BIOLOGY OF SEA TURTLES
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SPECIES
Sea turtles are marine reptiles that are found in tropical and subtropical seas around the world. There are a total of seven species of extant marine turtles. The four sea turtles which have been found in Malaysia are; green turtles (Chelonia mydas), hawksbill (Eretmochelys imbricata), olive ridley (Lepidochelys olivacea), leatherback (Dermochelys coriacea). Cheloniids are recognized by the light and low shell which are covered with scutes. The leatherback is known for its leathery skin and teardrop shaped carapace without epidermal scutes. The green sea turtles can grow up to 1.2m long and weigh in average 190kg. Their front flippers are longer than the back flippers. The carapace of an adult is brown in color with marble patterns and average of 1m in length.
Sea turtles have adapted physically to be able to move in water easily. They use their front flippers to swim and the back as rudders. Once in a while, they have to surface to take a breath and are able to stay under water up to an hour depending on their activity. They are often spotted around reefs foraging or resting.
DIET
These ancient marine reptiles have existed on Earth for over a 100 million years. Each of the different species of sea turtles have a different diet. The green turtles prefer to feed on seagrasses while the hawksbill, leatherback and olive ridley prefers invertebrates or soft-bodied organisms. The diets of sea turtles will also shift at least once in the life cycle of juvenile sea turtles. This takes place when the juvenile sea turtles go through a habitat shift, where they switch from a pelagic habitat and epipelagic feeding to a neritic habitat accompanied with benthic feeding.
As for green sea turtles, they will experience a diet shift from being omnivorous to herbivorous. Due to habitat shift, green turtles which once fed on pelagic organisms in pelagic habitat will feed on seagrasses in benthic habitats. Hawksbill turtles have a more omnivorous diet, consuming large quantities of vegetation such as Sargassum, Rhizophora, Cymodocea, other algae and benthic invertebrates such as sponges. Adult olive ridleys forage in deep water, shallow benthic waters and sometimes in estuaries. Jellyfish, crabs, algae and bryozoans are the major constituents of food they feed on.
Leatherback turtles, which are believed to be the most pelagic in comparison to all sea turtles, spend most of their lives in the open ocean. Leatherbacks do not experience a diet shift between size classes in comparison to the other turtle species as they are able to capture and consume gelatinous prey species independent of their sizes. Leatherbacks consume a lot of scyphomedusae and pelagic tunicates.
REPRODUCTION
Like most reptiles, sea turtles breed seasonally. Courtship activity usually occurs near the nesting beach. One female may mate with several males. During inter-nesting periods, sea turtles will show weight gain while they prepare clutches to lay eggs. However during the nesting season, sea turtles go through a fasting period due to limited abundance of food and to conserve energy. Mass nesting behaviour, or arribadas are only observed among olive ridley turtles.
As for the other sea turtles, year-round nesting was recorded. The nesting sea sonality was found to be influenced by the ability of the sea turtles to find a mate, the suitability of the nesting beach for incubation and to allow safe dispersion of hatchlings once they emerged.
The surviving hatchlings later enter the ocean and infrequently seen again until they reappear in shallow coastal habitats as immature adults to become permanent or semi-permanent residents. Declining reproductive success is influenced by an increased level of contaminants across foraging areas and nesting beaches. The contaminants were found to affect the physiological processes of the sea turtles.
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Life Cycle
The general life cycle starts from the adult females that dig nest cavities on sandy, ocean-facing beaches. After the incubation, the hatchlings emerge from the nests, crawl to the water and swim out to the open ocean.
Ecology
Sea turtles are highly migratory marine reptiles that play vital roles in maintaining the health of the oceans. All sea turtles use different habitats and areas during their life cycle such as the seagrasses and the coral reefs.
Protection
According to the IUCN Red List the olive ridley are globally vulnerable while hawksbills on the other hand are critically endangered. In Malaysia, among the four species that have been sighted, only green sea turtles have a fairly stable population.
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