Have you ever wondered how turtles make it through the winter in iced-over ponds?
Turtles are ectotherms — that is, their body temperature reflects that of their environment. And the colder a turtle gets, the more its metabolism slows and the less oxygen it requires.
From here, nature has devised several ways for these air breathers to meet their needs. As long as some turtles can move pond water across vascular tissues, they can absorb the oxygen they need. It just so happens that one of the most blood-rich tissues is the rectum. So, in essence, these turtles breathe through their backsides.
Other turtles switch to anaerobic metabolism, which doesn’t use oxygen. In order to offset the acid buildup from this process, they use calcium from their shells as a sort of antacid.
Nature always finds an answer, and in such ingenious ways!