Where do the turtles go? Green sea-turtle hatchling swim away, and they don't come back for years.
Every summer, thousands of endangered" green sea turtles climb onto beaches around the world. Each female digs a hole in the sand with her strong back flippers. After laying 100 or more eggs, she covers her nest with sand and swims away.
Two months later, the eggs hatch, and the two-inch-long baby turtles crawl out of the sand and disappear into the ocean. They don't reappear until they have grown as large as dinner plates. Until now, no one knew where the hatchlings went or what they did.
"If we don't know where these little turtles are, we can't protect them," says Kim Reich, who studies marine animals.
Reich helped solve part of the mystery. She used chemistry to test a 20-year-old idea that green sea turtles grow up in the open ocean.
Turtles in the Bahamas
Reich's story starts in the Bahama Islands. Her mentor, Karen Bjorndal, has studied green sea turtles hear Great Inagua Island for more than 30 years.
Large sea-grass meadows grow in the island's shallow bay. Many young sea turtles come here to live and eat at the end of their mysterious childhood.
These turtles are the only sea turtles that live as plant eaters. In fact, their name may be a result of their diet. The turtles don't look green. The coverings, or scutes, of their shells range in color from pale yellow to dark brown. But the reptiles do have green fat. Scientists learned that the turtles eat green sea grass and green algae, which may turn their fat green.
Every year, Bjorndal and Alan Bolten, another sea-turtle biologist, go to the Bahamas. For two weeks, they live in a one-room stone building close to the beach. There, they catch turtles, put identification tags on them, and count the turtles that have arrived since the year before.
Between 2002 and 2004, Bjorndal and Bolten captured 44 green sea turtles in the Bahamas. Before letting the turtles go, the biologists removed a small part of the scute from each turtle's shell.
Like a person's fingernails, a turtle's scute is made of keratin. And like a fingernail, once that scute material forms, it doesn't change. Scientists can "read" the chemicals captured in layers of scute to learn what kinds of food an animal ate when each layer was forming.
Bjorndal and Bolten took the samples to their laboratory in Florida, where Reich tested them. She found clues that support the 20-year-old idea: baby green sea turtles eat meat before they switch to a diet of plants. In fact, they eat animals that live in the open ocean.
"It was more exciting than surprising," Reich says. "It was very rewarding to see it come out the way that it did."
For years, scientists have looked for evidence of oceanic turtle nurseries. Of seven known species of sea turtles, only one has been found eating meat as a youngster. Very young loggerheads eat jellyfish and other small marine animals in the North Atlantic Ocean. A similar hot spot full of baby green sea turtles has not been found yet.
Clues from Loggerheads
"We knew' where the little loggerheads were, and we knew what they were eating," says Reich. "So, by comparing the chemical signatures of the little loggerheads with the green turtles, we could figure out what the green turtles were doing."
Reich compared the bits of green-turtle scute with pieces of loggerhead seute. The oldest bits of green-turtle scute had the same chemicals as the loggerhead scute. This means that the baby green turtles were doing the same sorts of things as baby loggerheads, in the same sorts of places.
These "plant-eating" sea turtles were eating jellyfish and other animals in the open ocean. Later, they would suddenly switch to a diet of plants.
Where Are the Nujseries?
Scientists still need to find the green sea-turtle nurseries. We now know that baby green sea turtles are out in the open ocean, but the open ocean is a big place.
"This has been a really intriguing and embarrassing problem for sea-turtle biologists, because so many green-turtle hatchlings enter the ocean, and we haven't known where they go," says Bjorndal The discovery may help scientists find the nurseries. Then we can do a better job of protecting this endangered marine animal.
Adult green sea turtles eat mainly plants.
Bady green sea turtles are oceangoing meat eaters.