Rare rust tide bloom near Sanibel raises concern for marine life

Bernie Montás of Gulf Coast News reports that researchers have identified a rare rust tide bloom in waters near Sanibel.

WINK News reporter Riley Lehman separately reports that the organism, Margalefidinium polykrikoides, has been observed since September 1 around Sanibel, Tarpon Bay, Captiva Pass, Pine Island Sound and Cayo Costa.

WINK says this is only the second time the organism has been detected in the area since 2023.

Why researchers are concerned

Rick Bartleson of the Sanibel-Captiva Conservation Foundation told Gulf Coast News that the bloom removes oxygen from the water. That can harm marine animals and plants, especially organisms that cannot move to water with more oxygen.

Jason Pim of Calusa Waterkeeper told the outlet that rust tide does not have the same airborne human effects as red tide. He advised people to avoid water that shows visible signs of an algae bloom while researchers continue monitoring it.

The outlets report that only limited fish deaths had been observed as of Tuesday night. Researchers said the bloom could cause more if high concentrations persist.

No public sample bulletin was available

No public agency or laboratory bulletin documenting this rust tide bloom was available for this desk to inspect. The latest public weekly updates from the Sanibel-Captiva Conservation Foundation and the Florida Fish and Wildlife Conservation Commission predate the outlet reports and do not document this organism near Sanibel.

This brief therefore relies on the named researchers' on-record assessments carried by Gulf Coast News and WINK News. It does not treat red tide data as a record of the separate rust tide bloom.