San José, Costa Rica, since 1956

Marine Turtle Nests Affected by the Heat

PLAYA JUNQUILLAL, Guanacaste – Costa Rica’s sea turtles, already threatened, may face their worst foe yet if global warming and rising sea levels continue unchecked.

Climate change, according to the country’s top scientists, could attack ailing turtle populations, driving them to the brink of extinction after nearly 100 million years on earth.

On the Pacific coast, dark, volcanic beaches are quickly turning into steaming cauldrons that threaten to hard-boil turtle eggs and alter age-old processes of sex-determination.

On the Caribbean, rising sea levels and torrential rains are encroaching on shallow beaches, and shifting ocean currents worldwide threaten to disorient turtles and alter the sea’s intricate food web.

To understand the problem, says Gabriel Francia, an Argentinean biologist who has studied turtles at Playa Junquillal, in the sun-drenched northwestern province of Guanacaste, since 2001, just dig in the sand.

“Feel how hot the sand is, “ he says. “If we don’t transplant these nests to the shade, the eggs will all die.”

As the heat ratchets up, biologists wonder if the turtles, already faltering and faced with countless threats from poaching and pollution to high seas fishing and beachfront development, will be able to cope.

Major Changes

Sea turtles are no strangers to change – they co-existed with dinosaurs, and outlived the last Ice Age.

The one enemy they hadn’t accounted for was humans.

“The climate changes are coming too rapidly for the turtles to adapt,” explains Carlos Drews, a Cambridge-educated Colombian biologist who now manages the marine program for the World Wildlife Fund (WWF) in Latin America.

The international nonprofit organization, one of the world’s largest, plans to kick off a series of studies later this month that will better quantify the effects of global warming on sea turtles, and design measures to reduce their impact.

According to the International Panel on Climate Change (IPCC), temperatures will likely rise, between 1.8 to 4 degrees Celsius (3.1 and 7.2 degrees Fahrenheit) by 2090, and ocean levels will follow suit as arctic ice continues to melt (TT, June 15).

Because the temperature of the sand around a turtle egg determines the sex of the embryo, turtles, perhaps more than any other species, will become victims of circumstance, Drew explained.

A turtle hatched in sand above an average of roughly 29° C (84° F) will be female, below that temperature, male. The ideal ratio for the long-term survival of a species, he says, is 50% male, 50% female.

“The very few leatherback eggs that survive the extreme heat of the summer season hatch as mostly females,” Drews said, adding that this skewed ratio could quickly compromise already ailing populations.

Francia routinely observes lethal temperatures upwards of 40° C (104° F) inside nests on Playa Junquillal, and has measured exposed sand temperatures as high as 70° C (158° F).

“If we don’t move the eggs to the shade, they die,” Francia said.

All species of sea turtles are susceptible to this cruel fate, but perhaps none more than the lumbering leatherback, which can grow as large as a Volkswagon Beetle.

“They are the only turtle to nest exclusively in the dry season, beneath clear skies,” at the peak period of sun radiation,” Drews explained.

Other species – the olive ridley, the green and the hawksbill, are slightly more fortunate: they nest at least part of the year beneath the cooling clouds and rain of the wet season – and so are shielded from the inferno faced by baby leatherbacks.

But the problems, say global warming experts, don’t fizzle with the sun.

Two hundred miles away but a world apart from Guanacaste’s parched, sweltering landscape, the jungles of the verdant northeastern Caribbean coast drip with water –more than 5 meters (200 inches) of rain falls annually – and the beaches are often shrouded in mist and clouds.

“There are different issues for different coastlines, but the effects in terms of loss of habitat will ultimately be the same,” said Emma Harrison, scientific director for the Caribbean Conservation Corporation (CCC), which works to protect sea turtles on the country’s east coast.

Rainfall patterns are shifting, according to the National Meteorological Institute, and the Caribbean will bear the brunt of heavier, more frequent rainfall.

Harrison believes this could mean flooding from below. In essence, a rising water table could drown turtle eggs. It’s already happening, she said.

“Leatherbacks dig the deepest nests.

They’re already hitting the water table in some places,” she said.

She also worries about rising sea levels –and its effects on all turtles, not just leatherbacks.

“Our beach is dynamic. It’s not what you find on the Pacific – one extreme high tide and the waves wash across the beach,” she said.

Last week, she said researchers at Tortuguero found a nest whose eggs were black.

“They’d sat in water for too long,” she said.

The turtle embryos had died.

What Next?

Back at Junquillal, Francia is taking no chances: During the dry season he transplants every leatherback nest he locates to a shaded hatchery, and waters it periodically each day to keep it cool. The hatchery is fenced to protect it from stray dogs, and closely monitored, day and night.

He does the same for the nests of olive ridleys and the scattered Pacific green, in an effort to keep the male-female ratios of all species in balance.

He digs another shallow hole – this one beneath the dark mantle of the hatchery’s shade cloth, and reveals a sandy lair that’s cool to the touch, and moist.

“It helps. But even in the shade, we rarely get the temperature we want during the dry season.We do what we can,” he said.

In addition to the oft-mentioned solution – reducing emissions to stem global warming – turtle experts insist that protecting the beachfront from development, and keeping it forested, is critical to turtle survival.

Flexible park boundaries to accommodate changing coastlines and turtle needs are also critical.

Lacking those protections, biologists turn to “unnatural” last-ditch measures, such as the Junquillal hatchery.

“In the past, species like turtles have adapted to changes by natural selection. But the climate is changing too rapidly. This is no longer a natural problem. We cannot expect them to adapt,” Drews said.

To beat global warming and save the turtles, biologists must look to a counter-intuitive approach, he said.

“We must be most concerned with the threats not associated with global warming, so populations are stronger. We need to be sure every egg hatches, every baby leatherback lives, so they’re best equipped to survive the new challenges they face,” Drews concluded.


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