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As turtles go, so go their ecosystems

As turtles go, so go their ecosystems

by Mongabay.com on 19 September 2018

  • Turtles are among the most threatened of the major groups of vertebrates in the world, a new review paper says, perhaps even more so than birds, mammals, fish or amphibians.
  • Of the 356 species of turtles recognized today, about 61 percent are either threatened or have become extinct in modern times.
  • Turtles contribute to the health of a variety of environments, including desert, wetland, freshwater and marine ecosystems, and losing these animals could have serious ecological consequences, researchers say.

Turtles were once a tough group of animals. Sea turtles survived the extinction event that wiped out the dinosaurs some 65 million years ago. But the modern descendants of this ancient group are struggling to survive.

Turtles are in fact among the most threatened of the major groups of vertebrates in the world, a new study says, perhaps even more so than birds, mammals, fish or amphibians. Of the 356 species of turtles recognized today, about 61 percent are either threatened or have become extinct in modern times.

For example, when Lonesome George, the last surviving Pinta giant tortoise (Chelonoidis abingdonii), died in June 2012, it was the end of an entire species. The Yangtze giant softshell turtle (Rafetus swinhoei) is also teetering on the brink of extinction. With only four surviving individuals — two in captivity in China and two in the wild in Vietnam — of which only one individual is known to be a female, researchers are struggling to revive the species.

Turtle populations around the world have been decimated by habitat destruction, overexploitation for food, the commercial pet trade, disease, and climate change. And the collapse of turtle populations could have serious ecological consequences, researchers say in a new paper in Bioscience that reviews the global status of turtles and the roles they play in our ecosystems.

“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,” lead author Jeffrey Lovich, an ecologist at the United States Geological Survey, said in a statement.

A hatchling Sonora mud turtle, which is found in Mexico and the United States. Image by Jeffrey Lovich, USGS.

Turtles can be predators or prey. They can be herbivores, omnivores and carnivores. They can be specialists, feeding on a few food sources, like the leatherback sea turtle (Dermochelys coriacea) that eats almost exclusively jellyfish. Or they can be generalists, feasting on a wide variety of food, like slider turtles that eat just about anything. Turtles and their eggs are important prey to a wide variety of predators. These reptiles graze, they dig burrows, they disperse seeds, they create and modify habitats, and they affect food webs and mineral cycling. Losing these animals can be disastrous, the review says.

For instance, the small diamondback terrapin (Malaclemys terrapin), found in the coastal tidal marshes of the eastern and southern United States and in Bermuda, are predators that feed on, and regulate, periwinkle snails (Littorina irrorata). Experiments show that without predators like the terrapin, periwinkle snails can convert productive grasslands in salt marshes to “barren mudflats” in just eight months.

Similarly, hawksbill turtles (Eretmochelys imbricata) help corals flourish. They consume sponges, which are competitively superior to coral, the study notes, and by doing so, the turtles help reduce competition for space within the coral reef and increase coral species’ richness and health.

Turtles can also restore ecosystems. After being decimated from the Galápagos Islands, giant tortoises are being reintroduced to some of the islands to help restore the native savanna-like ecosystems.

“Our purpose is to inform the public of the many critical ecological roles turtles perform on a global scale and bring awareness to the plight of these emblematic animals whose ancestors walked with the dinosaurs,” said Whit Gibbons, professor emeritus at the University of Georgia’s Savannah River Ecology Laboratory and Odum School of Ecology.

Wildlife ecologist Mickey Agha of the University of California, Davis, added: “We must take the time to understand turtles, their natural history, and their importance to the environment, or risk losing them to a new reality where they don’t exist. Referred to as a shifting baseline, people born into a world without large numbers of long-lived reptiles, such as turtles, may accept that as the new norm.”

Galápagos giant tortoise. Image by Matthew Field via Wikimedia Commons (CC by-SA 3.0).
A diamondback terrapin, a species native to the brackish coastal tidal marshes of the eastern and southern United States and Bermuda. Image by Jeffrey Lovich, USGS.

Citation:

Lovich, J. E., Ennen, J. R., Agha, M., & Gibbons, J. W. (2018). Where Have All the Turtles Gone, and Why Does It Matter?. BioScience, biy095, https://doi.org/10.1093/biosci/biy095

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