Conservation and Ecology of Marine Reptiles

MARE 494Dr. Turner

Summer 2007

Diving PhysiologyAmong longest and deepest diving vertebrates

Spend 3-6% time at surface

Central features of dive ability:efficient O2 transporttolerance for hypoxiamaximum used of limited O2 stores

Diving PhysiologyPhysiological traits of breath-hold mode are common reptilian traits

Present in land-dwelling ancestors

However, several distinct modifications to marine existence

parallels with marine mammals

Dive Records

Lung Structure & FunctionFew breaths (2-3s) at surface to empty & refill lungs

# breaths (time at surface) to increase with duration of submergence time

Tidal lung volumes greater than terrestrial or aquatic reptiles

marine mammals have greater tidal volumes than terrestrial

Lung Structure & FunctionSimilar structure to marine mammal lungs

Large-diameter airways are well enforced cartilaginous bronchioles smooth muscle with elastic fiber matrix

Lack a diaphragmPelvic, gular, & pectoral muscles

ventilate lungs

Lung Structure & Function

Phocid Otariid Odobenid

Under Pressure

Tolerate ↑ in water pressure

1 atmosphere (atm) for each 10mLeatherback > 1000m (100atm)

Squeezes air-filled spaces

Absorbing gases at high pressure can be toxic – damage from bubbles

Effect upon central nervous system

In Fact It’s a Gas

Sea turtles have the highest rates of O2 consumption and greatest aerobic scopes of any reptile

Can attain resting O2 consumption rates similar to rates of mammals

Greater area for gas exchange (diffusion) than most reptiles; lower resistance

It’s a Gas Gas Gas

High pulmonary diffusion capacity – advantage during prolonged submergence when sea turtles deplete lung, arterial, & venous O2 stores

Low-resistance lung – support high metabolic rates (maximum exercise) by maintaining high saturation levels in arterial blood

It’s a Gas Gas Gas

High pulmonary diffusion capacity – advantage during prolonged submergence when sea turtles deplete lung, arterial, & venous O2 stores

Low-resistance lung – support high metabolic rates (maximum exercise) by maintaining high saturation levels in arterial blood

Hope Floats

Regulate volume of air in lungs during shallow dives for buoyancy control

fine-scale – shifting among compartments

Also thought to quickly distribute blood warmed via heliothermy

Oxygen Transport

Dive duration a function of total O2 store and metabolic rate during the dive

metabolic rate a function of:SizeActivityTemperatureHormonal statusDietary status

O2 consumption – VO2

STÖR

Diving birds & mammals typically store O2 in blood & tissues

Amphibians & reptiles use lings as major O2 stores

Sea turtles – may center around shallow versus deep diving

SHØP

Shallow divers (Cheloniids)– depend upon lung as the major O2 store

Deep divers – (Dermochelyids) rely upon blood and tissue stores for O2

Hematocrit, hemoglobin, myoglobin concentrations among highest in reptiles similar to levels in marine mammals

Total Body Oxygen Stores

Largest O2 stores in diving mammals Hemoglobin – O2 binding molecule of

red blood cells; can deliver O2 where needed

Myoglobin – O2 binding molecule of muscle cells; delivers O2 directly to muscles

Hematocrit – packed red blood cell volume; hemoglobin volume – higher in mammals with increased diving capacity

Total Body Oxygen StoresResp – Cardio – Cellular = All EqualFewer mitochondria

Cellular dominantMore mitochondria

Total Body Oxygen Stores

Respiratory properties of blood depends upon whether O2 is primarily stores in tissues or in the lung

High hematocrit in leatherbacks – similar to marine mammals

Total Body Oxygen Stores

Total Body Oxygen Stores

Dive Response

During dive, available O2 ↓ (hypoxia) and CO2 ↑ (hypercapnia)

Together create asphyxia

Counteract with several adaptations:Anaerobic diving – no O2; lactic acid & H+ ions accumulateBradycardia – decline in heart rateIschemia – preferential distribution of blood to O2 sensitive organs;

temperature & metabolic rate

Diving Adaptations

Cease breathing during diving events apneic conditions – conflicting conditions1. O2 stores ↓ with ↑ activity (O2 demand)2. CO2 & lactate ↑ in blood & muscle

During hypoxic events, muscle activity is maintained anaerobically

results in ↑ accumulation of lactate

Low-Impact Aerobics

In the past 10-20 yrs – research emphasis on anaerobic dive physiology

Recent on aerobic dive limits and how animals stay within these limits

Know that aerobic diving is the only way to facilitate multiple sequential dives over a short period of time

Aerobic Dive Limit

Longest dive that does not lead to an increase in blood lactate concentration

If dive within ADL, can dive again immediately without recovery period

If dive exceeds ADL and accumulate lactate; surface recovery period is

required to “burn-off” (remove) lactic acid from the body

Aerobic Dive Limit

Leatherback

Total Body Oxygen Stores

Anoxia

Vertebrate brain has an absolute dependence upon O2 and dies within a few minutes without it Ultimate determinant of dive endurance in marine mammals

Some FW & sea turtles can survive several hours of anoxia

Anoxia

Unique mechanisms to protect brain

Anoxic turtle brain can maintain ATP levels & ionic homeostasis by severely reducing metabolic demands to a level met by anaerobic glycolysis

In FW turtles – used to survive hibernation

“You have an absolutely unique genetic condition known as ‘Homer Simpson syndrome’. Why, I could wallop you all day with this surgical two-by-four without ever knocking you down. But... I have other appointments.” – Dr. Julius Hibbert

Hibernation

In FW turtles – used to survive hibernation in frozen over hypoxic ponds

In Sea Turtles???

Torpid hibernating sea turtles – may survive 1-3 months (presumably without eating or breathing)

Know that cold can effect some animals“cold stunned” coma

Diving Pau

Huge gaps in knowledge (sounds familiar?)

Possibly with newly developed sensors…

In order to reduce deaths in fishing gear…

Maybe Sargassum has an effect???