Green sea turtle: The undersea lawnmower named for green fat

The green sea turtle's name sounds as if it means "green shell" — but it does not. Its name comes from the layer of green fat inside its body. It is a large member of the sea turtle family and one of the few turtles that switches to a plant diet as it grows. Let's meet it.

Its body and its name

The green sea turtle measures about 0.8 to 1.2 metres, with a broad, flat shell and paddle-like flippers. The "green" in its name comes from the green fat beneath its shell — a colour closely tied to its diet. Young green turtles are omnivores, eating small creatures and shrimps; as adults, though, they become nearly vegetarian, grazing almost entirely on seagrass and seaweed.

Its important work

Because adult green turtles eat seagrass, they are vividly nicknamed "undersea lawnmowers". By constantly cropping the grass they keep seagrass meadows neat and healthy and help nutrients circulate through the water. Seagrass meadows are home to many small fish and seahorses, so the green turtle is really guarding a whole marine ecosystem.

How it returns to its birthplace

The green turtle's navigation is astonishing: after decades roaming the open ocean it still finds the beach where it hatched. It uses the Earth's magnetic field, plus remembered clues. Females come ashore and lay dozens of eggs in a pit in the sand.

Sex and climate

Like many sea turtles, a green turtle hatchling's sex is decided by the sand's temperature: warmer sand produces more females. So a warming climate does not only change sea temperatures — it quietly affects the sex balance of the turtle family, making the protection of green turtles and of the climate inseparable.

A note for grown-ups

You could talk with a child about how sea turtles eat their greens: adult green turtles graze almost only on seagrass. Then wonder together: if there were no turtle to "mow" it, what would happen to the seagrass meadow? Helping a child feel how one animal affects a whole environment is a fine lesson in ecology.