The leatherback sea turtle, Dermochelys coriacea, is the largest sea turtle species. Adults can reach lengths of over six feet and weigh more than 1,400 pounds. Unlike its hard-shelled relatives, the leatherback has a flexible, leathery carapace supported by a mosaic of small bones beneath the skin. This structure allows for deeper dives and greater pressure tolerance. The animal is also one of the world’s most impressive migrants, traveling thousands of miles between tropical nesting beaches and colder feeding grounds. Their ability to maintain a relatively high core body temperature in frigid waters, a form of gigantothermy, enables them to occupy a vast global range.
The Specialized Jellyfish Diet
Leatherback turtles overwhelmingly feed on jellyfish and other soft-bodied gelatinous zooplankton, such as salps and pyrosomes. This specialized diet is central to the species’ survival, particularly for fueling its massive body and extensive migrations. Jellyfish are composed of up to 96% water and possess a very low caloric density compared to other marine prey. Because their primary food source offers so little energy, leatherbacks must consume enormous quantities daily to sustain their high metabolic rate.
A leatherback may need to eat the equivalent of up to 73% of its own body mass each day, which can translate to hundreds of pounds of jellyfish. This extreme consumption rate is necessary to maintain the turtle’s large body size and its unique capacity for gigantothermy, which allows it to forage in cold subpolar waters.
Anatomical Features for Soft Prey
To manage a diet of slippery, soft-bodied prey, the leatherback turtle possesses a highly specialized digestive tract. The most distinct feature is the lining of its entire esophagus, which is covered in hundreds of backward-pointing, spine-like structures called papillae. These papillae are keratinous projections that function like a one-way conveyor belt.
The sharp, pointed nature of the papillae serves two distinct purposes in the feeding process. First, they grip the gelatinous prey once it is swallowed, preventing the slippery jellyfish from being regurgitated or escaping back out of the mouth. Second, the papillae act as a protective barrier, shielding the turtle’s sensitive tissues from the stinging nematocysts of the jellyfish during ingestion. This unique anatomical adaptation ensures the efficient capture, processing, and retention of the leatherback’s primary food source.
Why Plastic Bags Pose a Deadly Threat
The leatherback’s reliance on gelatinous prey creates a direct and deadly vulnerability to plastic pollution. Floating plastic bags, balloons, and sheeting can closely resemble the appearance and movement of jellyfish in the water column, leading the turtles to mistake the debris for food. This visual confusion, coupled with their constant need to consume large volumes of prey, results in frequent ingestion of marine plastic.
Once a plastic bag is swallowed, the leatherback’s specialized papillae trap the indigestible material. The backward-facing spines prevent the turtle from regurgitating the plastic, cementing it within the digestive tract. This blockage in the esophagus or intestines prevents the proper uptake of nutrients and causes a false sense of fullness. The turtle starves, often with its stomach full of non-nutritive plastic debris. The species’ obligate diet and unique anatomy, which are evolutionary advantages for consuming jellyfish, tragically become liabilities in an ocean filled with human-made waste.