Sea turtles are ancient reptiles that have navigated Earth’s oceans for over 100 million years. Their survival depends on a complex food web that includes various plants and animals. If you want a quick answer, sea turtles are omnivores that eat seagrass, algae, jellyfish, mollusks, crustaceans, fish, and even eggs of other turtles.
This article will provide a comprehensive overview of the sea turtle food web, exploring what different species eat at various life stages from hatchlings to adults. We’ll also look at how sea turtle diets vary by habitat, as well as how their role as predators and prey helps maintain balance in marine ecosystems.
Sea Turtle Diet Basics
When it comes to what sea turtles eat, their diets actually change significantly as they grow and mature. The cute little hatchlings that scramble into the ocean have different dietary needs than the lumbering, majestic adults gliding through the seas.
Herbivorous Tendencies in Hatchlings
Newly hatched sea turtles are tiny little guys, often under 2 inches long. With their diminutive size comes a primary dependence on tiny drifting sea creatures like larval crabs, jellyfish, sponges, seaweed, and algae for sustenance.
Essentially, the baby turtles start out more herbivorous, subsisting mainly on floating marine plant matter during their first year of life.
Omnivorous Adaptations in Juveniles and Adults
As juvenile sea turtles grow larger and venture further out into the ocean waters, their diets shift to become more omnivorous in nature. Their longer digestive tracts and bigger mouths allow them to hunt and consume larger prey.
Adults turbocharge this adaptation to basically feast on anything they can capture and swallow.
The loggerhead sea turtle diet serves as a good example. Small bottom-dwelling invertebrates like conchs, clams, shrimp, crab, and worm-like creatures make up the bulk of their menu. The powerful jaws of these reptilian beasts also make snacking on shelled mollusks no problem.
As far as omnivorous tendencies go, loggerheads have also been observed hunting fish like mackerel and anchovies when the opportunity presents itself.
While adult green sea turtles munch mainly on seagrasses and algae, they balance it out with the occasional invertebrate protein power-up. Their asymmetrical jaw structure wields that veggie shredder on one side with a handy sinew cutting carnivore chopper on the other.
This evolutionary mashup gives them the ability to tear into flesh when needed.
The unmatched chill and patience of the giant leatherback sea turtle even allows it to feast on free-swimming jellyfish. As the jellied mass drifts by, the leatherback simply opens its mouth and sucks it in whole!
So in the end, the herbivorous hatchlings grow up to become adaptable omnivores and expert ocean survivors. They cruise the seas hunting a flexible mix of marine plants and animals that provides all the nutrition they require.
Their diverse palates are a true testament to the evolutionary diet dynamics on display in the fascinating world of the sea turtle!
Key Food Sources
Seagrasses and Algae
Seagrasses and algae are vital food sources for many species of sea turtles, especially green sea turtles. Green sea turtles are almost entirely herbivorous, feeding primarily on the seagrasses and algae that grow in shallow coastal waters.
Studies show that more than 60% of a green turtle’s diet consists of seagrasses such as Thalassia and Halodule species (Bjorndal 1997). Their specialized mouths allow them to efficiently clip and shred seagrass blades.
Green turtles also feed extensively on algae species such as Caulerpa, Ulva, and Codium.
Jellyfish and Ctenophores
Leatherback sea turtles prey almost exclusively on jellyfish and other gelatinous zooplankton such as ctenophores (also known as comb jellies). Their favorited prey are jellyfish from the classes Scyphozoa (Chrysaora, Aurelia species), Cubozoa (Chironex fleckeri), and Hydrozoa (Porpita, Velella, Physalia) (Heaslip et al.
2012). It’s estimated up to 60% of a leatherback’s diet consists of scyphomedusae jellyfish. Many scientists believe leatherbacks’ strong preference for jellyfish helps provide an ecological balance by controlling jellyfish populations.
Mollusks
Some sea turtle species feed heavily on mollusks, particularly bivalves and gastropods that live on the seafloor. Loggerhead turtles often forage for mollusks in addition to crustaceans and other benthic organisms.
Studies in the Mediterranean show mollusks can account for over 50% of the diet of some loggerheads in certain areas (Casale et al. 2008). The powerful jaws of loggerheads allow them crush thick mollusk shells to access the soft bodies inside.
Crustaceans
Crabs, shrimp, lobsters, and other crustaceans are important prey for loggerhead, olive ridley, hawksbill, and Kemp’s ridley sea turtles. Loggerheads feed on portunid crabs, stone crabs, and brine shrimp.
Studies show crustaceans can account for 20-40% of the diet of these species (Seney and Musick 2007). The smaller Kemp’s ridleys often feed on swimming crabs and shrimp found near ocean beaches. All species use their sturdy beaks and jaws to crush through crustacean shells and exoskeletons.
Fish
Although predominantly carnivorous, some sea turtle species do feed opportunistically on fish such as menhaden, mullet, wrasses, and parrotfish. Hawksbills, loggerheads, and occasionally greens and leatherbacks have been found with fish remains in their stomachs.
However, fish only make up a small percentage of most sea turtles’ diets. One study of Australian loggerheads showed fish accounted for just 3% of their total diet (Gulko and Eckert 2004). So while sea turtles may eat fish on occasion, they rely much more heavily on invertebrate prey.
Other
In addition to the main food sources described above, sea turtles will sometimes feed opportunistically on other prey items. Leatherbacks have been documented consuming floating seaweed and plastic debris which they mistake for jellyfish.
Loggerheads have been found with remains of marine angiosperms like eelgrass in their stomachs. Hawksbills will occasionally eat sponges and coral. And all species have been known to ingest tar balls, plastic, styrofoam, and marine debris—often by accident when they mistake them for food floating in the ocean (Schuyler et al.
2014).
Variation Between Species
Green Sea Turtles
Green sea turtles are named for the green color of their cartilage and fat, not their shells. As juveniles, they are carnivorous, but as adults, they become primarily herbivorous, feeding on sea grass and algae. Their powerful jaws help them to eat these tough plants.
Green sea turtles are found mainly in tropical and subtropical coastal waters around the world.
Hawksbill Sea Turtles
The hawksbill sea turtle gets its name from its narrow, pointed beak, resembling a hawk’s bill. They primarily eat sponges along coral reefs, using their narrow beaks to reach into crevices. Their critically endangered status is partly due to the demand for their shells to make tortoiseshell jewelry and other decorative items.
Hawksbills are found mainly in tropical, subtropical, and temperate oceans around the world.
Kemp’s Ridley Sea Turtles
Kemp’s ridley sea turtles are the world’s smallest and most endangered sea turtles. They feed primarily on crabs and other crustaceans near shore and in saltwater bays and estuaries. Their population was devastated in the mid-20th century from overharvesting of eggs and capture in fishing gear, though conservation efforts have helped numbers rebound somewhat.
Kemp’s ridleys nest mainly along the western Gulf of Mexico.
Leatherback Sea Turtles
The leatherback is the largest sea turtle and one of the most migratory, crossing both the Atlantic and Pacific Oceans. Their leathery, oil-filled carapace helps them withstand cold water temperatures during these lengthy migrations.
Leatherbacks feed almost exclusively on jellyfish and other soft-bodied invertebrates. Despite their massive size, they are very agile swimmers, which aids them in capturing these gelatinous prey.
Loggerhead Sea Turtles
As their name suggests, loggerhead sea turtles have very large heads and strong, powerful jaws to feed on hard-shelled mollusks and crustaceans like conchs, clams, and crabs. They utilize rocky reefs and coastal areas around the world, where they find many of these prey items.
Loggerheads occasionally eat jellyfish and vegetation as well. These turtles face threats from fishing nets, marine pollution, and loss of nesting habitat.
Olive Ridley Sea Turtles
Olive ridley sea turtles, as their name suggests, have olive-colored carapaces. They are best known for their unique synchronized mass nesting events where hundreds of females come ashore to lay eggs at the same time. Though the exact reason is unknown, it may help protect against predators.
Olive ridleys feed mainly on jellyfish, salps, crabs, and shrimp. Though abundant, they still face threats from egg and meat harvesting and becoming trapped in fishing gear.
Differences Between Habitats
Coastal Waters
Coastal waters provide an abundant habitat for sea turtles to find food. The shallow areas along coastlines contain seagrass beds and coral reefs which support diverse marine life. Common prey for sea turtles in these habitats include seagrasses, algae, jellyfish, crabs, mollusks, and small fish.
The nutrient-rich environment enables dense growth of seagrass and algae, which green sea turtles rely heavily upon. Meanwhile, hawksbill sea turtles feast on sponges found growing on coral reefs. The complex structures of the reef also provide hiding spaces for crabs and other crustaceans sought after by loggerhead turtles.
Overall, coastal zones contain a buffet of food options for different sea turtle species.
Coral Reefs
Coral reefs are a hotspot of biodiversity in the ocean, offering sea turtles abundant food sources. Sponges, jellyfish, crabs, shrimps, mollusks, and small fish thrive in these habitats. Hawksbill sea turtles in particular have a strong affinity for coral reefs, as their diet consists predominantly of sponges.
The nooks and crannies of the reef provide ample places for sponges to grow. These ancient turtles have even evolved a narrow pointed beak perfect for extracting sponges from the reef. Green sea turtles also frequent coral reefs to graze on the algae growing on the reef.
The rich diversity of life draws other sea turtle species to coral reefs as well in search of crabs, jellyfish, and fish to eat. The coral reef food web sustains sea turtles across various life stages.
Open Ocean
Though less productive than coastal zones, the open ocean still offers critical food sources for sea turtles. While underwater seagrass meadows and coral reefs are absent, floating mats of algae and sargassum provide habitat and food for some species.
Leatherback sea turtles specifically seek out these floating rafts to feed on jellyfish, salps, and other gelatinous creatures collected there. Open ocean predators like mahi mahi, tuna, and squid also follow these floating habitats.
Leatherbacks may opportunistically feed on these larger prey in the open ocean. Meanwhile, loggerhead sea turtles hunt for squid, mollusks, and crustaceans in the vast open water. Though the diversity is lower, sufficient food still exists to sustain migrating and foraging sea turtles in the open ocean habitat.
Role in the Marine Food Web
Prey for Sharks and Large Fish
Sea turtles play an integral part in marine food webs as both predator and prey. Young sea turtles feeding on jellyfish, mollusks and crustaceans serve as a food source for sharks and large predatory fish like groupers and snappers.
Loggerhead turtles in particular make up a significant portion of the diets of tiger sharks and other large predators in coastal habitats.
According to a 2010 study, the remains of loggerhead turtles were found in 38% of tiger shark stomachs examined in one region of the Northwest Atlantic. Their vulnerability as juveniles and subadults contributes to the endangerment of loggerheads and other sea turtle species preyed upon by sharks before reaching maturity and reproducing.
Help Control Jellyfish Populations
At the same time, sea turtles help regulate jellyfish populations through predation. Leatherback sea turtles consume hundreds of pounds of jellyfish daily, making them one of the foremost jellyfish predators in temperate and subtropical oceans.
This helps prevent overpopulation and dominance of jellyfish, which compete for food sources with commercially valuable fish species.
One study in the Irish Sea estimated that leatherbacks consume 61 million lion’s mane jellyfish annually. Remove leatherbacks, and jellyfish would dramatically increase, potentially decimating stocks of herring and other small prey fish.
So while sea turtles compete with humans for certain fish stocks, they also help maintain balance in marine ecosystems.
Transport Nutrients Between Ecosystems
Lastly, sea turtles serve a key function in transporting nutrients between terrestrial and marine ecosystems. As hatchlings emerge on beaches and quickly make their way to open ocean habitats with rich foraging grounds, they export significant nutrients from coastal ecosystems.
Meanwhile, adult sea turtles offload substantial nutrient loads on nesting beaches and in nearshore habitats through egg-laying and excretion. One Australian study found a single loggerhead turtle nest provides over 700 grams of nitrogen and phosphorus to beach ecosystems over the incubation period.
This influx of nutrients benefits beach vegetation and serves as an input to adjacent coastal food webs.
In these ways, sea turtles are far more than passive occupants of marine food chains. As both formidable predators and prey for a diverse range of species, they shape ecosystem dynamics and serve as conduits for nutrient exchange across habitat boundaries.
Conclusion
In conclusion, sea turtles fill an essential niche in ocean environments as omnivores that eat diverse prey at different life stages. Their flexible, opportunistic diets help regulate marine food webs by linking seagrass beds, coral reefs, and open ocean habitats.
Learning more about sea turtle eating habits provides insights into maintaining balance across interconnected coastal and pelagic ecosystems.
