A month after Hurricane Ian, southwestern Florida is experiencing harmful algae blooms. The hurricane stirred up sediment in the Gulf of Mexico. This led to bright green and blue clouds of algae on the coast that can be seen in satellite images.
The algae bloom is the result of Karenia brevis, which causes the deadly red tides in the Gulf of Mexico. The Florida Fish and Wildlife Conservation Commission detected these microscopic algae in large quantities in samples taken from the Gulf. Scientists took samples off the shores of Sarasota, Charlotte, Lee, and Collier counties.
The FWC took 57 samples from the Gulf. It reported that 18 samples contained harmful bloom concentrations. According to archived data from the FWC, the algae was at very low concentrations all throughout September. But, Hurricane Ian stirred up the algae and sediment and created a larger concentration.
Tracy Fanara, a hydrologist with Mote Marine Laboratory in Sarasota County, theorized that the hurricane contributed to the appearance of the blooms. But, she clarified, the link between red tide and hurricanes is indirect at best. Red tide is more caused by ocean physics and chemistry changes caused by hurricanes rather than the storms themselves.
“We’ve seen hurricanes indirectly initiate blooms and we’ve seen them dissipate blooms, and we’ve seen them not have an impact at all,” Fanara told AccuWeather. “Water movement offshore of Tampa Bay during Hurricane Ian looked very similar to Hurricane Irma, which also inspired upwelling followed by [the] indication of a Karenia brevis bloom in the following weeks.”
Florida Experiences Harmful Algae Blooms Following Hurricane Ian
According to a report from AccuWeather, there was an algae bloom that lasted for two years following Hurricane Irma in 2017. It was exacerbated by heavy storms in 2018, as well. Lake Okeechobee overflowed, releasing toxic freshwater algae. This drained into the existing red tide bloom, containing nutrient-rich run-off which fed the bloom.
Currently, the theory about red tide blooms is that they develop offshore at the bottom of the ocean. They then move toward the shore with currents or upwelling, which is any event that raises seawater. For example, hurricane winds disrupt surface water, which brings nutrient-rich water and sediment to the top.
It’s that nutrient-rich water that feeds a harmful algal bloom. Storms wash away fertilizer, herbicides, and wastewater overflow, according to AccuWeather, which causes the blooms to grow and last longer than they should.
After Hurricane Ian, though, the runoff could be seen from space. Satellite images from the NOAA garnered attention, as they showed thick clouds of light blue water seeping into the Gulf. That indicated that sediment was washing into the ocean, feeding the algae and bacteria off the coast.
Red tide can cause respiratory problems the longer it sticks around. A few cases were already reported in Sarasota County. There’s no surefire way to predict how long the bloom will last. But, it does depend on how long the favorable conditions last. Scientists are looking at ocean physics–currents, salinity, and water temperature–the availability and amount of nutrients in the water, and the phytoplankton community offshore.