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.
CAMBRIDGE, MD — Hurricanes can stimulate toxic harmful algal blooms (HABs), according to a new study conducted by the University of Maryland Center for Environmental Science (UMCES) and published in Geophysical Research Letters. The connection, until now, has not been widely understood.
In September of 2022, Hurricane Ian, a Category-4 storm, pushed an excessive amount of nutrients inland, triggering a plethora of HABs. Over the next few weeks, a dangerous toxin-producing species, Karenia brevis, formed, lasting roughly six months.
K. brevis produces a potent neurotoxin, called brevetoxins, which can be found along the Atlantic coast and Gulf of Mexico, and is often to blame for Florida’s red tides. The presence of this organism can lead to fish kills, shellfish poisoning and, if inhaled in aerosolized form, respiratory problems in humans.
Scientists at UMCES created and utilized a unique model, allowing for a more comprehensive understanding of the ocean’s complex systems. Their research showed 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 offshore K. brevis cells toward the coast," said Ming Li, UMCES professor and primary investigator on the study. "A significant amount of nutrients remained after the initial diatom bloom, which was widely dispersed, creating prime growth conditions for K. brevis."
Florida Fish and Wildlife Research Institute (FWRI) and University of South Florida Red tide map, Oct. 24 - 30, 2022.
High winds and heavy precipitation in tropical storms are not unique to Florida and can affect plankton and HABs in other estuaries like the Chesapeake Bay and Pamlico Sound/the Neuse River.
"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," said Yuren Chen, UMCES graduate student and lead author on the paper. "Hurricanes discharge a large amount of nutrients into estuaries and coastal oceans, fueling phytoplankton blooms – in this paper, we have shown that hurricane-generated currents were capable of moving offshore HAB species towards the coast where they can make use of the nutrients discharged during the storms."
This study is timely as 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).
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