Ecology and Vulnerability

Northern Diamond-backed Terrapin

Background
The northern diamond-backed terrapin is a medium-sized turtle that lives in brackish water habitats such as bays, sounds and estuaries. This subspecies of the diamond-backed terrapin typically inhabits coastal salt marshes from New Jersey to Massachusetts, which is the northernmost edge of its historical range ¹. Other subspecies of the diamond-backed terrapin are found along the Atlantic coastline to as far south as Florida and Texas along the Gulf of Mexico. The northern diamond-backed terrapin has a wedge-shaped top shell with ring patterns and pronounced ridges along the top. Coloration is highly variable, with the shell usually being gray, light brown, green, and black, while the skin is usually grayish to black with spots and speckle patterns ⁷. Adult females are about twice the size of adult males ². Females become sexually mature at 8-10 years and males at 5-7 years ². They live to 40 years of age and possibly longer.

Northern diamond-backed terrapins hibernate during the winter months in mud by burrowing in creek beds or banks or in salt marshes. Nesting habitat primarily occurs in shrubland, dune, and mixed grassland habitats, as well as man-made trails on sandy beaches ⁴. They primarily feed on crustaceans such as small crabs, snails, and mollusks. Natural predators include raccoons, large crabs, fish, and seagulls. Raccoons in particular are known to be significant predators of terrapins, and can prey upon 90% of nests where they overlap in coastal habitats ⁴.

Recreational and commercial crab pots threaten terrapin populations by unintentional capture and drowning ⁵. Human development bordering coastal marshes and shorelines also have negative impacts, especially where terrapins occur in low numbers ¹¹. Roadside fences have been successful to prevent road mortality ⁹, but other coastal anthropogenically-engineered structures, such as bulkheads on beaches, prevent terrapin access to dune nesting habitat, which has energetic costs and alters their natural behavior ¹². Manmade structures constructed with gaps or other open features can provide terrapins better access to nesting habitat. Artificial nesting habitats can also be created to offset barriers to natural nesting areas ¹³.

Climate Impacts

Shifts in Range, Elevation, or Depth

Diamond-backed Terrapin (Malaclemys terrapin) may cause a 99.4% loss of current habitats and a decrease of 59.1% nesting area in New Jersey by 2100 (Ganter and Christman, 2023). In Maryland, Chesapeake Bay and other coastal areas are projected to lose 25-55% of Diamond-backed Terrapin habitat in the next 10 years and 80% by 2100 due to sea level rise (Woodland et al., 2017). 

Changes in Population

Rising temperatures may impact Diamond-backed Terrapin nest success; one study found that, at 34℃, hatching success decreased to 50% or less, with complete hatching failure at 37℃ (Rowe et al., 2020).
In Massachusetts, this species is at the northern edge of its range ¹⁰, which may increase its vulnerability to climate change. 

Increased erosion from sea level rise, storm surge, and human activities will likely alter this species’ habitat. Sea level rise, flooding, and storm surge events have a very high likelihood of disrupting nesting habitat and negatively influencing salt marsh food webs that support terrapin populations throughout their life cycles ⁸.

Because the sex of terrapins, as well as other turtles, is determined by temperature during incubation, increasing temperature due to climate change is likely to influence the ratio of males and females within their populations ³. These demographic changes may have serious impacts on terrapin responses and adaptation to future environmental change ⁶. Nonetheless, the mobility of this species as well as the diverse habitat conditions that terrapins can live in across their range may help this species cope with some of the impacts of climate change.