Sea Turtle Facts

The green sea turtle is classified within the kingdom Animalia, phylum Chordata, and class Reptilia. It belongs to the order Testudines, which encompasses all turtles and tortoises. Within the superfamily Chelonioidea (the marine turtles), it is a member of the family Cheloniidae, which includes all hard-shelled sea turtles. Its scientific name, Chelonia mydas, firmly establishes its genus, while the common name "green sea turtle" is actually a misnomer regarding its external appearance; the name derives from the greenish color of its subdermal fat, a direct result of its heavily chlorophyll-based diet.

Marine turtles evolved from terrestrial ancestors during the early Cretaceous period, approximately 110 million years ago. Over millennia, they developed highly specialized morphological adaptations for an entirely pelagic lifestyle, returning to land solely to reproduce. Chelonia mydas specifically diverged by adapting to exploit the vast, nutrient-rich coastal meadows of marine angiosperms (seagrasses) that few other large vertebrates can utilize.

A mature green sea turtle is a massive reptile, typically measuring between 2.5 and 4 feet in carapace length and weighing anywhere from 150 to a staggering 350 pounds. Their defining feature is their shell, which is anatomically fused to their rib cage and spine. The dorsal shell, known as the carapace, is smooth, broad, and heart-shaped, typically featuring a mottled blend of brown, olive, gray, and black. The ventral shell, or plastron, is a pale, yellowish-white.

Unlike terrestrial tortoises, marine turtles cannot retract their heads or flippers into their shells for protection. Their limbs are highly modified into elongated, paddle-like flippers. The powerful foreflippers generate primary thrust for swimming, allowing them to reach burst speeds of up to 20 mph, while the hind flippers act as rudders for precise steering.

To survive in a hyperosmotic (high-salt) marine environment, green sea turtles possess large, specialized lachrymal glands located behind each eye. These "salt glands" actively pump excess sodium and chloride from their bloodstream, secreting it as viscous, salty tears, a physiological necessity since they ingest significant amounts of seawater while feeding. Their respiratory physiology allows for prolonged breath-holding; while resting or sleeping on the reef, a green sea turtle can remain submerged for several hours by drastically slowing its heart rate to conserve oxygen.

Green sea turtles boast a circumglobal distribution, inhabiting the tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans. They range widely along the coasts of over 140 countries, including the United States, Mexico, Costa Rica, Australia, and Indonesia.

Their habitat usage is highly ontogenetic (changing as they develop). After hatching, neonates enter the open ocean, spending several years in a pelagic phase where they drift in massive oceanic convergence zones and associate with floating sargassum mats. Once they reach a juvenile carapace length of approximately 20 to 25 centimeters, they undergo a drastic habitat shift, migrating to shallow coastal benthic foraging grounds. These nearshore habitats—predominantly lush seagrass meadows, coral reefs, and coastal bays—serve as their primary developmental and adult habitats.

The green sea turtle is unique among the seven species of sea turtles due to its ontogenetic dietary shift. As pelagic hatchlings and small juveniles, they are omnivorous, feeding opportunistically on macroplankton, jellyfish, ctenophores, and small pelagic crustaceans.

However, upon recruiting to coastal foraging grounds, they transition to strict herbivory. Adult Chelonia mydas feed almost exclusively on various species of seagrass and marine macroalgae. Their jaws are specifically adapted for this diet; the edges of the lower jaw are highly serrated, like a saw, allowing them to cleanly crop fibrous seagrass blades without uprooting the entire plant. This grazing behavior acts similarly to a lawnmower, preventing the seagrass from growing too tall and shading itself out, thereby increasing the overall health, growth rate, and nutrient content of the meadow—a classic example of a keystone species role.

Green sea turtles are generally solitary, independent creatures, though they frequently aggregate in high numbers at prime foraging grounds or basking sites. Unlike most marine turtles, green sea turtles in certain regions, such as Hawaii and the Galapagos Islands, exhibit terrestrial basking behavior, crawling onto undisturbed sandy beaches during the day to elevate their body temperature and rest.

Their most spectacular behavior is their epic reproductive migration. Adult green sea turtles exhibit highly precise natal homing, meaning females will migrate thousands of miles across open ocean basins to return to the exact geographic region—and often the exact stretch of beach—where they were hatched decades earlier. Navigation is achieved via an innate magnetic compass; the turtles detect both the intensity and the inclination angle of the Earth's geomagnetic field to pinpoint their natal shores.

The life cycle of the green sea turtle is incredibly slow and fraught with high mortality in the early stages. They are extremely late-maturing, with wild individuals typically requiring 25 to 35 years to reach sexual maturity.

Mating occurs in offshore waters near the nesting beaches. After copulation, the female hauls herself onto the beach at night to avoid thermal stress and terrestrial predators. Using her hind flippers, she meticulously excavates a deep, flask-shaped egg chamber in the sand. She deposits a clutch of approximately 100 to 200 soft, leathery eggs, covers them with sand to regulate temperature and humidity, and returns to the sea. A female may nest 3 to 5 times in a single season before returning to her foraging grounds.

Incubation lasts 45 to 70 days. Sea turtles exhibit temperature-dependent sex determination; warmer sand temperatures produce predominantly female hatchlings, while cooler temperatures yield males. Upon hatching, the tiny neonates wait for nightfall before digging in unison to the surface. They rely on visual cues—specifically, the natural moonlight reflecting off the ocean—to guide their frantic scramble to the water, running a gauntlet of crabs, birds, and raccoons. Green sea turtles have a remarkable longevity, often living 60 to 70 years or more in the wild.

(Population and conservation trend data sourced from the IUCN Red List of Threatened Species)

The green sea turtle is currently classified as Endangered on the IUCN Red List, with a globally decreasing population trend. Historically, they were decimated by commercial harvesting for their meat, fat (used for turtle soup), and eggs.

Today, anthropogenic threats remain severe. Incidental bycatch in commercial fisheries (particularly longlines, gillnets, and trawls) causes massive drowning mortalities. Marine plastic pollution is highly lethal; turtles often mistake floating plastic bags for jellyfish, leading to fatal gastrointestinal blockages. Furthermore, they are highly susceptible to fibropapillomatosis (FP), a debilitating tumor disease closely linked to agricultural runoff and coastal water pollution.

Coastal development drastically impacts reproductive success. Artificial beachfront lighting disorients emerging hatchlings, drawing them away from the ocean and toward roadways where they die of dehydration or predation. The destruction of nesting beaches via seawall construction and the loss of seagrass foraging grounds continue to threaten their long-term survival.

• IUCN Red List: Green Turtle
• WWF: Marine Turtles
• NOAA Fisheries: Green Turtle
• Sea Turtle Conservancy: Green Sea Turtle Information