Rising Sea Levels Wreaking Havoc on Sea Turtle Habitat in Africa

Sea levels on the coast of Bioko Island, Equatorial Guinea, may rise 2 1/2 feet by 2100, which could wipe out nearly 90% of the nesting habitat for sea turtles in the area.

Sea turtle seen while scuba diving. (Courthouse News photo / Bill Girdner)

(CN) — For millions of years, sea turtles have combed the oceans, hunting jellyfish and eating seagrass. These gentle giants spend much of their time at sea, migrating toward land mostly to nest and lay their eggs on sandy beaches.

But rising sea levels connected to climate change threaten the survival of these marine reptiles, according to a new study. Sea turtles face an 87% decline in critical nesting habitat on the beaches of Bioko Island, Equatorial Guinea, in the coming decades as oceans intrude on their natural nurseries, researchers from Purdue University and the University of Hawaii found.

The sea level near Bioko Island is predicted to rise as much as 2 ½ feet by 2100, according to “Predicting the impacts of sea level rise in sea turtle nesting habitat on Bioko Island, Equatorial Guinea” published by the journal PLOS One.

“Due to low elevations and limited capability for shoreline retreat, small islands are at the greatest risk from climate change,” the authors explained. Expected effects include increased salinity, beach erosion, and greater volumes of sand carried by rising tides.

There are seven species of sea turtles. The study focused on leatherbacks and green turtles.

In recent years, the Great Barrier Reef green sea turtle nesting population, the largest in the world, has struggled to protect their eggs as warmer temperatures and human development have altered the beaches they rely on to incubate their offspring. Green turtles prefer to nest on narrower beaches and behind the vegetation line, but rising oceans are already forcing them to nest “uncharacteristically” in front of vegetation where their nests are more likely to be flooded by the tide.

“Green turtles often struggle to reach the vegetation line, as they are unable to surmount steep vegetation berms or become entangled in overhanging root systems where the sand has eroded away,” the study authors found.

Leatherback returning to the ocean after a nesting attempt on Beach E, Bioko Island, Equatorial Guinea. (Callie Veelenturf)

Using GPS and 3D modeling, the study was conducted from October 2016 through February 2017, coinciding with the leatherback and green sea turtle nesting season on Bioko Island. Data from nest locations of both species were used in the study.

Researchers found that sea level rise is causing beach erosion to occur faster than the rate of shoreline retreat, destroying the habitat the turtles depend on for nesting.

“As sea level rises and beach erosion progresses, however, potentially eroding steeper and narrower beaches first and causing unsurmountable berms along the vegetation line, green turtles may be first to lose their nesting beaches altogether,” the study concluded.

Sea turtles are not mere throwbacks to the age of the dinosaurs. Like other marine reptiles, they are hearty survivors who have evolved with natural coastal erosive processes such as high-tide flooding, accretion and seasonal erosion. But extreme changes in beach conditions over the past 50 years have outpaced their ability to adapt.

“With an overall reduction in nesting habitat, if the rate of shoreline retreat continues to lag behind that of beach erosion, the density of nests will likely increase within the area of available nesting habitat,” according to the study. “This has potential to cause decreased hatching success through increased contamination and physical disturbance of nests.”

One possible solution is for scientists to create hatcheries to protect nests threatened by higher tides and warmer temperatures. But that approach carries risks.

“Although translocating nests can negatively affect embryo development, the relocation of otherwise doomed eggs to a hatchery can result in a net gain in hatchlings produced over time,” researchers noted.

The study, the first to examine sea turtle habitats in Africa, was funded by HESS Equatorial Guinea, Inc. as a grant to Purdue University Fort Wayne under Dr. Frank Paladino.

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