Everybody knows about red tide, but rust tide? That’s a new one for most people. It recently showed up near Sanibel Island and Pine Island Sound in Lee County. This organism, scientists call it Margalefidinium, looks a lot like red tide. And just like its notorious cousin, it can wipe out entire schools of fish when it blooms.
Rust tide isn’t the same thing as red tide, though. While both turn the water murky and cause fish kills, rust tide doesn’t release airborne toxins. You won’t get itchy eyes or scratchy throats from it. People found it in several spots around Southwest Florida: Sanibel, Tarpon Bay, Captiva Pass, Pine Island Sound, and Cayo Costa. A volunteer pilot with Calusa Waterkeeper was the first to spot the bloom.
Bouts of rust tide are rare in Florida. The last bloom happened in 2023, but it’s common in places like Chesapeake Bay, where it shows up year after year and can stretch for miles. Researchers have also tracked it across Asia, Europe, and the Middle East.
The Sanibel-Captiva Conservation Foundation is on the case, monitoring this latest bloom. They know it matters because rust tide thrives in warm coastal water, and when it takes over, fish pay the price.
