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Sea turtle
Temporal range

Early cretaceous-Neurogene

110-0Ma

Sea turtle 2
An olive Ridley sea turtle is species of the sea turtle superfamily.
Conservation status Endangered
Kingdom Animalia
Phylum Chordata
Class Reptilia
Order Testudines(=Chelonii)
Clade Panchelonioidea
Superfamily Chelonioidea
Type species Testudo mydas
Families

Pancheloniidae

Heranodae

Takoubae

Zazaeroniidae

Cheloniidae

Pandermochelys

Dermochelyidae

Protostegidae

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Taxonomy and evolutionEdit

Sea turtles, along with other turtles and tortoises, are part of the order Testudines.

The seven living species of sea turtles are: flatback sea turtlegreen sea turtlehawksbill sea turtleKemp's ridley sea turtle,leatherback sea turtleloggerhead sea turtle and olive ridley sea turtle.[4] All species except the leatherback are in the family Cheloniidae. The leatherback belongs to the family Dermochelyidae and is its only member.

The species are primarily distinguished by their anatomy: for instance, the prefrontal scales on the head, the number of and shape ofscutes on the carapace, and the type of inframarginal scutes on the plastron. The leatherback is the only sea turtle that does not have a hard shell; instead, it bears a mosaic of bony plates beneath its leathery skin. It is the largest sea turtle, measuring 6 to 7 feet (1.8 to 2.1 m) in length at maturity, and 3 to 5 feet (0.91 to 1.52 m) in width, weighing up to 1,300 pounds (590 kg). Other species are smaller, being mostly 2 to 4 feet (0.61 to 1.22 m) and proportionally narrower.[5][not in citation given]

Sea turtles constitute a single radiation that became distinct from all other turtles at least 110 million years ago.

Family Cheloniidae

    • ===Cladogram[edit]===

Below is a cladogram showing the phylogenetic relationships of living and extinct sea turtles in the Chelonioidea based on Peer and Lee (2005)[6]

Phylogenetic relations of living and extinct chelonioid species
Panchelonioidea

Toxochelys

Ctenochelys

Chelonioidea
Pancheloniidae

Euclastes

Puppigerus

Cheloniidae

Pandermochelys

Protostegidae

Dermochelyidae

DistributionEdit

The superfamily Chelonioidea has a world-wide distribution; sea turtles can be found in all oceans except for the polar regions. Some species travel between oceans. The flatback sea turtle is found solely on the northern coast of AustraliaKemp's ridley sea turtle is found solely in the Gulf of Mexico and along the East Coast of the United States[7][1] [2]An Olive ridley turtle nesting on Escobilla Beach, OaxacaMexico ==Behavior and ecology==

HabitatEdit

Sea turtles are generally found in the waters over continental shelves. After taking to the water for the first time, males will not return to shore again.[5] During the first three to five years of life, sea turtles spend most time in the pelagic zone floating in seaweed beds. Green sea turtles in particular are often found in Sargassum beds, a brown seaweed in which they find shelter and food.[8] Once the sea turtle has reached adulthood it moves closer to the shore.[9] Females will come ashore to lay their eggs on sandy beaches during the nesting season.[5]

[3][4]A green sea turtle breaks the surface to breathe.===Respiration[edit]===

Sea turtles are almost always submerged, and, therefore, have developed an anaerobic system of energy metabolism. Although all sea turtles breathe air, under dire circumstances they may divert to anaerobic metabolism for long periods of time. When surfacing to breathe, a sea turtle can quickly refill its lungs with a single explosive exhalation and rapid inhalation. Their large lungs have adapted to permit rapid exchange of oxygen and to avoid trapping gases during deep dives.

Life CycleEdit

It takes decades for sea turtles to reach sexual maturity. After mating at sea, adult female sea turtles return to land to nest at night. Different species of sea turtles exhibit various levels of philopatry. In the extreme case, females return to the beach where they hatched. This can take place every two to four years in maturity. They make from one to eight nests per season. The mature nesting female hauls herself onto the beach, nearly always at night, and finds suitable sand on which to create a nest. Using her hind flippers, she digs a circular hole 40 to 50 centimetres (16 to 20 in) deep. After the hole is dug, the female then starts filling the nest with a clutch of soft-shelled eggs one by one until she has deposited around 50 to 200 eggs, depending on the species. Some species have been reported to lay 250 eggs, such as the hawksbill. After laying, she re-fills the nest with sand, re-sculpting and smoothing the surface until it is relatively undetectable visually. The whole process takes thirty to sixty minutes. She then returns to the ocean, leaving the eggs untended.[10]

[5][6]Turtle gender depends on sand temperature while the egg is incubating.

The hatchling's gender depends on the sand temperature.[11][12][13][14][15] Lighter sands maintain higher temperatures, which decreases incubation time and results in more female hatchlings.

It takes several decades for adult sea turtles to reach sexual maturity. The mature turtles migrate, sometimes for thousands of miles, to reach breeding sites. Male and female turtles mate in the water, and the males return to deep sea to feed. For several weeks, female sea turtles alternate between mating in the water and laying their eggs on land. Before laying her eggs, a female turtle will dig a hole in the sand with her hind flippers. She covers it with sand and returns to the ocean. About two months pass for the eggs to incubate under the sand. Afterwards, the eggs hatch, generally at night to avoid predation, and the hatchlings crawl to the water. They then swim out to sea to begin their own cycle of maturing and reproducing. Sea turtles can continue this cycle until they are 80 years old.[citation needed]

[7][8]1. Male and female turtles age in the ocean and migrate to shallow coastal water. 2. Turtles mate in the water near offshore nesting sites. 3. The adult male turtles return to the feeding sites in the water. 4. Female turtles cycle between mating and nesting, making between 1 and 8 nests a per season. 5. Females lay their eggs, often between 50 and 200 at a time. 6. When the season is over, female turtles return to feeding sites. 7. Baby turtles mature for 60-80 days and hatch. 8. Newly hatched turtles emerge from nests and travel from the shore to the water, usually at night. 9. Baby turtles mature in the ocean until they are ready to begin the cycle again.

Incubation takes about two months. The eggs in one nest hatch together over a very short period of time. When ready, hatchlings tear their shells apart with their snout and dig through the sand. Again, this usually takes place at night. Once they reach the surface, they instinctively head towards the sea. If, as happens on rare occasions, hatching takes place during daylight, only a very small proportion of each hatch succeed (usually 1%)[citation needed], because local opportunist predators, such as the common seagull, gorge on the new sea turtles. Thus there is an obvious evolutionary drive to hatch at night, when survival rates on the beach are much higher.

The hatchlings then proceed into the ocean, where a variety of marine predators await them. In 1987, Carr discovered that the young of Chelonia mydas and Caretta caretta spent a great deal of their pelagic lives in floating sargassum beds, where there are thick mats of unanchored seaweed. Within these beds, they found ample shelter and food. In the absence of sargassum beds, sea turtle young feed in the vicinity of upwelling "fronts".[8] In 2007, Reich determined that green sea turtle hatchlings spend the first three to five years of their lives in pelagic waters. In the open ocean, pre-juveniles of this particular species were found to feed on zooplankton and smaller nekton before they are recruited into inshore seagrass meadows as obligate herbivores.[9][16]

Instead of nesting individually like the other species, Ridley sea turtles come ashore en masse, known as an "arribada" (arrival). With the Kemp's ridley sea turtles this occurs during the day.

DietEdit

Sea turtles feed on a wide range of animals and plants. They are mostly omnivorous in their adult life, except the green sea turtle which is herbivorous, changing from a carnivorous diet when young. Some species specialise on certain prey;sea sponges are the principal food of hawksbill sea turtles, constituting 70–95% of their diets in the Caribbean.[17]Leatherback turtles feed almost exclusively on jellyfish and help control jellyfish populations.[18][19]

Aside from sponges, hawksbills also feed on algae and cnidarians (including the Portuguese man o' war), comb jellies and other jellyfish and sea anemones.[20] Green sea turtles are commonly found in seagrass meadows closer inshore as herbivorous grazers. The flatback turtle eats a variety of organisms such as seagrass, marine invertebrates includingmolluscs, jellyfish and shrimp and also fishes. It also consumes of soft coralsea cucumbers and other soft-bodied creatures.[21] The loggerhead sea turtle is omnivorous, feeding mainly on bottom-dwelling invertebrates, such as gastropodsbivalves, and decapods. The loggerhead has a greater list of known prey than any other sea turtle. Other food items include sponges, corals, sea penspolychaete wormssea anemonescephalopods, barnacles, brachiopodsisopods, insects, bryozoanssea urchinssand dollarssea cucumbers,starfish, fish (eggs, juveniles, and adults), hatchling turtles (including members of its own species), algae, and vascular plants.[22] During migration through the open sea, loggerheads eat jellyfish, floating molluscs, floating egg clusters, squid, and flying fish.[23] The Kemp's ridley turtle feeds on molluscs, crustaceans, jellyfish, algae or seaweed, and sea urchins. The olive ridley turtle is predominantly carnivorous, especially in immature stages of the life cycle. Animal prey consists of protochordates or invertebrates, which can be caught in shallow marine waters or estuarine habitats. Common prey items include jellyfish, tunicates, sea urchins, bryozoans, bivalves, snails, shrimp, crabs, rock lobsters, and sipunculidworms.[24] Aside from jellyfish, leatherbacks also feed on other soft-bodied organisms, such as tunicates and cephalopods.[25]

Salt glandEdit

Marine vertebrates maintain a balance of dissolved solutes and water in the body fluids by excreting excess salt ions.[26] Like other marine reptiles, sea turtles rely on a specialized gland to rid the body of excess salt ions, because reptilian kidneys can not produce urine with a higher ion concentration than sea water.[27] All species of sea turtles have a lachrymal salt gland in the orbital cavity, capable of producing tears with a higher salt concentration than sea water.[28]

Leatherbacks face an increased osmotic challenge compared to other species of sea turtle, since their primary prey are jellyfish and other gelatinous plankton, whose fluids have the same concentration of salts as sea water. The much larger lachrymal salt gland found in leatherbacks may have evolved to cope with the higher intake of salts from their prey. A constant output of concentrated salty tears may be required to balance the input of salts from regular feeding, even considering leatherback tears can have a salt ion concentration almost twice that of other species of marine turtle.[29]

Hatchlings depend on drinking sea water immediately upon entering the ocean to replenish water lost during the hatching process. Salt gland functioning begins quickly after hatching, so that the young turtles can establish ion and water balance soon after entering the ocean. Survival and physiological performance hinge on immediate and efficient hydration following emergence from the nest.[27]

Commensalism with barnaclesEdit

[9][10]Immature Hawaiian green sea turtle in shallow waters

Sea Turtles are believed to have a commensal relationship with some barnacles, in which the barnacles benefit from growing on turtles without harming them. Barnacles are small, hard shelled crustaceans found attached to multiple different substrates below or just above the ocean. The adult barnacle is a sessile organism, however in its larval stage it is planktonic and can move about the water column. The larval stage chooses where to settle and ultimately the habitat for its full adult life, which is typically between 5 to 10 years. A favorite settlement for barnacle larvae is the shell or skin around the neck of sea turtles. The larvae glue themselves to the chosen spot, a thin layer of flesh is wrapped around them and a shell is secreted. Many species of barnacles can settle on any substrate, however some species of barnacles have an obligatory commensal relationship with specific animals, which makes finding a suitable location harder.[30] Around 29 species of “turtle barnacles” have been recorded. However it is not solely on sea turtles that barnacles can be found; other organisms also serve as barnacle’s settlements. These organisms include mollusks, whales, decapod crustaceans, manatees and several other groups related to these species.[31]

Sea turtle shells are an ideal habitat for adult barnacles for three reasons. Turtles tend to live long lives, around 50 years, so barnacles do not have to worry about host death. Secondly, barnacles are suspension feeders. Sea turtles spend most of their lives swimming and following ocean currents and as water runs along the back of the turtle’s shell it passes over the barnacles, providing an almost constant water flow and influx of food particles. Lastly, the long distances and inter ocean travel these sea turtles swim throughout their lifetime, offers the perfect mechanism for dispersal of barnacle larvae. Allowing the barnacle species to distribute themselves throughout global waters is a high fitness advantage of this commensalism.[32]

There are a few speculations however at the idea that this relationship is truly commensal. The barnacles are not parasitic to their hosts but have been found to have negative effects to the turtles on which they choose to reside. These effects however seem to depend on the quantity of barnacles affixed to its back. The barnacles add extra weight to the sea turtle, potentially increasing the energy it needs for swimming and affecting its ability to capture prey.[33]

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