Beginner 7 minutes
Marine reptiles: turtles, snakes, and a few unique cases
A group small in number of species, but central to any diver's experience
A green sea turtle can spend decades roaming an entire ocean and, when it's time to lay eggs, return to nest on the very same beach where she was born. No maps, no coastline in sight, across thousands of kilometers of open water.
In this article you'll learn about the groups of reptiles that colonized the sea (sea turtles, sea snakes, and a few singular cases) the adaptations they share, and the guidelines for observing them without interfering.
Sea turtles are among the animals divers most want to see, and also among the most frequently disturbed without any bad intent. Knowing how they work explains exactly why certain behaviors harm them.
What all marine reptiles have in common
Marine reptiles are a much smaller group than fish or invertebrates, but they share a set of very distinctive solutions. All of them breathe air with lungs and must come up to the surface; all of them have skin covered in keratinized scales; and all of them are ectotherms, meaning they depend on their environment to regulate their body temperature, unlike marine mammals.
That thermal dependence explains why most of them live in tropical and subtropical waters: they can't generate enough internal heat to survive in cold seas.
They also all share a problem land animals don't have: excess salt. By living in and ingesting seawater, they need to eliminate salt constantly, and they solve it with specialized salt glands. In sea turtles, those glands sit next to the eyes, and their secretion is the reason a female nesting on the beach appears to be crying. It's not emotion, it's physiology.
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