Nest microhabitat characterization and nest site selection by Mississippi diamondback terrapin (Malaclemys terrapin pileata) at Grand Bay National Estuarine Research Reserve (NERR), Mississippi

Diamondback terrapins (Malaclemys terrapin) are a small species of turtle endemic to Atlantic and Gulf coast salt marshes and are identified as a “Valued Ecosystem Component” in Grand Bay NERR's conceptual model. Maternal nest site selection is an important factor controlling offspring survival, fitness, and sex (via temperature dependent sex determination) because terrapins provide no parental care after eggs are laid. Annual (2007-09) surveys of terrapin nesting activity have been conducted along small, natural beaches located within the Grand Bay NERR. Nests depredated by raccoons (Procyon lotor) were used as a proxy for intact nests because freshly-laid nests are cryptic and difficult to locate. For each nest, the following data were recorded: GPS location, estimated number of eggshells, and percent cover of vegetation in a 0.25 m² and 1.0 m² area surrounding the nest. In addition, temperature loggers were deployed to record soil temperature at nest depth in vegetated and open beach areas. Each year, approximately 200 nest sites were identified during the nesting season (April-August). A significant number of nest sites were located in vegetated nesting beach areas versus open areas, results that differ from those observed in terrapin populations along the Atlantic coast. Saltmeadow cordgrass (Spartina patens) was the most frequently occurring plant species in vegetated nest sites. Average soil temperatures recorded in vegetated areas were lower and less variable than temperatures in areas of open sand. Additionally, temperatures causing anomalies and mortality occurred much less frequently in vegetated versus open areas (2008: 6% versus 30%). Terrapins utilize vegetated areas of nesting beach in order to better regulate nest temperatures and increase offspring survival. These results highlight important rangewide differences in terrapin life history and ecology, as well as the need for additional study of poorly known Gulf Coast terrapin populations.