How was Charlotte Harbor formed?

By Betty Staugler, UF/IFAS Extension Charlotte County agent for the Florida Sea Grant Program

Have you ever wondered why there is less natural relief and hard bottom habitats in the Gulf off Charlotte Harbor compared to areas north and south? Well, somebody did, and they asked me. Not knowing the answer, I offered to do some research and write about my findings.

The first question I looked at: Is the habitat off Charlotte Harbor really different? That answer is, not surprisingly, yes. The FWC’s Fish & Wildlife Research Institute has been doing extensive side-scan mapping of the Gulf seafloor, and considerable data has been collected across the entire west Florida shelf (including off Charlotte Harbor) in water depths between 30 and 600 feet. The side-scan mapping provides a habitat component in support of reef fish surveys.

Because it’s not practical to side scan every inch of the west Florida shelf, the habitats mapped are randomly selected and then mapped along transect lines. Based on the mapping that has been done to date, the area off Charlotte Harbor likely wins for “most shelly sand.” In fact only about 3 percent of the substrate off Charlotte Harbor is anything other than shelly sand.

So back to the big question — why? The answer is not so simple. The type of geologic surveys that would be needed to answer this question have not been done for the area off Charlotte Harbor. What we know about the geology of the west Florida shelf for Southwest Florida is based on surveys off Tampa Bay and further south off Estero Bay.

But a very interesting paper sent to me by a geologist from the University of South Florida looked at the formation of Tampa Bay and Charlotte Harbor. This paper might be relevant, and since it’s pretty interesting, let me tell you about it.

Charlotte Harbor and Tampa Bay are big open-water estuaries. Big open-water estuarie