Turtle nesting grounds under threat from climate change, reports show

Mary River turtle. Photo credit: Daniela Parra on Flickr
Augusta Dwyer
24 May 2018

BONN, Germany (Landscape News) — When Australia’s Mary River turtle (Elusor macrurus) was featured in the news recently, its unusual appearance and characteristics may have overshadowed the fact that the Zoological Society of London had just added it to a new list of vulnerable reptile species.

Capable of breathing with its genitals, the turtle can spend up to three days underwater, allowing algae to grow on its body and often giving it what looks like a bright green, punk rock hairdo. That, together with its placid nature, has made it a popular pet, which has pushed it to the verge of extinction.

Around the world, turtles are under siege, but climate change remains the species’ biggest threat. According to a 2011 report from the U.S. Department of Agriculture Forest Service, half of freshwater species are vulnerable, more than any other animal group.

A study earlier this year, published in Current Biology, has found that rising temperatures are having an impact on another Australian turtle, the green sea turtle (Chelonia mydas).

Because sand temperature determines the gender of hatchlings, with warm sand producing females and cooler sand males, the latter are slowly disappearing.

In their paper, researchers from the U.S. National Ocean and Atmospheric Administration and the Queensland Department of Environment and Heritage Protection wrote that temperatures on islands in Australia’s northern Great Barrier Reef have increased to the point “that virtually no male turtles are now being produced from these nesting beaches.”

The scientists used an innovative combination of endocrinology and genetics to assess the gender of hundreds of turtles across a large foraging ground, revealing the sex ratio of immature and mature turtles from different nesting beaches over many years. They analyzed sex ratios and trends in two nesting populations. While the southern population they studied was about 65 to 69 percent female, more than 99 per cent of juveniles and subadults in the northern group were female.

“Our study,” the scientists wrote, “highlights the need for immediate management strategies aimed at lowering incubation temperatures at key rookeries to boost the ability of local turtle populations to adapt to the changing environment and avoid a population collapse—or even extinction.”

The projected rise in sea levels associated with climate change also threatens coastal freshwater turtles, as salty water intrudes into freshwater habitats, say scientists from the Department of Wildlife, Fish and Conservation Biology at the University of California, Davis (UC Davis) in an article recently published in Biological Reviews.

“We link together current knowledge of geographic occurrence, salinity tolerance, phylogenetic relationships, and physiological and behavioural mechanisms to generate a baseline understanding of the response of freshwater turtles to changing saline environments,” the paper stated.

According to Mickey Agha, a Ph.D. candidate at UC Davis and lead author of the study, the biologists overlapped median sea level rise projections of one metre by the year 2100 with the known distribution patterns of coastal freshwater turtles.

Some freshwater turtles lose body mass and can die when exposed to high levels of salty water, while others can tolerate a narrow range of salinities.

“For the behavioral and life history traits, we conducted a review of the literature,” said Agha. “Some 20 to 30 studies assessing how freshwater turtles cope with water salinity, and summarized them to get a grasp of which turtles are most sensitive, and also, which turtles have been caught in these brackish waters habitats and could be most at risk.”

Results indicated that freshwater turtles in North and South America, Southeast Asia, Australia and New Guinea – 15 species in all – are most at risk. Some of those species are already critically endangered, said Agha, while others form large communities.

It can take a long time for freshwater turtles to reach sexual maturity, sometimes up to 20 years, he said. “Can these turtles adapt fast enough to meet the pace of these climate change factors? The answer is no, unfortunately.”

Because turtles are central to the food web, their decline will have an effect on all kinds of other organisms. By cropping sea grasses on the ocean floor, for example, sea turtles keep the underwater environment healthy for many species of fish, shellfish and crustaceans.

“Freshwater turtles also eat the sea grass,” said Agha, “and transfer that biomass around the system, from the aquatic environment to the land, as they go back and forth. They also shape freshwater communities as predators, so by losing them and other turtles in general, we are potentially losing these critical species that support important ecosystem dynamics.”

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