Marine Reptiles - Turtle Biology and Ecology Vocabulary Flashcards

Core Characteristics of Marine Reptiles

Taxonomic Groups: The primary groups of marine reptiles include: * Sea Turtles * Sea Snakes * Saltwater Alligators (Crocodilians) * Marine Iguanas
Physiological Traits: * Ectothermic (Poikilotherms): Animals whose internal body temperature varies according to the temperature of their environment. * Air Breathing: They rely on lungs for respiration rather than gills. * Integument: Possess scales and thick skin to withstand marine environments. * Salt Glands: Specialized organs used to excrete excess salt for osmoregulation.

Marine Iguanas (Amblyrhynchus cristatus)

Endemic Range: Exclusively found on the Galapagos Islands, located just off the Equator.
Dietary Habits: They are herbivorous, primarily consuming algae and seaweed. * While often thought to feed primarily underwater, recent research indicates significant feeding occurs intertidally among females and juveniles. * Hindgut Fermenters: They possess endosymbiotic bacteria to aid in the breakdown of algae. * Daily sustainment: $30\,g$ of algae per day is sufficient to sustain a $1\,kg$ animal.
Biological and Behavioral Traits: * Feeding: Only lizard known to feed at sea. * Diving: Large males can dive to depths of $10-12\,m$ and remain submerged for up to an hour. * Social Structure: Highly social, with densities reaching $8000$ individuals per kilometer of coastline. * Size Dimorphism: There are massive size differences between islands based on ecological factors (e.g., cold water upwelling nourishing algae): * Fernandina/Isabela: Males weigh $10+\,kg$ , females weigh less than $3\,kg$ . * Genovesa: Males weigh approximately $1\,kg$ , females weigh less than $1\,kg$ . * Reproduction: * Males are territorial, guarding breeding 'leks' and engaging in battles. * Coloration is influenced by diet. * Females fight over nesting sites. * Clutch size is $1-6$ eggs laid in the sand. * Females guard eggs for up to $2\,weeks$ . * Incubation is long, lasting approximately $95\,days$ .

Sea Snakes and Saltwater Crocodilians

Sea Snakes: * Belong to the family Elapidae. * Comprise $69$ species across two subfamilies. * Native to the warm coastal waters of the Indian and Western Pacific Oceans. * Characteristics: Highly venomous, excellent swimmers, feed primarily on small fish. * Predators: Predators include saltwater crocodiles, raptors (birds of prey), and sharks.
Saltwater Crocodiles (Crocodylus porosus): * Part of the Crocodylidae family (which contains $2$ genera and $13$ species). * Size: Largest of all reptiles, growing to lengths greater than $6\,m$ . * Behavior: Found in the tropical Western Pacific; capable of being found $1000\,km$ from land. * Nesting: They are mound-nest builders, using vegetation and soil. They display parental care towards their eggs. * Reproduction: Internal fertilization; oviparous.

Evolutionary History and Adaptations of Sea Turtles

Ancient Heritage: * Sea turtles share a common ancestor with other turtles from over $120$ million years ago. * Archelon ischyros: The world's largest extinct sea turtle from the Cretaceous Period ( $70$ million years ago). * Dermochelyidae lineage: Shared a common ancestor with other species $40$ million years ago (excluding the leatherback).
Aquatic Adaptations: * Streamlining: Shells became more hydrodynamic. * Modified Limbs: Limbs evolved into flippers; forelimbs generate lift through strokes, while hindlimbs are used for steering. * Speed: Capable of swim speeds up to $35\,mph$ . * Respiratory: Dense lung construction. Leatherback lungs are particularly spongy and deep red due to high surface area, dense parenchyma, high connective tissue levels, and extensive blood supply. * Limitation: Oviparity (laying eggs) prevents turtles from becoming entirely aquatic, as they must return to land.

Taxonomy of Modern Sea Turtles

Family Cheloniidae (Hard-shelled turtles): 1. Loggerhead (Caretta caretta): $5$ lateral scutes, $3$ inframarginal scutes without pores, more than $1$ pair of prefrontal scales. 2. Green Turtle (Chelonia mydas): Includes the Black turtle (Chelonia mydas agassizi). $4$ lateral scutes, $1$ pair of prefrontal scales. 3. Hawksbill (Eretmochelys imbricata): $4$ lateral scutes, imbricated (overlapping) scutes, $2$ pairs of prefrontal scales. 4. Kemp's Ridley (Lepidochelys kempii): $5$ lateral scutes, $4$ inframarginal scutes with pores. 5. Olive Ridley (Lepidochelys olivacea): $6$ or more lateral scutes, $4$ inframarginal scutes with pores. 6. Flatback (Natator depressus / formerly Chelonia depressus).
Family Dermochelyidae: 1. Leatherback (Dermochelys coriacea): Distinct from Cheloniidae; no scales on head, no scutes on shell (instead has ridges and leathery skin).

Life History and Migratory Cycles

The General Cycle: * Nesting Beach: Females lay eggs. * Hatchlings: Emerge after $50-80\,days$ and enter the ocean. * Pelagic Nursery Stage: Small turtles spend $5-20\,years$ in the open ocean. * Nearshore Foraging Areas: Immature and adult turtles move to shallow waters. * Breeding Migration: Adults migrate to breeding areas. Males return to foraging areas after breeding; females return to nesting beaches approximately every $2\,weeks$ during the season to lay multiple clutches.
Migration Case Study: Ascension Island: * Green turtles from rich feeding grounds off the coast of Brazil swim approximately $2300\,km$ against the current to reach Ascension Island (a tiny $10\,km$ target) in the middle of the Atlantic. * The trip takes $1-1.5\,months$ . * Hypothesis: This extreme migration relates to the fact that turtles have existed for hundreds of millions of years, potentially predating the current distance between the landmasses due to plate tectonics.

The Ecology of the Nesting Beach

Historical Context: Marine turtle research was negligible before the 1950s. Most early research focused on nesting beaches due to logistic accessibility, making "at-sea" knowledge anecdotal for a long time.
The Nest Environment: Includes the sand surface, the egg mass, and specific measurements for the depth to the topmost and bottom-most eggs.
Impact of Temperature: * Development: Thermal tolerance range for embryos is $25-27^\circ C$ to $33-35^\circ C$ . * Variability: Temperature decreases with sand depth. Uniform temperatures lead to a uniform rate of development. * External Factors: Tidal inundation decreases both temperature and oxygen levels in the sand column.
Temperature Sex Determination (TSD): * Pattern: Cool temperatures produce males; warm temperatures produce females (opposite to crocodilians). * Pivotal Temperature: Approximately $28-30^\circ C$ . At this temperature, the sex ratio is mixed. * Thermal Sensitive Period: The middle third of the incubation period. * Significance: This process is independent of metabolic heating.
Hatchling Emergence: * Utilizes social facilitation and group cooperation to dig out of the nest. * They respond to thermal gradients. * Orientation Mechanisms: 1. Visual cues (on the beach). 2. Wave orientation (in the wave refraction zone). 3. Magnetic orientation (in the open ocean).

Foraging Ecology and Diving Behavior

Leatherback Foraging in the Irish Sea: * Surveys (2003-2005) identified hotspots like Carmarthen Bay, Rosslare Harbor, and Tremadoc Bay. * Leatherbacks aggregate where their prey, jellyfish (Rhizostoma octopus and Chrysaora hysoscella), are abundant. * The peak season for sightings in the UK/Ireland is between July and September.
Deep Diving Dynamics: * Dives typically range by frequency, with many dives occurring in the $0-100\,m$ range ( $22,013$ recorded dives). * Exceptional Dives: Leatherbacks have been recorded diving deeper than $1200\,m$ . * Reasons for Deep Diving: 1. Predator evasion. 2. Thermoregulation. 3. Exploration for gelatinous prey (jellyfish). * Observations: Deep dives mainly occur around midday, usually when the turtle is in transit, at a steady rate. Research suggests they are searching for suitable prey that might surface during the night.