Though their ancestors once swam the seas alongside dinosaurs, the turtles of today are in danger. An estimated 61 percent of the world’s 356 species are threatened or already extinct in a loss that could have ecosystem-wide implications.
In the first major review of turtles, a paper published in BioScience synthesized existing published studies to offer a look at the species’ global status and the ecological role they play. Despite being some of the most recognizable animals on the planet, these creatures are being pushed to their breaking point.
As noted in the study, the word turtle actually encompasses tortoises and terrapins too, as it technically refers to "all animals with a bony shell and a backbone". Turtles are aquatic, tortoises live on land, and terrapins live only in fresh water.
“Turtles are struggling to persist in the modern world, and that fact is generally unrecognized or even ignored,” wrote the authors, who argue that turtles are the “most threatened of the major groups of vertebrates in general and are proportionately more so than birds, mammals, fishes or even the much-besieged and heavily publicized amphibians.”
Habitat destruction, over-exploitation for pets and food, disease, and climate change (many turtles’ gender is determined by their environment) are all threatening the species. In fact, some are no longer found in their native habitats and exist only in captivity. For example, there is only one known female Yangtze giant softshell turtle (Rafetus swinhoei), and for the last eight years, she has not produced fertile eggs despite international efforts to help her, including artificial insemination. Other species, like the Burmese star tortoise (Geochelone platynota), require captive breeding and intensive management to keep them from going extinct.
Aside from humans, turtles play one of the most significant roles in their individual ecosystems and inhabit a variety of environments around the world, ranging from arid to aquatic. As the authors note, their declines lead to negative impacts on other species – including humans – that aren’t immediately known.
As herbivores, omnivores, and carnivores, the diverse feeding habits of turtles influence and help maintain food webs as they take the roles of both predator and prey. They eat a range of plants and animals, and in return turtles and their eggs are prey to a variety of predators. Tortoises are important in dispersing seeds of plants, often acting as primary dispersal agents. The germination rates of some seeds actually improve when they've been passed through a tortoise's digestive system.
The reptiles are also essential in creating habitats. Take the gopher tortoise (Gopherus polyphemus), whose 9-meter-long (30-foot) burrows provide both soil habitat for plants and shelter for a variety of animals, including insects, reptiles, amphibians, and mammals.
“The fate of turtles is especially tragic in light of their distinction as paragons of evolutionary success,” wrote the authors. “They survived everything nature could throw at them from both Earth and outer space (e.g., the asteroid that wiped out the dinosaurs), but will they survive modern humans?”