sea turtles

Purpose of turtle shell

Modified ribcage

Oviparous

Reproductive strategy of laying eggs

K-strategists

Produce few offspring but invest significant parental care in their growth and survival.

Turtle life expectancy

Often over 50, sometimes over 100 for large terrestrial species

Cosmopolitan distribution of turtles

terrestrial, freshwater, and marine habitats

Ectotherms

Activity and distribution are dependant on environmental termperature

TDS

temperature dependent sex determination

Secondary aquatic

Sea turtles breathe air

Sea turtle skin is covered with

Scales and scutes (keratinous layer of epidermis)

Sea turtle adaptations to marine environment

• Shell is reduced and has hydrodynamic shape

• Front and hind legs are flippers

• Can’t contract into shell

• Salt glands (turtle tears)

Living families of sea turtles

1. Dermochelyidae (leatherback)

2. Cheloniidae (6 species)

Life history patterns

• Neritic developmental pattern (Natator depressus)

• Oceanic developmental pattern (Dermochelys coracia & Lepidochelys olivacea)

• Oceanic-neritic developmental pattern (All other species)

Relaxed life history model

Status

evaluation of populations relative to some standard/goal

Harvest objectives

Population size/level that would support sustainable yield/catch

Conservation objectives

Ranging from preventing the extinction of species to returning populations to their “natural”/ carrying capacity level

Conservation status metrics

Population trends and probability of extinction

Threatened species classification

Critically engangered (CR), Endangered (EN) and Vulnerable (VU)

Conservation metric/criteria

Population reduction (A), Restricted distribution decline or fluctuation (B), Small population size and decline (C), very small or restricted (D), and quantitative analysis (E)

Shell breakdown

Dorsal shell (carapace), ventral shell (plastron), keratinous plates (scutes)

Evolution of shell on land

Turtles related to pareiasaurus, outside-in evolution of shell, teeth in upper jaw

Aquatic shell evolution

Turtles related to diapsids, inside-out evolution of shell, teeth in upper and lower jaw

First turtle and sea turtle

First turtles ≈ 220 MYA, first sea turtles ≈ 110 MYA

Fam. Dermochelyidae identification

Leatherback turtle (dermochelys coriacea) - leathery shell, no scutes and longitudinal dorsal ridges

Olive ridley identification

Lepidochelys olivacea

• 2 pairs of prefrontal scales

• 5 or more costal scutes, first costal scute touches nuchal scute

• 4 inframarginal scutes with pores

• 6 or more costal scutes

Kemp’s ridley identification

Lepidochelys Kempii

• 2 pairs of prefrontal sales

• 5 or more costal scutes, first costal scute touches nuchal scute

• 4 inframarginal scutes with pores

• 5 costal scutes, rounded carapace

Loggerhead identification

Caretta caretta

• 2 pairs of prefrontal scales

• 5 costal scutes, first costal scute touches nuchal scute

• 3 inframarginal scutes without pores

Hawksbill identification

Eretmochelys imbricata

• 2 pairs of prefrontal scales

• 4 costal overlapping scutes, first costal scute does not touch nuchal scute

• 4 inframarginal scutes without pores

Flatback identification

Natator depressus

• 1 pair of prefrontal scales

• 4 costal scutes, first costal scute does not touch nuchal scute

• 4 inframarginal scutes without pores

• Flattened carapace with upturned edges

Green turtle identification

Chalonia mydas

• 1 pair of prefrontal scales

• 4 costal scutes, first costal scute is not in contact with nuchal scute

• 4 inframarginal scutes without pores

• Rounded head, serrated lower jaw

CCL and CCW

CCL - cuved carapace length

CCW - curved carapace width

Heat exchange

• radiation: solar radiation

• conduction: heat transfer by direct physical contact

• convection: heat transfer by currents of moving fluid

Reptiles control their body temperature by

Thermoregulatory behavior, morphological characters, physiological processes

Physiology and thermoregulation

Cardiovascular control and heat production

Cardiovascular control

• changes in heart rate

• control of peripheral circulation

Heat production

• muscular production

• metabolic heat production

• counter-current heat exchange

Counter-current heat exchange in sea turtles

Loggerhead and green turtles: radial form
Leatherback turtle: matrix form

How do leatherback turtles maintain higher body temp than surrounding water?

• regional endothermy

• thermal inertia

• control of peripheral circulation

Morphology and thermoregulation

• morphological characters like crests (not sea turtles)

• Dark colors (melanism)

Thermoregulatory behavior

Because environmental heat loads vary with time and among habitats, reptiles attempt to buffer variation by selecting thermally suitable habitats, restriction of activity time, adopting specific positions and postures

Temperature Dependant Sex Determination

Thermal biology of nest for loggerheads

Nesting pivotal temp: 29.3 C

Incubation: 52.6 days

Nest depth: 50 cm

Reproduction migrations

Adult females move from foraging grounds to reproductive habitats (2-4)

Reproductive habitats constraints

• Conditions for adult activity

• Conditions for embryonic development

• Survival of hatchlings

Nesting process

1. Beach selection / ascending the beach

2. Excavating the body pit (5-10 min)

3. Digging the egg chamber (20 min)

4. Ovoposition (20-30 min)

5. Filling the egg chamber (10 min)

6. Filling the body pit (10 min)

7. Returning to the sea

Beach Selection

Must be accessible from the sea, high enough to prevent inundation, moist substrate and fine sand must prevent the egg chamber from collapsing, particle size must facilitate gas diffusion

Philopatry

Regional discrimination of reproductive regions

Site fidelity

Fine scale homing to beach

Reproductive biology stats

• remigration period: 2-4 years

• Nest depth 50-80 cm for constant temp

• 2-4 nests/reproductive season

• 10-14 day internesting interval

Embryonic development stats

• fertility: >80%

• Sex determination: TSD

• Pivotal temperature ≈ 29 C

• Incubation period: 50-80 days

• Hatching success >80%

Hatchling emergence

• Break out of shell (pipping)

• Quiescent period (around 1 day) for resorption of yolk

• Social facilitation (mutual stimulation)

• Synchronized upward digging through nest

• Inhibition of movements at high temperature

• En-masse emergences at night and early morning (1-7 days after pipping)

Orientation and navigating after emergence

• sea finding: visual cues (orientation towards brighter, lower oceanic horizon)

• nearshore waters (wave refraction zone): wave orientation (24-48 hour swimming frenzy to open ocean)

• open ocean: magnetic orientation

“Reproductive population” sea turtles in Mediterranean

Caretta caretta and chelonia mydas

“Rare visitor” sea turtles in the Mediterranean

Eretmochelys imbricata and lepidochelys kempii

“Vagrant” sea turtles in the Mediterranean

Dermochelys coriacea

Green sea turtle reproductive populations

Major green turtle rookeries: Turkey, Cyprus, and Syria

Mean nest number change 2000-2016: +47.1%

Regional IUCN status: Near threatened B2b(ii,iii)

Conservation dependent

Loggerhead sea turtle reproductive populations

most clutches laid in greece, turkey, libya, and cyprus

mean nest number change since 2000-2016: +26.4

regional iucn status: least concern

conservation dependent

Polyandry

clutch fertilized by several males - multiple paternity (microsatellite DNA analysis)

Polyandry fitness benefits

• secured fertilization

• selection of genetic material

• higher genetic variability of offsprings

Polyandry costs to females

• increased mortality risk

• increased predation risk

• increased energetic costs

Natal orign of adult females in mediterranean

90% greece, turkey, and cyprus - ionian/adriatic management unit

Haplotype frequency

CC-A1: endemic for atlantic

CC-A2, CC-A3: shared atlantic and mediterranean (found using mixed stock analysis)

Visitor, visiting taxon

A taxon that does not reproduce within a region but regularly occurs within its boundaries either now or during some period of the last century

Sea turtle thermal vulnerability potential positive effects

Foraging sites may expand with temperature rise

seagrasses may flourish with increased CO2

Sea turtle thermal vulnerability negative effects

High sea surface temp = reduction in ocean productivity

Ocean acidification disrupts coral reefs and seagrasses (lower diversity and abundance)

Increased storm intensity changes foraging conditions

Sea turtle thermal vulnerability species risk assessment

Coastal areas are better protected

equator and subtropics experience thermal novelty

herbivorous and diet specific species worse off