A green turtle hatchling peeks from inside its shell. A hatchling is born with an attached yolk (red) which it will absorb over a week.

How Do Turtles Like Their Sand?

[ICCB 2019] For newly hatched green turtles, life starts in the dark. Nine weeks ago, a turtle’s mother would have climbed onshore, dug a hole 50 cm deep, laid more than a hundred eggs inside, then sealed it with sand. Now, the hatchlings must escape from their buried nest and dash to sea.

But does it matter what type of sand hatchlings have to power through to make it to the surface?

(Photo: A green turtle hatchling peeks from inside its shell. Hatchlings have an attached yolk (red) which they absorb over the course of a week. Credit: Lyvia Chong/SEATRU)

How the hatchlings make their way to the surface is a mystery, says Lyvia Chong Kai Syin, a turtle conservationist and graduate student researcher at Sea Turtle Research Unit (SEATRU), Universiti Malaysia Terengganu.

Chong has been working to understand the hatchlings’ “escape plan”—as she calls their attempt to emerge from underground. Her research examines how sand size might affect the hatchlings’ efforts.

She finds that fine sand actually prolongs hatchlings’ journey to the top. Hatchlings take 5 – 14 days to dig out of fine sand, but only 5 – 8 days in coarse sand. On average, hatchlings emerged from fine sand in 9.6 days and from coarse sand in 8 days. She presented her results on 25 July at the ICCB.

Energy saving

A longer emergence time might mean that hatchlings expend more effort, and hence energy, to dig through the sand. And energy is precious.

Hatchlings charge their ascent primarily by absorbing an attached yolk which they are born with. An easier climb to the surface should leave hatchlings with more energy and higher odds of survival.

In nature, female green turtles lay eggs in both sand types, says Chong. But her findings matter for ex-situ (off-site) turtle egg hatcheries. These hatcheries transfer eggs from natural nests to protected facilities and incubate them in sand.

What kind of sand though? “When we artificially manage the eggs,” Chong tells Macaranga, “where should we put them?”

Fine or coarse?

To find out, Chong is studying the hatchlings at SEATRU facilities on Redang Island, off the east coast of Peninsular Malaysia.

At the Turtle Lab (hosted in a resort), Chong sets up two cylinders—one filled with fine sand and the other, coarse sand. In each cylinder, she buries green turtle eggs one meter deep in the sand.

Green turtles are considered “Endangered” on the IUCN Red List. They are however, the most common sea turtle in Malaysian waters.

She gets the eggs from an on-site hatchery at the nearby Chagar Hutang Turtle Sanctuary. Eggs from the same nest are divided equally between the cylinders.

Time and oxygen

She records how long hatchlings take to emerge in numbers. Her setup also measures the amount of oxygen consumed in the cylinders. Higher oxygen usage indicates that the hatchlings are expending more energy.

Between May and August 2018, Chong used more than 2,000 eggs of 12 nests in her experiment. More than 85% of eggs in the experiment hatched, she says. All hatchlings were later released into the sea.

Shortly after Chong’s 2018 field work, a new study on loggerhead turtles in Japan published results similar to hers.

The November 2018 study found that hatchlings emerged faster when incubated in coarse rather than fine sand. But it also reported that hatchlings from fine sand could crawl and swim better.

The authors suggested that maybe it was less strenuous to dig through fine sand.

More experiments

RIght now, Chong cannot yet say if hatchlings expend more energy digging through fine or coarse sand. Unfortunately, half of her oxygen data was rendered useless by faulty equipment and power outages.

“But that’s okay because I’m running more samples now”, she says.

Her results will certainly help unveil more of the hatchlings’ escape plan, and hopefully improve hatchery success.

This is a part of our reporting on the International Congress for Conservation Biology, July 21-25, 2019, Kuala Lumpur.