The northern diamondback terrapin is hands down one of the most unique creatures native to the United States. From its peculiar physical characteristics to its captivating habitat and evolutionary adaptations, the terrapin sets itself apart from its shelled cousins. Their permeable and soft skin, perfect for life in a wide spectrum of salinity in a brackish environment, varies from a broad range of blues and grays. Diamondback terrapins are ever-hungry carnivores, feeding on fish, crustaceans, and mollusks. They use their webbed feet and sharp nails to assist their strong head and jaw muscles to crush the shells of their prey. Terrapins have an internal mechanism that dictates seasonal behavior, such as courtship and nesting, feeding, fasting, and brumation. This also dictates daily behaviors like basking, drinking, hiding, and more. Since they inhabit brackish waterways and marshes, they are equipped with a salt gland that helps regulate the amount of salt in their bodies. They drink fresh rain at the surface of the water or in puddles to rehydrate, and also regulate hydration through eating habits. Since they strictly eat in water, when the body of water they are in is high in salinity, they ingest less food to prevent extra intake of salt through the ingestion of water. When the body of water they are in is low in salinity, they consume more because the risk of salt intake is much lower.
Malaclemys terrapin sport growth rings or annuli on their scutes, as a result from seasonal activity. They become very active in spring and summer causing an incline in growth. Once fall hits and winter approaches, they begin to fast and empty their stomaches. This prepares them for dormancy throughout the brumation period, slowing down growth. This contrast in activity from season to season creates these growth rings more prominent in youth rather than older specimens. As they age, the annuli begin to wear down and their shells become much smoother. They may live for as long as 25-40 years. Hatchlings have knobs located on the central keel of the carapace much like their cousins of the genus Graptemys, known as the American map turtles. Terrapins tend to lose the knobs with age, especially in the subspecies terrapin terrapin and centrata.
Once spring is in full swing, these semi-aquatic emydids (a family of turtles found in the western hemisphere made up of more than 50 species) begin to bask in the warm surface of the water, before moving to logs, rocks, or the swampy salt marsh banks. This is the time for courtship and mating. Males average 4-5 inches in carapace length where as females are 6-9 inches in carapace length. There have been reports of breeding aggregations from different subspecies in the northern populations as well as the southern populations, but little is known about mating behavior.
Once the brief period of mating is over, the females begin to develop eggs and seek suitable areas to nest. Gravid females venture onto land to find the perfect area in terms of substrate consistency, sunlight for heat, proximity to water and tidal fluctuation, as well as predation. They are very particular about where and when to dig their nests. As part of a survival instinct, terrapins are usually very secretive about nesting areas. With a constant awareness of potentially dehydrating and over heating, females will dig for anywhere from 10 minutes to an hour depending on substrate consistency, experience, and strength of nails and back legs. These flask shaped nests can hold a range of 6-15 elliptical eggs, respectively. Once she is done depositing her eggs, she heads back to the water to rehydrate and feed to regain her energy from this strenuous task. The leathery shelled eggs are incubated for a minimum of 45 days (but up to 70), with hatchlings emerging in late summer to early fall. Hatchlings will sometimes overwinter in the nest only to emerge in the following spring.
If the nest survives the incubation period without predation, hatchling diamondbacks use an egg tooth to tear the egg shell open and begin their struggle to dig out. Terrapin hatchlings will emerge in as many as 11 days apart from the same nest. It has been observed that hatchlings will sometimes pause after reaching the surface, eyes closed, eventually opening them while following the direction of the sun. It is believed that this could be a way for them to set their biological clock, or an internal solar acclimatization. They begin their journey to safety, usually in the roots and cover of vegetation first and foremost, ultimately making their way to the wrack zone (an area in the habitat displaying organic material left by high tide). This supplies them with excellent cover, an adequate food source, and hydration from tidal changes.
Predation, human encroachment, abandoned crab pots, and road mortality are huge factors in the decreasing numbers of these beautiful and important turtles. A study has shown only one in five terrapins will survive the journey from nest to marsh due to natural predation or overheating alone (Auger and Giovannone 1979). The charming Jersey Shore draws a large crowd in the summer months, the most active time for terrapins, making road mortality an inevitable threat. The sheer volume of roadkilled terrapins is astonishing. Researchers throughout the state have counted crushed terrapins in numbers up in the 1,000s on one road in a single season. These astounding creatures are a pivotal piece to our ecological puzzle. Slow down, be aware of their existence, and respect their role in these coastal habitats we share with them. For more information on how we are helping the Diamondback Terrapin, click here.