There are many different types of sea turtles, but the green sea turtle is one of the only species that is an herbivore. Green sea turtles feed on mollusks, crustaceans, and fish eggs as hatchlings, and then move on to algae and squid as adults. The leatherback sea turtle, on the other hand, is a carnivore, feeding mostly on jellyfish and other jellyfish-like invertebrates.
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Evolution
Sea turtles are members of a specialized food web. They have evolved different diets several times in their evolutionary history. Some species are carnivorous, like hawksbill turtles. Others are omnivorous, such as green sea turtles, which eat sea grass and algae.
They are able to navigate their food web by utilizing different resources at different times of the year. When they are close to shore, turtles use magnetic orientation and visual cues to find food. In the open ocean, they use wave and magnetic signals to navigate. Hatchlings are highly mobile, and must swim quickly to survive. This requires an intense diet, because they survive on a yolk sac that fuels them for only three days. Once their energy is depleted, they feed on small animals found in seaweed.
Diet
Sea turtles are part of the testudines suborder of reptiles. There are seven different species, including green, flatback, hawksbill, leatherback, loggerhead, olive ridley, and Kemp’s ridley. They can be quite large and are found around the world.
The diet of sea turtles varies considerably depending on their habitat. Some of the species are omnivores, while others are strictly herbivores. For instance, the green sea turtle mainly eats algae and seagrass, while the leatherback eats jellyfish, fish, and other soft-bodied invertebrates.
Predators
Rats are the first predators to appear around a sea turtle nest after the eggs have been laid. Rats from Orchid Island will scavenge the eggs on the surface and are wary of digging into the nest. Kukri snakes also frequent nests within 0.5 h of eggs being laid.
Many other animals hunt turtles as well. Sharks hunt not only other turtles, but fish, crabs, birds, and even other sharks. However, sharks are particularly dangerous to sea turtles. Their razor-sharp teeth are capable of breaking through their shells.
Reproductive behaviour
Sea turtles have a complex reproductive system and have a highly polygamous lifestyle. Males and females may mate multiple times throughout their lifetime and during each nesting season. As a result, a clutch of turtle eggs may have multiple fathers. While this behaviour may seem odd, it has important ecological implications for the health of the species.
A study of a wild population of green turtles in northern Cyprus revealed a female-biased primary sex ratio. The researchers studied tissue samples from twenty nesting females, representing 91% of all nests during the breeding season of 2008. The females produced as many as 23 offspring per clutch. The researchers estimated the sex of offspring from their incubation times.
Ecology
A comprehensive understanding of the trophic status of sea turtles can provide clues to the functioning of coastal ecosystems. Their trophic status influences their demography and reproductive output, and it may be the basis for understanding how they impact the ecosystem. Further, it may provide context for the abundance of nesting turtle populations.
This study employed bulk tissue isotope analysis to examine the green sea turtle’s niche and trophic position. The results showed that denitrification is associated with elevated values of d15N in benthic macroalgae. This result is consistent with studies of denitrification across ocean basins.
Conservation
Conservation of sea turtles requires a strong effort to balance the needs of the turtles and their surrounding ecosystem. This isn’t an easy task, but with the right effort, the efforts can yield positive results. Conservation efforts can involve long-term monitoring, education of the public, and policy initiatives.
In addition to habitat loss, threats to sea turtles include human activity and pollution. The two types of threats affect turtles’ habitat and migratory routes. Human development, for example, destroys sea turtle nesting grounds, pollutes them with agricultural effluent, and disturbs turtles and their young. Other threats include diseases such as fibropapillomatosis, an infectious tumor.
