Diamondback Terrapin

Overview

The Diamondback Terrapin (Malaclemys terrapin) is an exquisite, medium-sized estuarine turtle that holds a completely unique ecological distinction: it is the only turtle species in North America that lives exclusively in the brackish waters of coastal salt marshes, tidal estuaries, and mangrove lagoons. Celebrated as the official state reptile of Maryland and the beloved mascot of the University of Maryland, this handsome reptile is instantly recognized by the magnificent, concentric raised rings and ridges on its top shell (carapace) that resemble sculpted diamond facets, paired with pale gray to white skin speckled with intricate black spots and spots.

Holding an irreplaceable niche as a keystone predator in coastal marsh ecosystems, Malaclemys terrapin feeds voraciously on marsh periwinkle snails (Littoraria irrorata). By regulating snail populations, terrapins prevent the snails from overgrazing and destroying coastal cordgrass (Spartina alterniflora) beds that protect shorelines from hurricane storm surges. Historically prized as an extravagant culinary delicacy during the late nineteenth and early twentieth centuries—when millions were harvested for gourmet turtle soup in luxury dining halls—the diamondback terrapin is now the focus of intense coastal conservation.

Biology and Physical Characteristics

The physiological adaptations of Malaclemys terrapin to life in fluctuating salinity are an evolutionary triumph. To survive in salty estuarine water, the terrapin possesses specialized salt-excreting lachrymal glands behind its eyes that pump excess sodium chloride out of its bloodstream in salty tears. Its skin is exceptionally impermeable to salt ions, and it drinks freshwater from the surface lens that forms atop marshes during rainstorms. Its skull features massive, broad crushing jaw surfaces (crushing alveolar plates) lined with tough keratin that effortlessly shatter the thick calcified shells of periwinkle snails, ribbed mussels, and crabs.

Behavior and Ecology

Diamondback terrapins are diurnal and strongly tied to tidal cycles, moving up into flooded cordgrass marshes on rising tides to hunt grazing snails and retreating into deep tidal creeks during low tide to avoid desiccation. In winter, they bury themselves in the muddy beds of tidal creeks to brumate. In late spring, mature females crawl out of the marsh onto adjacent sandy dunes, coastal barrier beaches, and road shoulders to excavate flask-shaped nests, depositing 8 to 18 pinkish-white eggs that hatch after 60 to 80 days.

Conservation and Human Impact

Malaclemys terrapin is classified as Vulnerable on the IUCN Red List. Decimated historically by the commercial soup trade, its primary contemporary threats include drowning as bycatch in commercial and recreational wire blue crab traps, road mortality of nesting females crossing coastal causeways, and shoreline bulkheading that destroys sandy nesting beaches. Mandated Bycatch Reduction Devices (BRDs)—simple plastic excluder rings installed in crab traps—allow crabs to enter while preventing terrapins from drowning.

Interesting Factoid

The diamondback terrapin is the only turtle in North America that lives exclusively in salty coastal marshes, and its jaw is so incredibly powerful that it crushes hard clam and snail shells with a loud crunching sound audible to boaters yards away.