What temperature do sea turtles live in?

Sea turtles are poikilothermic, meaning that they can not sufficiently internally maintain their internal body temperature and must absorb heat from the surrounding environment to maintain optimal body temperature. For this reason, they are particularly sensitive to ambient temperature and seek to occupy warmer waters, typically in the tropical and temperate zones and ideally over 20ºC. Exposed to temperatures below 10ºC, sea turtles may develop a condition called cold-stunned, a kind of hypothermia, if not treated.

Adult female green turtle on a colourful reef, Lhaviyni Atoll, Maldives. Image. — Holiday, female green turtle, relaxing on a reef in tropical waters.

References:

Hochscheid, S., Bentivegna, F., & Speakman, J. R. (2002). Regional blood flow in sea turtles: implications for heat exchange in an aquatic ectotherm. Physiological and Biochemical Zoology, 75(1), 66-76.
Schofield, G., Bishop, C. M., Katselidis, K. A., Dimopoulos, P., Pantis, J. D., & Hays, G. C. (2009). Microhabitat selection by sea turtles in a dynamic thermal marine environment. Journal of Animal Ecology, 78(1), 14-21.