Sea turtles inhabit all the oceans of the world except the Arctic, and they therefore have a broad range of habitats and diets. Each species has uniquely evolved to different environments and available food . Some are nomadic marathon swimmers and others call coral reefs their home. There are seven species of sea turtles found globally. So, who eats what and what does a sea turtle diet consist of?
An Eggcellent Start
All sea turtles start out life as eggs. Female turtles dig nests deep in the ground and lay clutches containing many eggs. Energy from the female turtle is stored as the egg yolk. This allows a sea turtle to fully develop from just a few cells to a fully formed independent hatchling .
Aside from the vital energy provided by the yolk, eggs also exchange heat, water, oxygen and carbon dioxide with other eggs and the surrounding sand .
The composition of the egg yolk is directly affected by the diet of the mother turtle . Not only does the mother influence the nutritional content of her eggs, but she can also pass on unnatural chemicals and pollutants.
Human activity has led to harmful pollutants, like pesticides, being taken up by foraging turtles and passed on to their eggs .
Sea Turtle Diet By Species
Green Turtle Diet: From Carnivore to Herbivour
Green turtles begin their life living in open ocean near the surface. They start out with a generally carnivorous diet for the first 3-5 years, which can include zooplankton, mollusks, and crustaceans. 
As they grow, juvenile green turtles move to coastal waters and reefs and shift to a more herbivorous diet. Juvenile greens eat mainly seagrasses and algae , however, their diet can also include a number of invertebrate species such as jellyfish and sponges. .
As adults, green turtles have a unique “vegetarian” diet. Adult green turtles live in shallower waters with a primarily herbivorous diet, thriving on sea grass.  Just like cows grazing on terrestrial pastures, adult greens are going to ingest the occasional invertebrate together with the seagrass by accident.
Hawksbill Turtle Diet: Mostly Spongy
Juvenile and adult hawksbill turtles live and thrive on coral reefs, primarily eating sponges . While hawksbill turtles in the Caribbean live nearly exclusively of sponges, their Indian Ocean cousins feast on a wider range of organisms also including corals, sea urchins and jellyfish in their diet .
Leatherback Diet: All About Jellyfish
Leatherback turtles swim great distances, live in open ocean and primarily feed on jellyfish. In addition to true jellyfish, leatherback turtles have been reported to feed on other soft bodied organisms (pyrosomes and siphonophores) as well as squid and octopus. 
Olive Ridley Diet: All Eating
Adult olive ridleys tend to live in the open ocean with a broad omnivourous diet. Their diet includes crabs, mollusks, algae, jellyfish and shrimp . They are also known to eat fish, showing opportunistic feeding behaviour . Apart from the open ocean, olive ridley are also known to feed in shallower areas as “bottom feeders”, diving to feed on organisms living on the ocean floor .
Loggerhead Diet: True Carnivores
Loggerhead turtles are carnivores, feeding on a variety of prey depending on their life stage. 
Juvenile and adult loggerheads feed on a variety of crustaceans found on the ocean floor, including crabs, lobster and shrimp. They eat snails, mussels and even small amounts of sea grasses and algae . There has also been reports of opportunistic feeding on fish caught or discarded by fishermen .
Kemps Ridley Diet: Mostly Crustaceans
Kemps ridley turtles are only found in the Northwest Atlantic Ocean. Juvenile and adults primarily feed on crabs. They also eat other crustaceans and mollusks and occasionally fish – showing the ability to be opportunistic feeders. 
Flatback Diet: Soft Bodied Invertebrates
The Flatback sea turtle lives exclusively in Australia and little is known about the species and their diet throughout their lifetime. Juvenile and adult flatbacks are known to eat snails, jellyfish, corals and other soft bodied invertebrates.
How Does Sea Turtles’ Diets Affect The Ocean Ecosystems?
Sea turtles play a vital role in ocean ecosystems, affecting the diversity and function of ocean habitats . Here are just a few examples.
Green Sea Turtles Maintain Healthy Seagrass Beds
Green sea turtles are vital in maintaining healthy beds of seagrass. They prevent seagrass becoming overgrown and by grazing they even improve the quality and growth of the grass . Overgrown sea grass can decompose and develop a build up of algae, bacteria and fungus. The die-off of seagrass in Florida during the 1980s has been directly linked with the dramatic decline in green turtle populations .
Hawksbills Manage Sponges On Coral Reefs
Hawksbill turtles manage sponges on coral reefs. Sponges compete with corals for space on reefs and without predators they would quickly take over. Hawksbills are one of the few marine animals that can eat these toxic sponges, allowing corals to grow and thrive.
Sea Turtles Keep Jellyfish Populations Under Control
Several species of sea turtles, but particularly the leatherback, play a key role in managing jellyfish populations. A top jellyfish predator, the huge size of leatherbacks means they can consume up to 200kg of jellyfish a day! Jellyfish eat fish eggs and larvae and compete for fish food.  So a decline in leatherbacks could mean more jellyfish and fewer fish in our oceans. 
Bottom Feeders Improve Aeration On the Sea Bed
Loggerheads and other species that feed on crustaceans on the ocean floor increase rates of nutrient recycling by crushing shells during feeding . During their hunt for prey, loggerheads create trenches in the sea floor. By clearing sand they improve aeration and nutrient distribution on the sea bed, benefitting the ecosystem. 
What Sea Turtles Shouldn’t Eat
Sea turtles have survived for millions of years and each species has adapted to different diets. Through the natural abundance of the ocean, they have flourished in various habitats and available food sources. As we have just learnt, they also play key roles in a healthy marine ecosystem.
However, a new threat has emerged in the last few decades. A previously unknown material to marine life, plastic now pollutes our oceans . Sea turtles around the world are ingesting plastic with devastating consequences. Plastic can cause blockages in the gut, malnutrition and death . Globally, estimates of around 52% of all sea turtles have ingested plastic . In some areas this estimate is even higher! For example, in a study off the coast of Brazil, turtles accidentally caught in fishing nets were examined and an astonishing 90% of juvenile green turtles were found to have ingested plastic .
Sea turtles ingest plastic most likely because they confuse the artificial material with actual food items. A plastic bag floating in the ocean can easily be mistaken for a jellyfish.If we want to protect sea turtles, and through them our oceans at large, we again have to rethink our plastic consumption and waste production.
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Got More Sea Turtle Questions?
Sea Turtles FAQ – The Answers to All Your Sea Turtle Questions
Sea turtles can hold their breath for several hours, depending on their level of activity.
If they are sleeping, they can remain underwater for several hours. In cold water during winter, when they are effectively hibernating, they can hold their breath for up to 7 hours. This involves very little movement.
Although turtles can hold their breath for 45 minutes to one hour during routine activity, they normally dive for 4-5 minutes and surfaces to breathe for a few seconds in between dives.
However, a stressed turtle, entangled in a ghost net for instance, quickly uses up oxygen stored within its body and may drown within minutes if it cannot reach the surface.
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- Hays GC, Hochscheid S, Broderick AC, Godley BJ & Metcalfe JD 2000. Diving behaviour of green turtles: dive depth, dive duration and activity levels. Marine Ecology Progress Series 208: 297-298.
- Hochscheid S, Bentivegna F & Hays GC 2005. First records of dive durations for a hibernating sea turtle. Biology Letters 1: 82-86.
- Lutz PL and Musik JA (eds.) 1996. The Biology of Sea Turtles Volume I. CRC Press.
The actual documentation of a sea turtle’s age in the wild is difficult or nearly impossible. Individual turtles can be tracked for a shorter time of six month to three years with the help of satellite transmitters. Longterm studies rely on capture-recapture principle, just like our turtle photo id project. Each photo of a turtle represents a recapture event documenting that the individual is still alive.
A study of nesting green turtles in Hawaii observed female turtles returning to nest for up to 38 years after they were first identified. Assuming the average age at first nesting activity of 24 years, this would show that green turtles can live to up to at least 62 years.
Similar estimates have been made for loggerhead turtles.
- Dodd C 1988. Synopsis of the biological data on the loggerhead sea turtle. Ecology 88.
- Humburg IH and Balazs GH 2014. Forty Years of Research: Recovery Records of Green Turtles Observed or Originally Tagged at French Frigate Shoals in Northwestern Hawaiian Islands, 1973-2013. NOAA Technical Memorandum NMFS-PIFSC-40.
When sea turtles are juveniles, it is very difficult to tell their sex by eye as they do not differ externally. However, after reaching sexual maturity male sea turtles develop a long tail, which houses the reproductive organ. The tail may extend past the hind flippers.
Female turtles have a short tail, which generally doesn’t extend more than 10 cm (4 inches) past the edge of the carapace. Male sea turtles (except leatherbacks) have elongated, curved claws on their front flippers to help them grasp the female when mating.
The sex of a sea turtle embryo is determined by the temperature of the sand: warm temperatures result in more females while cooler temperatures result in more males.
The olive and kemp’s ridley sea turtles are the smallest species, growing only to about 70 cm (just over 2 feet) in shell length and weighing up to 45 kg (100 lbs). Leatherbacks are the largest sea turtles. On average leatherbacks measure 1.5 – 2m (4-6 ft) long and weigh 300 – 500 kg (660 to 1,100 lbs). The largest leatherback ever recorded was 2,56 m (8.4 ft) long and weighed 916 kg (2,019 lbs) !
55.6-66.0 cm carapace length, weight range of 25-54 kg for nesting females.
- Marquez-M R 1994. Synopsis of Biological Data on the Kemp’s Ridley Turtle, Lepidochelys kempi (Garman, 1880). NOAA Technical Memorandum NMFS-SEFSC-343.
Curved carapace length 52.5-80.0 cm, weight less than 50 kg (average 35.7 kg) for nesting females.
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- Reichart HA 1993. Synopsis of biological data on the olive ridley sea turtle Lepidochelys olivacea (Eschscholtz 1829) in the western Atlantic. NOAA Technical Memorandum NMFS-SEFSC-336.
Nesting females reported between 53.3 and 95.5 cm carapace length, with weight between 27.2 and 86.2 kg.
- Witzell WN 1983. Synopsis of biological data on the hawksbill turtle, Eretmochelys imbricata (Linnaeus, 1766). No. 137. Food & Agriculture Org.
Nesting green females reported curved carapace length 75-134 cm, weight (after egg deposition) 45-250 kg (!).
- Hirth HF 1997. Synopsis of the Biological Data on the Green Turtle Chelonia mydas (Linnaeus, 1758). Vol. 2. Fish and Wildlife Service, US Department of the Interior.
Ones study (Ref. 1) found nesting females have a mean curved carapace length 86.3 cm, and mean weight of 67.4 kg. Another study (Ref. 2) found flatbacks to be between 87.5-96.5 cm.
- Schäuble C, Kennett R and Winderlich S 2006. Flatback Turtle (Natator depressus) nesting at Field Island, Kakadu National Park, Northern Territory, Australia, 1990-2001. Chelonian Conservation and Biology 5: 188-194.
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The largest loggerhead was reported stranded in 1938 on the welsh coast (Tenby, Pembrokshire) with a carapace length of 146.7 cm. The turtle was highly emaciated and missing a front flipper. It was reported to weigh only 27.8 kg, which is severely underweight for a turtle of that size. On average nesting and therefore adult female loggerheads have a curved carapace length of 65.1-114.9 cm and weigh between 40.0 and 180.7 kg. Males fall into the same size range (79.0-104.0 cm curved carapace length).
- Brongersma LD 1972. European Atlantic turtles. Zoologische Verhandlingen 121, Leiden.
- Dodd C 1988. Synopsis of the biological data on the loggerhead sea turtle. Ecology 88: 1-119.
143.8-169.5 cm curved carapace length, weight 259-506 kg recorded for nesting females all around the world. Largest ever recorded specimen was found dead on a beach on the coast of Wales. The adult male turtle weighed 916 kg and its shell was 256.5 cm long. An autopsy revealed that it had drowned.
- Eckert KL and Luginbuhl C 1988. Death of a Giant. Marine Turtle Newsletter 43: 2-3.
- Eckert KL, Wallace BP, Frazier JG, Eckert SA and Pritchard PCH 2012. Synopsis of the Biological Data on the Leatherback Sea Turtle (Dermochelys coriacea). Biological Technical Publication BTP-R4015-2012, US Fish & Wildlife Service.
In the Maldives, the turtles we observe on the reefs show extremely high site fidelity, meaning they do not, in general, move from reef to reef to find food but have a “home reef”.
Upon reaching maturity most species travel long distances every few years for a breeding migration (from their feeding grounds to their breeding sites and back). These migrations can be hundreds or thousands of kilometers and take several months.
The leatherback turtle can travel 16,000 km (10,000 miles) or more each year, crossing the entire Pacific Ocean in search of jellyfish, while loggerheads have been tracked traveling from Japan to Baja, a distance of 13,000 km (8,000 miles). The longest recorded green turtle migration was 3,979 km (2,472 miles) from Chagos to Somalia.
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