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Marine Lab plans seagrass surveys to support manatee zone

By Staff | Jun 3, 2020


Those familiar with the waters on the east side of Sanibel know that slow speed zone buoys once marked a 300-foot-wide zone from the Lighthouse to Dixie Beach Blvd.

Recently, the zone was determined by state officials to be inconsistent with the existing rules governing slow speed zones. However, the 300-foot-wide buffer is used by manatees and the leading cause of death for manatees is boat strikes.

The SCCF Marine Lab has planned a seagrass survey to provide more information about manatee habitat to existing maps of manatee use of the zone. A report will be provided to support an ordinance by the city of Sanibel to designate it as a manatee protection zone, which will require boats to operate at slow speeds.

Seagrass is the primary food source for manatees.

“They are increasingly relying on the lower estuary because of warmer water temperatures in the winter,” Marine Lab Director Dr. Eric Milbrandt said. “While most seagrass areas are mapped using airplanes, aerial photos from sources such as Google Earth, and then interpreting seagrass presence or absence, there is very little ground truthing of the boundaries or the condition of the seagrass around Sanibel.”


There are 10 transects, which are indicated by the red lines in the map.

“We will randomly sample along the transect to measure seagrass species composition, shoot density per square meter, canopy height, and observe any macroalgae presence,” Milbrandt said.

In coordination with the city, the findings will be used along with existing manatee surveys and mortality data to support the designation of the area as a manatee protection zone.