Figure 31.5: The O2 Supply for Sea Turtle Eggs Depends on whether the Sand in which They Are Buried Is Dry or Wet The O2 partial pressure in a nest of sea turtle eggs depends on how fast the developing turtles use O2 and how fast O2 is resupplied by diffusion from the atmosphere. During the first 50 days of development in the nest studied here, the sand was dry and O2 diffused into the nest as fast as the developing turtles used O2—keeping the O2 partial pressure in the nest high. When the sand became soaked with water for 2 days, as the developing turtles used O2, the O2 they used was not replaced, and their metabolism reduced the O2 partial pressure to zero.