The Missing 45-60 Days: Embryonic Development of Sea Turtles

Blog Post By: Ashlyn, Sea Turtle Intern
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This season, countless campers, vacationers, volunteers, and friends of the turtle patrol have gotten to witness the miracles of both mature loggerhead sea turtles emerging onto land to nest and hatchlings emerging from the sand to make their first crawl back to the ocean. It is the process we don’t necessarily get a chance to witness, however, that is the most miraculous of all in my sight. In those 45-60 days of incubation, in between the time a clutch of eggs is laid and the baby turtles hatch, that embryonic development occurs. That clutch of eggs goes from shell and yolk to a fully formed turtle in less than two months. That in itself is something to marvel over! But what exactly is occurring in that short period of time?

The embryonic development of sea turtles can be broken into 31 unique and complex stages! These 31 stages, however, can be categorized into five overall developmental processes.

1. Fertilization—Gastrulation—Early Neurulation
After fertilization has occurred, the zygote forms a blastocyst, a multilayered cluster of cells. Reorganization of this cell cluster occurs quickly, as cells move along a central line termed the primitive streak, folding to form three primary dermal layers: the endoderm, ectoderm, and mesoderm. Neurulation initiates in this early stage of development, as cells fold to prepare for the head and spinal cord development.

2. Neurulation—Somitogenesis
​The neural tube, the precursor of the spinal cord region develops at this stage. The head, brain, heart, and blood vessels begin to develop. Specialized precursor cells called somites begin to form clusters. These somites will eventually differentiate into important structures within the body such as muscles, skin, cartilage, and vertebrae.

3. Somitogenesis—Organogenesis
The embryonic cell layers become more complex during this stage, giving rise to tissues and organs.

4. Early Growth
All the major bodily organs and systems continue to grow and develop. The limbs, ribs, carapace develop.

5. Late growth—Hatching
Growth of the organs and systems comes to completion as the developed sea turtle prepares to hatch from the chamber and emerge onto the beach. In this final embryonic development stage, pigmentation completes and the remaining nutritional yolk decreases.
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I can discover and mark a sea turtle nest in May and watch the hatchlings emerge in July. But digging deeper, understanding the mechanism for developmental transformation, allows me to gain an even greater appreciation for the circle of life that I have been a witness to all summer long. Perhaps science and miracles go hand in hand.