast and Gulf of Mexico, and is often to blame for Florida’s red tides. The presence of this dinoflagellate can lead to fish kills, shellfish poisoning, and, if inhaled in aerosolized form, respiratory problems in humans.
Florida Fish and Wildlife Research Institute (FWRI) and University of South Florida Red tide map, Oct. 24 - 30, 2022.
Storms marked by high winds and heavy precipitation can push large amounts of nutrients inland, providing favorable conditions for K. brevis blooms. Moreover, this phenomenon is not unique to Florida.
"The same mechanism affects plankton and HABs in estuaries like the Chesapeake Bay and Pamlico Sound/the Neuse River," Chen said. "An example would be the large plankton bloom that developed after Tropical Storm Agnes in 1972, although it was not associated with an HAB species. Hurricanes discharge a large amount of nutrients into estuaries and coastal oceans, fueling phytoplankton blooms – in this paper, we have proven hurricane-generated currents moved them towards the coast."
Stronger and wetter tropical storms are expected to hit coastal regions more frequently in our changing climate.
Read the study in its entirety: Impact of Hurricane Ian (2022) on Karenia brevis Bloom on the West Florida Shelf (DOI: 10.1029/2024GL113500).
