Sea turtles are ancient, air-breathing marine reptiles that have navigated the world’s oceans for over 110 million years. These creatures are known for their extensive migrations, often traveling thousands of miles between foraging grounds and the beaches where they hatched. They play a foundational ecological role in maintaining the health of two distinct environments: the oceanic waters where they mature and the coastal beaches where they lay their eggs. By consuming invertebrates and transferring nutrients, sea turtles help shape the dynamics of coral reefs, seagrass beds, and dune systems.
Classification of Sea Turtles
The world’s sea turtles are grouped into the superfamily Chelonioidea, containing two distinct families that account for the seven species recognized globally. Six species belong to the family Cheloniidae, known as the hard-shelled turtles. They all possess carapaces constructed of bony plates covered by keratinous scutes.
- Green turtle
- Loggerhead turtle
- Hawksbill turtle
- Flatback turtle
- Kemp’s ridley turtle
- Olive ridley turtle
The seventh species, the leatherback turtle, is the sole surviving member of the family Dermochelyidae. Unlike their hard-shelled relatives, leatherbacks lack a bony carapace. Instead, their shell is composed of a mosaic of tiny bones embedded in thick, dark, leathery skin, representing a significant evolutionary divergence.
Profiles of the Seven Global Species
Leatherback Turtle (Dermochelys coriacea)
The leatherback is the largest sea turtle species, growing up to six feet in length and weighing over 1,400 pounds. It is recognizable by its dark, leathery carapace, which features seven distinct longitudinal ridges. Leatherbacks are deep-diving, pelagic animals that forage primarily on gelatinous zooplankton, such as jellyfish and salps, throughout the Atlantic, Pacific, and Indian Oceans.
Green Turtle (Chelonia mydas)
Named for the greenish color of their body fat, adult green turtles are the only herbivorous sea turtles, feeding exclusively on seagrass and algae. They possess a smooth, dome-shaped carapace and a serrated lower jaw adapted for grazing. Green turtles are widely distributed in tropical and subtropical waters worldwide, with highly dispersed nesting sites.
Loggerhead Turtle (Caretta caretta)
Loggerheads are distinguished by their large head and powerful jaws, adapted for crushing the hard shells of prey like mollusks, crabs, and conchs. Their carapace is reddish-brown and has a somewhat heart-shaped appearance with five pairs of lateral scutes. These omnivorous turtles inhabit temperate and tropical regions of the Atlantic, Pacific, and Indian Oceans, undertaking vast migrations.
Hawksbill Turtle (Eretmochelys imbricata)
The hawksbill turtle is named for its narrow, pointed beak, which resembles a raptor’s and allows it to reach into coral reef crevices. Its patterned shell, made of thick, overlapping scutes, was historically sought after for the tortoiseshell trade. Their specialized diet consists mainly of reef sponges, which contain indigestible glass-like spicules that the turtles are uniquely able to process.
Kemp’s Ridley Turtle (Lepidochelys kempii)
Kemp’s ridley is the smallest sea turtle species, typically weighing less than 100 pounds and having a nearly round, grayish-green carapace. They are primarily coastal turtles, found in the temperate to subtropical waters of the western Atlantic Ocean and the Gulf of Mexico. This species prefers sandy or muddy bottoms where they feed on benthic organisms, primarily crabs.
Olive Ridley Turtle (Lepidochelys olivacea)
Named for its olive-green carapace, the olive ridley is the second smallest species, reaching lengths of about two and a half feet. A key feature is the highly variable number of lateral scutes on its carapace, often having six or more pairs, a higher count than most other species. This omnivorous species is found in tropical regions of the South Atlantic, Pacific, and Indian Oceans, and is famous for its synchronized, mass nesting events called arribadas.
Flatback Turtle (Natator depressus)
The flatback turtle is unique because of its restricted geographical range, found almost exclusively in the waters around Australia and Papua New Guinea. Its name describes its relatively flat, smooth, olive-gray carapace, which is thin and has upturned edges. Flatbacks are carnivorous, foraging in coastal waters on a diet that includes sea cucumbers, soft corals, and various invertebrates.
Current Vulnerability and Conservation Status
The conservation status of the seven global sea turtle species is monitored by the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. The global status presents a spectrum of vulnerability reflecting varying population trends. For instance, the Kemp’s ridley and the hawksbill are classified at the highest risk level, Critically Endangered. Other species, including the leatherback and loggerhead turtles, are categorized as Vulnerable, though their subpopulations often face more severe threats. The flatback turtle is currently classified as Data Deficient, meaning there is insufficient information to assess its extinction risk. The green turtle has seen its global status re-assessed to the lower-risk category of Least Concern, a positive trend attributed to decades of protective measures.
The overall global status masks significant regional differences, as the IUCN assesses distinct nesting populations separately. While the green turtle’s global status is Least Concern, some Pacific subpopulations remain classified as Endangered. This variation underscores that while conservation measures have yielded positive results for some populations, others, particularly leatherbacks in the Pacific, continue to face decline.