Green Sea Turtle

Overview

The green sea turtle is one of the largest hard-shelled sea turtles, with adults typically weighing 150-200 kg and reaching carapace lengths of 1-1.2 meters. This species is distinguished by its relatively small head, single pair of prefrontal scales, and smooth carapace that varies from olive to dark brown, often with radiating patterns. The common name derives from the greenish color of its body fat, which results from its herbivorous diet. Green sea turtles inhabit tropical and subtropical waters worldwide, favoring coastal areas with seagrass beds and algae-rich reefs where adults feed. Juveniles are more pelagic and carnivorous, while adults undergo a dietary shift to become primarily herbivorous, grazing on seagrasses and algae. This feeding behavior plays a crucial ecological role in maintaining healthy seagrass beds and coral reef ecosystems. The species undertakes remarkable migrations, with individuals traveling hundreds to thousands of kilometers between feeding grounds and nesting beaches. Females return to the same beaches where they hatched to lay their eggs, displaying remarkable natal homing abilities. Despite their wide distribution, green sea turtles face numerous threats including habitat loss, fisheries bycatch, marine pollution, and climate change impacts on nesting beaches and sex ratios. Historically hunted extensively for their meat, eggs, and shells, green sea turtle populations have declined significantly worldwide. Conservation efforts including nesting beach protection, fishing gear modifications, and international trade restrictions have helped some populations stabilize or recover, though the species remains endangered globally.

How to identify

Adults have a smooth, oval carapace 80-150 cm long, colored olive-brown to black with variable patterns. Distinguished by a single pair of prefrontal scales between the eyes (versus two pairs in hawksbill turtles), a rounded blunt head, and serrated lower jaw. Four pairs of coastal scutes on carapace, non-overlapping. Limbs modified into large flippers with one visible claw. Hatchlings are dark gray to black dorsally with white undersides. No vocalizations in adults; hatchlings may produce soft sounds during emergence.

Habitat

Tropical and subtropical coastal waters including seagrass meadows, algal reefs, shallow lagoons, and sheltered bays. Adults prefer areas with abundant seagrass and macroalgae at depths typically less than 20 meters. Juveniles are initially pelagic in open ocean before recruiting to coastal habitats. Nesting occurs on sandy tropical and subtropical beaches worldwide.

Distribution

Circumglobal distribution in tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans. Major nesting populations in Costa Rica, Australia, Indonesia, Malaysia, and scattered sites in the Caribbean, Mediterranean (Cyprus, Turkey), East Africa, and Pacific islands. Feeding aggregations found along continental shelves and around oceanic islands between approximately 40°N and 40°S latitude.

Diet

Juveniles are omnivorous to carnivorous, feeding on jellyfish, mollusks, crustaceans, fish eggs, and sponges. Adults undergo dietary shift to primarily herbivorous diet, grazing on seagrasses (especially Thalassia, Zostera species) and macroalgae. This herbivory maintains seagrass health through grazing and nutrient cycling. Some geographic populations may supplement diet with invertebrates and carrion.

Behavior

Highly migratory, traveling thousands of kilometers between feeding and nesting areas. Adults exhibit strong site fidelity to specific feeding grounds. Capable of long, deep dives (up to 40 minutes, though typically 4-5 minutes) when foraging or resting. Often observed basking at the surface or resting on beaches in Hawaii and Galapagos. Generally solitary except during mating season. Can achieve swimming speeds of 35 km/h in short bursts.

Reproduction & life cycle

Sexual maturity reached at 20-50 years of age. Females nest every 2-5 years, returning to natal beaches. Nesting season varies by location but generally occurs in warmer months. Each female lays 3-7 clutches per season at 12-14 day intervals, with approximately 110-115 eggs per clutch. Incubation period 45-75 days depending on sand temperature. Temperature-dependent sex determination: warmer temperatures produce more females. Hatchlings emerge at night and crawl to sea, beginning pelagic juvenile phase lasting 3-5 years.

When to look

Nesting season varies regionally: March-October in Caribbean; November-February in South Atlantic; year-round in equatorial regions with peaks. Feeding activity year-round. Migration periods vary by population but often linked to seasonal breeding cycles.

Cultural significance

Historically important food source for many coastal cultures throughout its range, with meat, eggs, and calipee (cartilage) consumed. Shell used for decorative items and in traditional medicines in some Asian cultures. Sacred to many Pacific Island cultures and features in creation stories and folklore. Today serves as flagship species for marine conservation and ecotourism, particularly in Hawaii, Costa Rica, and Australia where turtle watching generates significant economic value.

Similar species

• Hawksbill turtle (Eretmochelys imbricata)
• Loggerhead turtle (Caretta caretta)
• Olive ridley turtle (Lepidochelys olivacea)

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