Kristen M. Hart and Carole C. McIvor
US Geological Survey, Center for Coastal and Watershed Studies, St. Petersburg, FL

Diamondback terrapins (Malaclemys terrapin) are long-lived turtles that exist as continuously distributed geographic populations along North America's Atlantic and Gulf coasts. Residing in salt marshes, mangroves, and tidal tributaries, the terrapin is the only North American turtle that lives exclusively in brackish water. One of the top predators of benthic macrofauna in the estuarine food chain, terrapins may play an important ecological role, and may thus be particularly suitable for monitoring as an indicator species.

Because the vital rates and population structure for terrapins are poorly understood, we initiated a mark-release-recapture (MRR) study in the Big Sable Creek (BSC) complex of Everglades National Park, Southwest FL. We collected data from 300 terrapins over 5 sampling occasions from November 2001 through October 2003 (29 sampling days) to estimate adult survival rate, capture probability, and abundance of mangrove terrapins. Additionally, we conducted noninvasive blood sampling of each individual for molecular genetic analysis. To determine the ecological and evolutionarily relevant management units for the species, we isolated microsatellite DNA from all blood samples to test the hypothesis that M. terrapin throughout their range comprise one single, homogeneous population. Furthermore we tested the hypothesis that male and female terrapins disperse equally.

We established the first adult survival rate ( = 0.79) and population estimate (mean N = 1545 individuals) for mangrove terrapins, and we determined that their distribution within Big Sable Creek lies largely in unsurveyed habitat in headwater streams. Terrapin captures often occurred in and around submerged algal-covered logs. Such habitat contains a diversity of algal species, and microhabitat structure (i.e., brush piles, peat slabs, etc.). These features may be important to consider when planning habitat restoration efforts for this and other coastal species of mangrove fauna.

Genetic analysis of 12 microsatellite markers in all turtles collected (N=1409 rangewide, N= 260 from 4 sites in south Florida) revealed a unique, multi-locus genotype for each individual. Overall, we found that that M. terrapin throughout their range exist as at least six distinct metapopulations or regional management units (MUs). These MUs do not coincide with previous morphologically-based subspecies designations. Within each MU, males act as dispersers of genetic material, facilitating gene flow among subpopulations. In Florida, terrapins from BSC are more similar genetically to other terrapins from Florida Bay, rather than to terrapins from St. Petersburg, FL. Our findings showed that Florida may have as many as 4 different MUs, which may pose a significant challenge for effective management strategies.

Contact Information: Kristen M. Hart, US Geological Survey, Center for Coastal and Watershed Studies, 600 Fourth Street South, St. Petersburg, FL 33701 USA, Phone: 727-803-8747 x3046, Fax: 727-803-2032, Email: kristen_hart@usgs.gov

(This abstract is from the 2006 Greater Everglades Ecosystem Restoration Conference.)

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