Researchers discover what higher tides mean for turtles at one of the world’s most important nesting sites.
Due to climate change, the world’s ocean levels are rising and we’re only beginning to understand the different impacts those changes will have. Even for species that live most of their lives at sea, the rising tides could be a problem.
Researchers at Raine Island, an Australian island that’s part of the Great Barrier Reef, have found how sea level changes are bad for green sea turtles (Chelonia mydas). Raine Island is an important nesting ground for the endangered turtles, with up to 100,000 females nesting on its beaches each year.
But sadly, the number of young turtles that hatch from nests on Raine Island has been declining for the past two decades. Today, the number of eggs that hatch may be as low as 12 percent, compared to an average of over 80 percent at other nesting sites around the world. One possible explanation for the decline is frequent storms and bigger tidal waves, which inundate the nests with salt water.
Turtle embryos still need oxygen, and submerging the egg for too long can prevent the normal exchange of gasses through the egg’s membrane. Dr. David Pike at James Cook University and colleagues found that after six hours of salt water submersion, an egg’s chances of hatching decrease by 30 percent. Although salt water submersion is not always deadly, the researchers say they don't know how it might also be affecting the unhatched turtle's development.
Their study is published in the journal Royal Society Open Science. The finding may help explain what's happening not only on Raine Island, but also what might lay ahead for other nesting grounds should sea levels continue to rise unchecked.
More frequent storms and sea level rise aren’t the only threat to green sea turtles. Habitat degradation from pollution is also a problem, and hunting these turtles remains legal in many parts of the world. According to the International Union for Conservation of Nature, the presence of artificial lights on or near beaches can also affect the nesting turtles' behavior, as well as confuse hatchlings and interfere with their ability to reach the sea.
Higher sea levels may also decrease the area of beach available to turtles to build nests. “Rising sea levels and storms will have profound effects on coastal habitats by inundating eggs, reducing nesting areas by altering beach geomorphology, depositing new sand, or depositing debris that can act as barriers for nesting females or emerging hatchlings,” write the authors.