Sea Turtles

[[Lecture16_SeaTurtles_NOTES_2perPg.pdf|Link to slides]]

Testudines (Turtles)

  • Protective shell: Turtles have specialized shells that serve as a protective structure, with their vertebrae, ribs, and pectoral/pelvic girdles fused into the shell for enhanced defense.

  • Skull Structure: Turtles lack temporal fenestrae in their skulls, and they do not possess teeth, which is distinct from many other reptiles.

  • Evolutionary Divergence: Turtles diverged from archosaurs more than 250 million years ago, making them one of the oldest reptile lineages still in existence.

Morphology

  • Shell Structure: The shell is the most notable feature of turtles, with the top half referred to as the carapace and the bottom half as the plastron.

  • Scutes and Scales: The shell is covered with scutes, which are hard protective plates, while scales are produced from the external layers of the epidermis.

Turtle Diversity

7 Extant Species of Sea Turtle:

  1. Leatherbacks:

    • Size: The largest sea turtle, with a straight carapace length (SCL) of up to 8 feet.

    • Composition: Features a cartilaginous matrix instead of a bony shell.

    • Behavior: Known for being the deepest divers among sea turtles, capable of reaching depths greater than 1000 meters.

    • Diet: Primarily feeds on soft-bodied invertebrates such as jellyfish.

    • Distribution: Found in oceans worldwide (circumglobal distribution).

  2. Flatbacks:

    • Size: Average SCL of around 3 feet.

    • Features: Characterized by a flattened shape and smooth shell.

    • Diet: Primarily feeds on crabs.

    • Habitat: Restricted to the Indo-Pacific region, particularly around Australia; least studied due to their limited range and coexistence with saltwater crocodiles.

  3. Green Sea Turtles:

    • Size: Can reach up to about 4 feet in SCL.

    • Coloration: Notable for wide color variation of their shells.

    • Historical Use: Once heavily harvested as a food source.

    • Diet: Juveniles primarily consume invertebrates, while adults are known to eat seagrass and algae, aiding in the health of seagrass beds.

    • Habitat: Commonly found in tropical to subtropical regions; juveniles can often be seen in North Carolina waters.

  4. Hawksbill:

    • Size: Typically grows up to 3 feet in SCL.

    • Characteristics: Features a sharply pointed beak, advantageous for feeding.

    • Conservation Violation: Historically harvested for their beautiful shells, which were used in jewelry and ornaments.

    • Diet: Forages primarily on reef sponges, playing a crucial role as a consumer in coral reef ecosystems.

    • Habitat: Found mainly in tropical to subtropical waters.

  5. Loggerhead:

    • Size: Can reach about 4 feet in SCL.

    • Anatomy: Named for its large head and powerful jaws, adapted for crushing prey.

    • Diet: Primarily feeds on benthic invertebrates like crabs.

    • Distribution: Commonly found in tropical to subtropical latitudes, and noted for being the most frequent sea turtle species nesting on North Carolina beaches.

  6. Olive Ridley:

    • Size: Approximately 2 feet in SCL.

    • Shell Shape: Heart-shaped shell with an olive coloration.

    • Diet: Feeds mainly on benthic invertebrates.

    • Reproductive Behavior: Known for unique 'arribada' nesting behavior, where females gather to lay eggs en masse.

    • Population Status: Considered one of the most abundant sea turtle species.

  7. Kemp’s Ridley:

    • Size: Up to about 2 feet in SCL.

    • Shell Characteristics: The shell length and width are approximately equal, facilitating streamlined movement through the water.

    • Feeding: Feeds on benthic invertebrates, similar to the Olive Ridley.

    • Habitat: Restricted primarily to the Gulf of Mexico and the East Coast; noteworthy for their mass nesting behavior.

    • Conservation Status: The most endangered sea turtle species, with significant conservation efforts in place to protect their nesting sites and habitats.

Cardiorespiratory Adaptations

  • Historical Context: In the 1940s, Per Scholander conducted studies on seals that revealed significant physiological changes during force dives under lab conditions.

  • Vertebrate Dive Response: Key components include:

    • Apnea: The act of holding breath to maximize dive times.

    • Peripheral Vasoconstriction: Constriction of blood vessels directs blood to essential organs relying on oxygen, effectively managing oxygen utilization during dives.

    • Bradycardia: A reduction in heart rate, assisting in maintaining blood pressure despite reduced heart function.

Other Key Points:

  • Aerobic Dive Limit: Represents the maximum dive duration achievable without increasing lactic acid levels, indicating the onset of anaerobic metabolism, which is crucial for conservation of oxygen stores.

  • Oxygen Transport Proteins:

    • Hemoglobin: An oxygen-binding protein in blood, facilitating oxygen transport.

    • Myoglobin: An oxygen-binding protein in muscle, crucial for storing oxygen during extended dives.

Sensory Adaptations

  • Magnetoreception: Refers to the ability of turtles to perceive magnetic fields, which aids in navigational abilities.

  • Nest Development: Magnetic imprints influence their development while in the nest, impacting long-term migratory behavior.

Thermal Adaptations

  • Seasonal Migration: Sea turtles migrate seasonally to evade colder waters, moving toward lower latitudes or deeper offshore waters in winter.

  • Cold Stunning: Condition characterized by rapid drops in water temperature (<10°C), causing lethargy in turtles and loss of their ability to dive, potentially leading to exposure to cold air.

  • Leatherback Cold Adaptations: Unique adaptations include:

    • Countercurrent Heat Exchangers: Located at the base of their flippers to retain heat.

    • Fat Layers: Thick, well-vascularized fat layers that enhance heat retention.

    • Body Size: Their larger body size aids in maintaining higher body temperatures during dives.