Sea turtles are ancient marine reptiles that have navigated the world’s oceans for over 100 million years. These widespread creatures inhabit tropical and temperate waters across the globe. Their survival is linked to highly specialized diets, which vary dramatically across the different species. This dietary specialization drives their behavior, migration patterns, and unique physical structures.
Species-Specific Menu
The diets of adult sea turtles are diverse, with each of the seven species having evolved to consume a particular type of marine food source. Green sea turtles are almost exclusively herbivorous, grazing primarily on seagrasses and algae in shallow coastal areas. By consistently cropping these plants, they help maintain the health and productivity of the seagrass meadows they inhabit.
Loggerhead sea turtles are carnivores that specialize in hard-shelled prey found on the ocean floor. Their diet includes bottom-dwelling invertebrates such as crabs, horseshoe crabs, and various mollusks like conchs and whelks. Kemp’s ridley and olive ridley sea turtles are more omnivorous, though their adult diets still center on the seabed, consuming crustaceans, fish, and mollusks. The Kemp’s ridley relies heavily on crabs, while the olive ridley has a broader menu that can include sea urchins and jellies.
Hawksbill sea turtles are “spongivores,” feeding exclusively on sea sponges found on coral reefs. This is an unusual diet, as sponges contain sharp, indigestible glass spicules and toxic chemicals, but the hawksbill’s digestive system can neutralize these defenses. Leatherback sea turtles, the largest of all sea turtles, are specialized “gelatinivores” whose diet consists almost entirely of soft-bodied plankton, primarily jellyfish and sea squirts. They must consume large amounts of this low-nutritional-value prey to sustain their large bodies.
Physical Adaptations for Foraging
The diet of each species is reflected in the specialized morphology of its mouth and jaw, which lack true teeth. Loggerhead and Kemp’s ridley turtles possess massive heads and powerful jaw muscles that support a strong beak. This robust structure and the bony plates inside the mouth are adapted for crushing the rigid exoskeletons of crabs and the shells of mollusks.
The hawksbill turtle has a narrow, pointed beak that resembles a bird’s beak, which allows it to reach into small crevices on coral reefs to extract sponges and other organisms. Green sea turtles have a finely serrated, saw-like beak, which functions like a pair of shears to scrape algae off rocks and tear through tough seagrass blades.
The leatherback turtle exhibits specialized adaptations for its gelatinous diet. It has delicate, scissor-like jaws with two sharp cusps that can pierce and hold onto slippery prey. The interior of its mouth and esophagus is lined with hundreds of stiff, backward-pointing spines called papillae. These papillae ensure that once a jellyfish is captured, it is guided toward the stomach while excess seawater is expelled, preventing the prey from washing back out.
Dietary Changes Over a Lifetime
A sea turtle’s diet changes as it grows from a hatchling to an adult. After emerging from the nest, hatchlings enter a phase known as the “lost years,” where they are carried by ocean currents in the pelagic zone. During this time, they are opportunistic omnivores, feeding on a mix of small organisms associated with floating seaweed mats, such as Sargassum, including plankton, small crustaceans, and fish eggs.
As juvenile turtles grow, they eventually recruit to coastal habitats, which triggers a shift in their feeding strategy and adult diet. For instance, juvenile green turtles start as omnivores but gradually transition to their adult herbivorous diet once they settle into nearshore seagrass beds. This transition from a carnivorous/omnivorous juvenile phase in the open ocean to a specialized adult diet in coastal areas is a common pattern across many sea turtle species.
Human Impacts on Foraging and Diet
The specialized foraging habits of sea turtles make them vulnerable to human-caused threats. Plastic pollution represents a danger, especially for the gelatinivores like the leatherback turtle. Floating plastic bags often closely resemble jellyfish, leading leatherbacks to ingest the debris, which can cause fatal blockages in the digestive tract. Even species with different diets, like the green turtle, will consume plastic that visually or chemically resembles algae and seagrass.
Ingesting plastic is fatal, as sharp fragments can puncture internal organs, and the material can create a false sense of fullness, leading to starvation. The foraging habitats themselves face degradation due to human activity. Coastal development and pollution contribute to the destruction of coral reefs, which provide the sponges for hawksbills, and the loss of seagrass meadows, the primary food source for green turtles. This loss of foraging grounds limits the food available, creating competition and forcing turtles to expend more energy to find sustenance.