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The physiology of underwater diving is the physiological adaptations to diving of air-breathing vertebrates that have returned to the ocean from terrestrial lineages. They are a diverse group that include sea snakes, sea turtles, the marine iguana, saltwater crocodiles, penguins, pinnipeds, cetaceans, sea otters, manatees and dugongs.
Sea turtles spend a majority of their time underwater, so they must be able to hold their breath for long periods. [57] Dive duration largely depends on activity. A foraging sea turtle may typically spend 5–40 minutes underwater [57] while a sleeping sea turtle can remain underwater for 4–7 hours.
Elephant seals stay at sea for between 2 and 8 months and dive continuously, spending 90% of their time underwater and averaging 20 minutes per dive with less than 3 minutes at the surface between dives. Their maximum dive duration is about 2 hours and they routinely feed at depths between 300 and 600 m, though they can exceed depths of 1600 m.
Unlike in terrestrial turtles, the cornea (the curved surface that lets light into the eye) does not help to focus light on the retina, so focusing underwater is handled entirely by the lens, behind the cornea. The cone cells contain oil droplets placed to shift perception toward the red part of the spectrum, improving color discrimination.
Although only seven turtle species are truly marine, many more dwell in brackish waters. [1] [6] Sea snakes: the most abundant of the marine reptiles, there are over 60 different species of sea snakes. They inhabit the tropical and subtropical waters of the Indian and Pacific oceans, though very limited reports of sightings suggest they may be ...
Hundreds of dead, vulnerable sea turtles washed up on South Asian beaches last week near the city of Chennai, India. These turtles were identified as olive ridley turtles, an endangered species ...
Cold-stunned sea turtles may float to the surface and be further exposed to cold temperatures, which can cause them to drown. [1] A water temperature threshold of 8 [2] –10 °C [3] has been associated with mass turtle stunning events. After cold-stunning has taken place, there is only a very short period of time when sea turtles can be safely ...
Water clarity is a descriptive term for how deeply visible light penetrates through water. In addition to light penetration, the term water clarity is also often used to describe underwater visibility. Water clarity is one way that humans measure water quality, along with oxygen concentration and the presence or absence of pollutants and algal ...