The Sanibel-Captiva Conservation Foundation (SCCF) has revealed fascinating insights into the diamondback terrapins (Malaclemys terrapin), highlighting their unique adaptation to estuarine environments along the U.S. coast, from Massachusetts to Texas. These habitat specialists predominantly reside in salt marshes, with a significant portion in South Florida thriving in mangrove waterways.
“Throughout this expansive range, their appearance or phenotype changes depending on the region they occur in, even though they are all one species,” noted Chris Lechowicz, Wildlife & Habitat Management Director at SCCF. “These brackish water species can tolerate a wide variety of salinities, including hypersaline environments.”
Historically, diamondback terrapins have been classified into seven subspecies, each exhibiting distinct regional phenotypes. Florida is a biodiversity hotspot, hosting five of these subspecies, with three being endemic to the state.
In Lee County, terrapins are often identified as either ornate diamondback terrapins (M. t. macrospilota) or mangrove diamondback terrapins (M. t. rhizophorarum), depending on the source of the range maps.
“Since 2013, SCCF biologists have observed that most terrapins in the area resemble ornate diamondback terrapins,” Lechowicz explained. “However, a small yet consistent number of terrapins show characteristics more typical of the mangrove diamondback terrapin.”
The research highlights the occurrence of intergrades—terrapins with blended traits—at the intersection of the two subspecies’ ranges. Unlike hybrids, which result from the mixing of different species, intergrades occur within the same species.
Recent genetic studies by the Florida Fish and Wildlife Conservation Commission, incorporating samples from researchers statewide, aimed to verify if the phenotype-based subspecies range maps align with genetic data. The SCCF was a significant contributor to this study.
The findings adjusted the range of mangrove diamondback terrapins, extending it further up Florida’s west coast, slightly north of Sarasota. Consequently, based on genetic data, Sanibel is now recognized as home to mangrove diamondback terrapins.
“We discovered a variety of phenotypes within our population, some not closely matching either subspecies, while others fit one or both subspecies well,” Lechowicz added. “Island populations tend to resemble one subspecies more closely than mainland populations. We have shared recent photos showcasing the diversity in coloration and patterning in our area.”
The public is encouraged to report sightings and share photos of diamondback terrapins by emailing [email protected].
