LIFE CYCLE OF SEA TURTLES
Knowledge Series
Sea turtles undergo ontogenetic shifts, or shifts in the habitat that occur during the life cycle that responds to changes in vital rates. 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.
HATCHLINGS
Sea turtles do not provide parental care to the hatchlings thus the flexible semi-permeable eggshell, associated membranes, albumen, and secrete mucus during oviposition are the only protection received by the eggs. The nesting beach is the incubator for hatchlings’ embryonic development. Nest conditions determine embryonic survival and the success of the clutch. During incubation, energy stored in the egg by the mother is transformed into embryonic tissue by growing from a few cells at the beginning into a hatchling. The nest micro environment affects hatching and emergence success, sex ratios, morphology, and locomotion performance of the hatchlings.
Turtle nests incubate for variable periods of time, and length of the incubation period is inversely related to nest temperature. Incubation periods shortened as the temperature and amount of sunlight increased Incubation of embryos generates metabolic heat which causes the temperature of the nest to typically increase above surrounding sand temperature towards the final stage of incubation.
When the incubation period is over, the eggs that successfully developed pip will hatch within a few hours or days of each other. The first few hatchlings to hatch will wait for most of their siblings to break free from their eggs before digging upwards, this is called synchronous hatching. 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. These immature turtles, with a curved carapace length of 35-40cm, were originally termed “yearlings”, which posed a huge challenge to the understanding of sea turtle biology.
THE LOST YEARS
The young juveniles would remain pelagic for a period of time at a location that varies according to species. Scientists know very little of this phase before they appear again near shallow waters. Hence, the “lost years”. They reach sexual maturity around 20-30 years of age. Sea turtles only come to land to lay eggs. They lay eggs at the same beach where they were born. Some females lay eggs up to the age of 80.
NESTING
Sea turtles spend some time on land, where the time spent is affected by a few factors such as the reproductive readiness of the turtle, density of nesters, compactness of sand, and nesting experience of the turtle. The nests of the sea turtles are incubated to avoid predation. During incubation, the sex of the sea turtles can be affected by temperature.
Sea turtles spend most of their lives in the sea, but come to land to nest. Nesting turtles will come to the beach to nest, and the hatchlings will be incubated in a chamber. The temperature during incubation could determine the sex of hatchlings. Temperature-dependent sex determination of TSD in turtles was first identified among loggerhead turtles. Researchers then found that all sea turtle hatchlings adopt TSD. Cooler incubation temperatures were observed to produce more male hatchlings and warmer incubation temperatures produce more female hatchlings.
Temperature-dependent Sex Determination
Nest site selection shows temperature-dependent sex determination (TSD, also called environmental sex determination, or ESD), with females being produced at high temperatures and males being produced at low temperatures. The sensitivity of embryos leaves sea turtles shifts in the nesting environment. The pivotal temperature (Tpiv; i.e. that producing a 50:50 sex ratio) is very close to 29°C for widely separated populations and for different species of sea turtle. The thermal tolerance range (TTR) for development of sea turtle embryos incubated at constant temperature appears to fall between about 25 to 27°C and 33 to 35°C and is around 10 °C wide. The sensitive period for sex determination appears to occur around the middle third of incubation.
Continue Learning
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.
Biology
Sea turtles are marine reptiles that are found in tropical and subtropical seas in the world. Four sea turtles which have been found in Malaysia are; the green turtles, the hawksbill, the olive ridley and the leatherback. The green sea turtles …
“The Turtle’s teachings are so beautiful. So very special.
It teaches us that everything you are, everything you need and
everything you bring to the world is inside you”
Eileen Anglin
On Behalf Of All The Sea Turtles & Future Generations That Will Benefit From Your Generosity,
We Thank You In Advance For Your Support