Overview
This lecture covers the biology, anatomy, ecology, life cycle, evolution, and conservation status of sea turtles, including threats and human interactions.
Taxonomy and Species
- Sea turtles belong to superfamily Chelonioidea within order Testudines and suborder Cryptodira.
- There are seven species: flatback, green, hawksbill, leatherback, loggerhead, Kemp's ridley, and olive ridley.
- Six species are found in U.S. waters (all but flatback) and are listed as endangered or threatened.
- The flatback turtle is native to Australia, Papua New Guinea, and Indonesia.
Anatomy and Physiology
- Sea turtles can have hard shells (cheloniid) or leathery shells (dermochelyid); only the leatherback is dermochelyid.
- Males and females are similar in size; adults can be sexed by tail length.
- Sea turtles have a fusiform (streamlined) body and cannot retract limbs into their shells.
- Leatherback turtles are the largest species, reaching up to 1.8 meters and 640 kg.
- All sea turtles rely on lachrymal glands to excrete excess salt.
Life Cycle and Behavior
- Sea turtles live in oceans except polar regions, often over continental shelves and in sargassum mats when young.
- Females lay eggs on sandy beaches, often returning to their natal site.
- Eggs exhibit temperature-dependent sex determination: warmer sand yields females, cooler yields males.
- Hatchlings emerge mostly at night; larger hatchlings have a higher chance of survival.
Evolution and Phylogeny
- Fossil marine turtles date to the Late Jurassic; modern sea turtles form a single evolutionary radiation.
- Closest living relatives are snapping turtles, musk turtles, and hickatee.
Adaptations
- Limbs have evolved for both swimming and manipulating food.
- Leatherbacks maintain body temperatures above water via gigantothermy.
- Sea turtles have magnetic navigation and can travel thousands of kilometers to nesting sites.
Diet
- Loggerhead, Kemp's ridley, olive ridley, and hawksbill are lifelong omnivores.
- Green turtles shift from omnivory as juveniles to herbivory as adults.
- Leatherbacks mainly eat jellyfish; hawksbills primarily consume sponges.
Ecology and Ecosystem Roles
- Sea turtles help maintain healthy seagrass beds and dune vegetation through nesting.
- They participate in mutualisms, e.g., with yellow tang fish removing algae from shells.
- Barnacles often live on sea turtle shells, aiding barnacle dispersal.
Conservation Status and Threats
- Three species are endangered or critically endangered; three are vulnerable; flatback is data deficient.
- Major threats include bycatch in fishing gear, habitat loss, poaching, pollution, plastic ingestion, and climate change.
- Conservation efforts include protected nesting sites, legal protections, and rehabilitation programs.
Human Interaction
- Sea turtles have been hunted for meat, eggs, shells, and leather.
- Ecotourism has replaced hunting in some regions, supporting local conservation.
- Volunteers and organizations protect nests and assist hatchlings in reaching the sea.
Key Terms & Definitions
- Chelonioidea — Superfamily comprising all sea turtles.
- Dermochelyidae — Family including only the leatherback sea turtle.
- Cheloniidae — Family containing the other six sea turtle species.
- Temperature-dependent sex determination — Sex of hatchlings is determined by incubation temperature.
- Philopatry — Tendency to return to birthplace to reproduce.
- Lachrymal gland — Gland used by sea turtles to excrete salt.
- Bycatch — Unintentional capture of non-target species in fishing gear.
- Gigantothermy — Maintenance of elevated body temperature due to large size.
Action Items / Next Steps
- Review conservation status and threats for each sea turtle species.
- Study the life cycle diagram and key adaptations of sea turtles.