Natalie Parletta
Natalie Parletta is a freelance science writer based in Adelaide and an adjunct senior research fellow with the University of South Australia.
These slow, gentle creatures have inhabited the Earth and its oceans for more than two million years. They’ve outlived the dinosaurs. But turtles have met their match in modern humans – and a comprehensive review of the global situation reveals this could have far-reaching ecological consequences.
“Turtles contribute to the health of many environments, including desert, wetland, freshwater and marine ecosystems, and declines may lead to negative effects on other species, including humans, that may not be immediately apparent,” warns lead author Jeffrey Lovich of the US Geological Survey in Flagstaff, Arizona.
The paper shows that turtles are among the most threatened of the major groups of vertebrates on the planet – of the 356 species of turtles worldwide, approximately 61% are threatened or already extinct, victims of habitat destruction, over-exploitation for pets and food, disease and climate change.
Tens of millions of turtles were estimated in the Caribbean Sea just two centuries ago. They are now thought to number in the tens of thousands.
But, as the study points out, the disappearance of turtles will have disastrous effects on a range of systems.
Turtles’ diverse feeding habits contribute to their extensive role in ecosystem food webs. The animals can be herbivores, omnivores and carnivores, and either specialise in one or a few food sources, or feed on a wide variety of foods.
And without them, things can quickly go horribly wrong.
The small diamond-back terrapin (Malaclemys terrapin), for example, feeds on periwinkle snails (Littorina irrorata). Experimental evidence shows that without these predators, perwinkle snails could reduce productive grasslands to “barren mudflats” in just eight months.
Together with their eggs, turtles in turn provide a major food source for an assorted array of predators including vertebrates and invertebrates.
Their scavenging, meanwhile, cleans up waste, a major contributor to the flow of energy through an ecosystem.
The review highlights three Australian turtle species, for example, which consume an estimated 430 tonnes of carrion per day over 358,000 hectares during summer.
Turtles also spread seeds for dozens of plant species. For some plants, turtles may be the only means of seed dispersal. In other species, seeds germinate faster after passing through turtles’ digestive tracts.
Many turtles are diggers and burrowers, vital for soil dynamics, and increasing plant diversity that provides habitats for hundreds of other species.
Any animal with a bony shell and backbone identifies as a turtle, and no vertebrate animal has ever had such a unique structure. “If they were known only from fossils, they would be cause for wonder,” write the authors.
The report catalogues the lost species and those about to vanish.
The Pinta giant tortoise (Chelonoidis abingdonii), for example, became extinct in 2012 when its last surviving member, “Lonesome George”, died in the Galápagos Islands.
Only four surviving Yangtze giant softshell turtles (Rafetus swinhoei) are known to exist – and that’s in captivity.
The “beautiful Burmese star tortoise (Geochelone platynotan) and the less charismatic western swamp turtle (Pseudemydura umbrina), Australia’s rarest reptile,” are two more of the world’s 25 most endangered turtle species, the authors report.
The authors say urgent action is needed. Global conservation programs focus on protecting birds and mammals, but there has been less focus on turtles.
“The alarming rate of turtle disappearance could profoundly affect how ecosystems function and the structure of biological communities around the globe,” says coauthor Josh Ennen.
“We must take the time to understand turtles, their natural history, and their importance to the environment,” urges UC Davis scientist Mickey Agha, “or risk losing them to a new reality where they don’t exist.”
