Chelonia mydas

Lore & Background

The green sea turtle is a long-lived, highly migratory marine reptile. Juveniles spend the first several years of life in pelagic surface currents, drifting across open-ocean gyres before transitioning to neritic (coastal) habitats as they mature. Adults establish relatively stable foraging grounds, often in shallow seagrass beds, mangrove-adjacent shallows, or coral-reef lagoons, where they graze continuously on vegetation. Males and females disperse widely between foraging sites and nesting beaches, with some individuals traversing hundreds or even thousands of kilometres over a single migratory cycle. Navigation is thought to rely on a combination of geomagnetic field sensing, ocean-current cues, and possibly olfactory landmarks, allowing adults to return to their natal beach to nest—a behaviour known as natal homing.

Reproduction is tied to temperature-dependent sex determination: incubation temperatures above roughly 29 °C produce predominantly female hatchlings, while cooler ranges favour males. Females nest on sandy beaches, typically at night, depositing clutches of 100–200 eggs. Hatchlings that successfully reach the sea enter the pelagic juvenile phase, completing a life cycle that can span five to eight decades. The species is the only surviving member of its genus; all other Chelonia species are known from the fossil record.

Ecologically, green sea turtles are functional keystone species in seagrass ecosystems. Their continuous grazing trims seagrass shoots, stimulates new growth, and maintains the structural complexity that shelters juvenile fish, crustaceans, and invertebrates. Removal of adult turtles from a seagrass bed leads to overgrown, senescent vegetation and a measurable decline in associated biodiversity, a relationship documented in multiple long-term field studies across the Caribbean, Australia, and the Indian Ocean.

Reader's Guide

IUCN Red List – Endangered (assessed 2019). The IUCN classifies Chelonia mydas as Endangered, reflecting a multi-decadal population decline driven by cumulative threats. The assessment notes that global nesting populations remain well below historical levels, with some regional populations (e.g., parts of the western Atlantic and the Indian Ocean) showing continued downward trajectories. Recovery is uneven: a few well-managed sites in the Caribbean and Australia show stabilising or modestly increasing nesting counts, but these gains are fragile and highly sensitive to local disturbance.

CITES Appendix I (since 1975). Listing under Appendix I prohibits all international commercial trade in live animals, eggs, and derived products. Enforcement, however, remains inconsistent; illegal egg and meat trade persists in parts of Southeast Asia, the Indian Ocean, and the Caribbean, often through local black markets that circumvent the international-trade framework. Non-governmental monitoring and national enforcement capacity are the primary countermeasures, but resource gaps are significant.

Bycatch in commercial and artisanal fisheries. Green sea turtles are incidentally captured in longlines, gillnets, trawls, and shrimp trawls across the Atlantic, Indian, and Pacific Oceans. Mortality occurs through drowning, injury, or post-release stress. Turtle excluder devices (TEDs) in shrimp trawls and circle hooks in longline fisheries have reduced bycatch rates in some regions, yet adoption is voluntary in many jurisdictions, and compliance is uneven. No single global mandate covers all gear types.

Coastal development and habitat degradation. Construction of coastal infrastructure, beach armoring, and light pollution disrupt nesting beaches and degrade foraging habitats (seagrass meadows, mangroves). In many tropical nations, zoning and environmental-impact-assessment regulations exist on paper but are under-enforced. Marine protected areas (MPAs) that include both nesting beaches and foraging grounds offer the strongest protection, yet they cover a small fraction of the species' range.

Climate change and temperature-dependent sex determination. Rising sand temperatures at nesting sites skew hatchling sex ratios toward female, threatening long-term population viability. No large-scale active intervention (e.g., shading, sand translocation) has been deployed at the scale needed. Research continues, but the trajectory of beach-temperature rise outpaces current adaptive capacity.

Did You Know?

• The green sea turtle is the only extant species in the genus Chelonia; all its congeners are known solely from the fossil record.
• Adults can remain submerged for several hours while resting or sleeping on the seafloor, but must surface regularly to breathe—juveniles in the open ocean can stay submerged for 4–7 hours.
• A single female may nest on the same beach for decades, timing her visits to the same lunar and tidal window each season, a fidelity documented in long-term mark-recapture studies.
• Green sea turtles are among the few vertebrates whose sex is determined entirely by incubation temperature rather than by chromosomes, making them acutely vulnerable to even small shifts in beach sand temperature.