Editing Sea turtle (section)

== Physiology ==

===Osmoregulation===

Sea turtles maintain an internal environment that is [[hypotonic]] to the ocean. To maintain hypotonicity they must excrete excess salt ions.<ref>{{cite journal |author1=Nicolson, S.W. |author2=P.L. Lutz |year=1989 |url=http://jeb.biologists.org/content/144/1/171.full.pdf |title=Salt gland function in the green sea turtle ''Chelonia mydas'' |journal=Journal of Experimental Biology |volume=144 |issue=1 |pages=171–184|doi=10.1242/jeb.144.1.171 |doi-access=free |bibcode=1989JExpB.144..171N }}</ref> Like other marine reptiles, sea turtles rely on a specialized gland to rid the body of excess salt, because reptilian kidneys cannot produce urine with a higher ion concentration than sea water.<ref name="ncbi">{{cite journal |author1=Reina RD |author2=Jones TT |author3=Spotila JR |title=Salt and water regulation by the leatherback sea turtle ''Dermochelys coriacea'' |journal=Journal of Experimental Biology |volume=205 |issue=13 |pages=1853–60 |date=July 2002  |doi=10.1242/jeb.205.13.1853 |pmid=12077161 |bibcode=2002JExpB.205.1853R |url=http://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=12077161|url-access=subscription }}</ref> All species of sea turtles have a [[lachrymal gland]] in the orbital cavity, capable of producing tears with a higher salt concentration than sea water.<ref>{{cite journal |author1=Schmidt-Nielsen K |author2=Fange R |year=1958 |title=Salt glands in marine reptiles |journal=Nature |volume=182 |issue=4638 |pages=783–5 |doi=10.1038/182783a0|bibcode=1958Natur.182..783S |s2cid=4290812 }}</ref>

Leatherback sea turtles 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 gland found in leatherback sea turtles 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 sea turtle tears can have a salt ion concentration almost twice that of other species of sea turtle.<ref>{{cite journal | last1 = Hudson | first1 = D.M. | last2 = Lutz | first2 = P.L. | year = 1986 | title = Salt gland function in the leatherback sea turtle, ''Dermochelys coriacea'' | journal = Copeia | volume = 1986 | issue = 1| pages = 247–249 | jstor=1444922 | doi=10.2307/1444922}}</ref>
[[Image:Young Honu-Kahala.png|thumb|Immature Hawaiian green sea turtle in shallow waters]]
[[File:Sea turtles bask in the Papahānaumokuākea Marine National Monument.png|thumb|Sea turtles basking in the [[Papahānaumokuākea Marine National Monument]] in the [[Northwestern Hawaiian Islands]].]]
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 sea 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.<ref name="ncbi" />

=== Thermoregulation ===
All sea turtles are [[poikilotherm]]s.<ref name=":30">{{cite journal|title = Feasibility of Using Sea Surface Temperature Imagery to Mitigate Cheloniid Sea Turtle – Fishery Interactions off the Coast of Northeastern USA|last1 = Braun-McNeill|first1 = Joanne|date = December 2008|journal = Endangered Species Research|doi = 10.3354/esr00145|last2 = Sasso|first2 = Christopher|last3 = Epperly|first3 = Sheryan|last4 = Rivero|first4 = Carlos|volume = 5|pages = 257–266|doi-access = free|hdl = 1834/30782|hdl-access = free}}</ref> However, leatherback sea turtles (family [[Dermochelyidae]]) are able to maintain a body temperature {{Convert|8|C-change}} warmer than the ambient water by thermoregulation through the trait of [[gigantothermy]].<ref name=":30" /><ref>{{Cite journal|last1=Paladino|first1=Frank V.|last2=O'Connor|first2=Michael P.|last3=Spotila|first3=James R.|date=1990-04-26|title=Metabolism of leatherback turtles, gigantothermy, and thermoregulation of dinosaurs|url=https://www.nature.com/articles/344858a0|journal=Nature|language=en|volume=344|issue=6269|pages=858–860|doi=10.1038/344858a0|bibcode=1990Natur.344..858P|s2cid=4321764|issn=1476-4687|url-access=subscription}}</ref>

Green sea turtles in the relatively cooler Pacific are known to haul themselves out of the water on remote islands to bask in the sun.<ref name=":2">{{Cite journal|url = http://www.nmfs.noaa.gov/pr/pdfs/species/turtlesymposium1997.pdf#page=82|title = Basking in Galapagos Green Turtles|last = Green|first = Derek|date = March 1997|journal = Proceedings of the 17th Annual Sea Turtle Symposium}}</ref> This behavior has only been observed in a few locations, including the [[Galapagos]], Hawaii, [[Europa Island]], and parts of Australia.<ref name=":2" /> [[Image:Chelonia mydas got to the surface to breath.jpg|thumb|A green sea turtle breaks the surface to breathe.|left]]

=== Diving physiology ===
{{see also|Physiology of underwater diving#Aquatic reptiles}}
Sea turtles are air-breathing reptiles that have lungs, so they regularly surface to breathe. Sea turtles spend a majority of their time underwater, so they must be able to hold their breath for long periods.<ref name=":8" /> Dive duration largely depends on activity. A foraging sea turtle may typically spend 5–40 minutes underwater<ref name=":8">{{Cite journal|title = Voluntary diving metabolism and ventilation in the loggerhead sea turtle|journal = Journal of Experimental Marine Biology and Ecology|date = 1991-05-16|pages = 287–296|volume = 147|issue = 2|doi = 10.1016/0022-0981(91)90187-2|first1 = Molly E.|last1 = Lutcavage|first2 = Peter L.|last2 = Lutz|doi-access = free| bibcode=1991JEMBE.147..287L }}</ref> while a sleeping sea turtle can remain underwater for 4–7 hours.<ref>{{cite web|title = Information About Sea Turtles: Frequently Asked Questions |url = http://www.conserveturtles.org/seaturtleinformation.php?page=seaturtle-faq#14 |publisher = Sea Turtle Conservancy|access-date = 2015-10-15}}</ref><ref name=":9">{{Cite journal|title = First records of dive durations for a hibernating sea turtle|journal = Biology Letters|date = 2005-03-22|issn = 1744-9561|pmc = 1629053|pmid = 17148134|pages = 82–86|volume = 1|issue = 1|doi = 10.1098/rsbl.2004.0250|first1 = Sandra|last1 = Hochscheid|first2 = Flegra|last2 = Bentivegna|first3 = Graeme C.|last3 = Hays}}</ref> Remarkably, sea turtle respiration remains [[Cellular respiration|aerobic]] for the vast majority of voluntary dive time.<ref name=":8" /><ref name=":9" /> When a sea turtle is forcibly submerged (e.g. entangled in a trawl net) its diving endurance is substantially reduced, so it is more susceptible to drowning.<ref name=":8" />

When surfacing to breathe, a sea turtle can quickly refill its lungs with a single explosive exhalation and rapid inhalation. Their large lungs permit rapid exchange of oxygen and avoid trapping gases during deep dives.

[[Cold-stunning]] is a phenomenon that occurs when sea turtles enter cold ocean water ({{Convert|45|–|50|F|abbr=on|order=flip}}), which causes the turtles to float to the surface and therefore makes it impossible for them to swim.<ref>Spotila, J. R. (2004). ''Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation''. Baltimore: Johns Hopkins University Press. {{isbn|978-0801880070}}</ref>

===Fluorescence===

Gruber and Sparks (2015)<ref name=Gruber_2015>{{Cite journal| last1 = Gruber| first1 = David F.| last2 = Sparks| first2 = John S.| title = First observation of fluorescence in marine turtles| journal = American Museum Novitates| issue = 3845| pages = 1–8| doi = 10.1206/3845.1| issn = 0003-0082| date = 2015-12-01| hdl = 2246/6626| s2cid = 86196418| url = http://digitallibrary.amnh.org/bitstream/2246/6626/1/N3845.pdf}}</ref> have observed the first [[fluorescence]] in a marine [[tetrapod]] (four-limbed [[vertebrate]]s).<ref>{{cite web| last = Lewis| first = Danny| title = Scientists just found a sea turtle that glows| work = Smithsonian  | date = 2015    | access-date = 2017-03-19| url = http://www.smithsonianmag.com/smart-news/scientists-discover-glowing-sea-turtle-180956789/}}</ref> Sea turtles are the first [[biofluorescent]] [[reptile]] found in the wild.

According to Gruber and Sparks (2015), [[fluorescence]] is observed in an increasing number of marine creatures ([[cnidarian]]s, [[Ctenophora|ctenophores]], [[annelid]]s, [[arthropod]]s, and [[chordate]]s) and is now also considered to be widespread in [[Chondrichthyes|cartilaginous]] and [[Actinopterygii|ray-finned]] fishes.<ref name=Gruber_2015/>

The two [[Marine biology|marine biologists]] accidentally made the observation in the [[Solomon Islands]] on a hawksbill sea turtle, one of the rarest and most endangered sea turtle species in the ocean, during a night dive aimed to film the [[biofluorescence]] emitted by small [[shark]]s and [[coral reef]]s. The role of biofluorescence in marine organisms is often attributed to a strategy for attracting prey or perhaps a way to communicate. It could also serve as a way of defense or [[camouflage]] for the sea turtle hiding during night amongst other fluorescent organisms like corals. Fluorescent corals and sea creatures are best observed during night dives with a blue [[Light emitting diode|LED]] light and with a camera equipped with an orange [[optical filter]] to capture only the fluorescence light.<ref>{{cite web| last = Lee| first = Jane J.| title = Exclusive video: first "glowing" sea turtle found| work = National Geographic News| access-date = 2017-03-19| date = 2015-09-28| url = http://news.nationalgeographic.com/2015/09/150928-sea-turtles-hawksbill-glowing-biofluorescence-coral-reef-ocean-animals-science150928-sea-turtles-hawksbill-glowing-biofluorescence-coral-reef-ocean-animals-science/| archive-url = https://web.archive.org/web/20150930220119/http://news.nationalgeographic.com/2015/09/150928-sea-turtles-hawksbill-glowing-biofluorescence-coral-reef-ocean-animals-science150928-sea-turtles-hawksbill-glowing-biofluorescence-coral-reef-ocean-animals-science/| url-status = dead| archive-date = September 30, 2015}}</ref><ref>{{Cite news| last = Hanson| first = Hilary| title = Scientists discover 'glowing' sea turtle| work = Huffington Post| date = 2015-09-29| access-date = 2017-03-19| url = http://www.huffingtonpost.com/entry/sea-turtle-glowing-discovery_us_560ac2a0e4b0dd8503094fd4}}</ref>

=== Sensory modalities ===

==== Navigation ====

Below the surface, the sensory cues available for navigation change dramatically.<ref name=":16">{{Cite journal|last1=Lohmann|first1=K. J.|last2=Lohmann|first2=C. M. F.|last3=Endres|first3=C. S.|date=2008-06-01|title=The sensory ecology of ocean navigation|journal=Journal of Experimental Biology |volume=211|issue=11 |pages=1719–1728|doi=10.1242/jeb.015792 |pmid=18490387|issn=0022-0949|doi-access=free|bibcode=2008JExpB.211.1719L }}</ref> Light availability decreases quickly with depth, and is refracted by the movement of water when present, celestial cues are often obscured, and ocean currents cause continuous drift.<ref name=":16" /> Most sea turtle species [[Sea turtle migration|migrate]] over significant distances to nesting or foraging grounds, some even crossing entire ocean basins.<ref name=":17">{{cite journal|last1=Lohmann|first1=Kenneth J. |last2=Putman|first2=Nathan F. |last3=Lohmann|first3=Catherine M. F.|date=2012|title=The magnetic map of hatchling loggerhead sea turtles|url=https://linkinghub.elsevier.com/retrieve/pii/S0959438811001954|journal=Current Opinion in Neurobiology |volume=22|issue=2|pages=336–342 |doi=10.1016/j.conb.2011.11.005 |pmid=22137566|s2cid=1128978|url-access=subscription}}</ref> Passive drifting within major current systems, such as those in the [[North Atlantic Gyre]], can result in ejection well outside of the temperature tolerance range of a given species, causing heat stress, hypothermia, or death.<ref name=":17" /> In order to reliably navigate within strong [[Ocean gyre|gyre]] currents in the open ocean, migrating sea turtles possess both a bicoordinate magnetic map and magnetic compass sense, using a form of navigation termed [[Magnetoreception]].<ref name=":17" /><ref name=":16" /><ref name=":18">{{cite journal |last1=Lohmann |first1=Kenneth J. |last2=Lohman |first2=Catherine M. F. |date=2019-02-06|title=There and back again: natal homing by magnetic navigation in sea turtles and salmon |journal=The Journal of Experimental Biology |volume=222|issue=Supplement 1 |pages=jeb184077 |doi=10.1242/jeb.184077 |pmid=30728225 |issn=0022-0949|doi-access=free|bibcode=2019JExpB.222B4077L }}</ref> Specific migratory routes have been shown to vary between individuals, making the possession of both a magnetic map and compass sense advantageous for sea turtles.<ref name=":17"/>

[[File:Hatchling green sea turtle.jpg|alt=Hatchling green sea turtle in the sand photographed by USFWS Southeast|thumb|Hatchling green sea turtle in the sand photographed by USFWS Southeast]]

A bicoordinate magnetic map gives sea turtles the ability to determine their position relative to a goal with both latitudinal and longitudinal information, and requires the detection and interpretation of more than one magnetic parameter going in opposite directions to generate, such as [[Magnetic field intensity]] and [[Inclination angle]].<ref name=":18" /><ref name=":20">{{Cite journal|last1=Fuxjager|first1=M. J.|last2=Eastwood|first2=B. S.|last3=Lohmann|first3=K. J.|date=2011-08-01|title=Orientation of hatchling loggerhead sea turtles to regional magnetic fields along a transoceanic migratory pathway |journal=Journal of Experimental Biology |volume=214|issue=15|pages=2504–2508 |doi=10.1242/jeb.055921|pmid=21753042 |issn=0022-0949 |doi-access=free|bibcode=2011JExpB.214.2504F }}</ref> A magnetic compass sense allows sea turtles to determine and maintain a specific magnetic heading or orientation.<ref name=":20" /> These magnetic senses are thought to be inherited, as hatchling sea turtles swim in directions that would keep them on course when exposed to the magnetic field signatures of various locations along their species' migratory routes.<ref name=":20" /><ref>{{Cite journal |last=Lohmann|first=K. J. |date=2001-10-12 |title=Regional Magnetic Fields as Navigational Markers for Sea Turtles |url=https://www.science.org/doi/10.1126/science.1064557 |journal=Science |volume=294 |issue=5541 |pages=364–366 |doi=10.1126/science.1064557 |pmid=11598298 |bibcode=2001Sci...294..364L |s2cid=44529493|url-access=subscription }}</ref>

[[Natal homing]] behavior is well described in sea turtles, and genetic testing of turtle populations at different nesting sites has shown that magnetic field is a more reliable indicator of genetic similarity than physical distance between sites.<ref name=":21">{{Cite journal|last1=Brothers|first1=J. Roger |last2=Lohmann|first2=Kenneth J.|date=2018|title=Evidence that Magnetic Navigation and Geomagnetic Imprinting Shape Spatial Genetic Variation in Sea Turtles |journal=Current Biology |volume=28|issue=8 |pages=1325–1329.e2 |doi=10.1016/j.cub.2018.03.022 |pmid=29657117|doi-access=free|bibcode=2018CBio...28E1325B }}</ref> Additionally, nesting sites have been recorded to "drift" along with isoline shifts in the magnetic field.<ref name=":22">{{Cite journal|last1=Brothers|first1=J. Roger|last2=Lohmann |first2=Kenneth J.|date=2015|title=Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles|journal=Current Biology |volume=25|issue=3 |pages=392–396 |doi=10.1016/j.cub.2014.12.035 |pmid=25601546|doi-access=free|bibcode=2015CBio...25..392B }}</ref> Magnetoreception is thought to be the primary navigation tool used by nesting sea turtles in returning to natal beaches.<ref name=":21" /><ref name=":22" /> There are three major theories explaining natal site learning: inherited magnetic information, socially facilitated migration, and geomagnetic [[Limbic imprint|imprinting]].<ref name=":18" /> Some support has been found for geomagnetic imprinting, including successful experiments transplanting populations of sea turtles by relocating them prior to hatching, but the exact mechanism is still not known.<ref name=":18" />