Marine Mammal Energetics

MARE 390Dr. Turner

Energetics

Employ a variety of methods to evaluate costs & benefits of specific life processes

Involves costs of acquiring resourcesevolution of adaptations to aquatic

existence - seawaterHow resources are allocated

cost benefit interactionsenergy-flow models

Energetics

Allocate energy across three uses: - burned in metabolism - allocated to growth - used in reproduction

Metabolic Fuels

Substrates used in metabolism fat, protein, carbohydrate, combination

2X energy metabolized from lipid than amount from protein or carbohydrate

Lipids > proportion of metabolic fuel

Greater proportion of lipids in diet

Metabolic Rate

Cellular mechanics similar to other verts

Typically other mechanisms when diving

Standardized units

Biological state of an organisms can affect metabolic rate

Basal Metabolic Rate (BMR)

Measure of the metabolic rate of mature (sex & phys), postabsorptive individuals at rest in a thermoneutral environment

BMR – used for comparison across groups

Ambient Temperature

Met

abo

lic

Rat

eLower lethal temp.

Lower critical temp.

Upper lethal temp.

Upper critical temp.

Thermo neutral zone (TNZ)

BMR

High and constant body tempcan be maintained at rest over a fluctuationof temperatures of 5-10 C with littleExtra metabolic work—this is the TNZ.

Most birds/mammals spend time in environments that fall within the TNZ

BMR & Body MassKleiber Curve – BMR to body mass to the 0.75 power (BMR = aM0.75)

Do marine mammals have higher metabolic rates??? – continues debate

Live in cold, highly conductive media

Heat capacity of water 25X air

Several adaptations to reduce heat loss:large body size – reduced SVRincreased insulationconserving counter-current systems

Provide broad thermoneutral zones

Thermoregulation

Body Mass – SAV Ratios

Marine mammals span a body-mass range 4X from sea otters (5kg) to blue whales (10x104)

Surface area of a body ↑ proportionally to the square of its lengthVolume (≈mass) ↑ proportional to its cube

Marine mammals capable of producing considerable heat with relatively little loss

Body Mass – SAV Ratios

SA/V Ratio ↑ ↓

Body Mass – SAV Ratios

Reduce heat loss by streamlining body form – reducing surface area

Surface area of pinnipeds, cetaceans, & sea otters are 23% < terrestrial mammals of similar body mass

Body Mass – SAV Ratios

Insulation

Use dense fur or blubber

Fur: depends upon capacity to trap air

Blubber functions: thermoregulation, energy storage, buoyancy control, streamlining

Non-shivering thermogenesis – brown fatlarge amounts in pups

Fur

Fur – extreme sea otter (150,000 hairs/cm2)

In air: impedes thermoregulation

In water: works well in shallow water environment

Deep divers – air squeezed out (pressure)

Blubber

Insulative value a function of thickness, lipid content, & peripheral blood flow

Cetaceans – mostly lipid content

Very efficient in cetaceans & pinnipedsless so in sirenians

manatees thinner than dugongs

Blubber

Sirenians – 2 blubber layers

Functionally cuts insulatory capability in half

Cetacean Manatee

Skin

Blubber

Muscle

SkinBlubber

Muscle

BlubberMuscle

Blubber

↓ Thermal Conductivity = ↑ Insulation

Peripheral Blood Circulation

Conserve heat in water (cold) – inhibits heat dissipation on land (warm)

Counter current heat exchangers – conserve heat by maintaining a heat differential between oppositely directed flows of blood

Counter Current Heat Exchangers

39°C 37°C 35°C 33°C 31°C 29°C27°C

38°C 36°C 34°C 32°C 30°C 28°C

Heat is conserved before it is lost at the extremity

Veins

Artery

Parallel intermingling vessels (in contact)

= vascular bundles (rete)

Counter Current Heat Exchangers

Pinnipeds & cetaceans - Flippers & fins (flukes)Use hindflippers & forsal fin to cool gonads

Sirenians – vascular bundles throughout body – expel heat in warm waters

Right & Gray whales – in mouths; when feeding in cold waters

Counter Current Heat Exchangers

Counter Current Heat Exchangers

Energetics of Locomotion

Up to 80% of daily activity budget

Frictional resistance of water has large effect – 800x more dense than air, 30x more viscous

Must overcome hydrodynamic drag

What a Drag

Frictional & Pressure Drag – associated with physical prcesses of water surrounding the body surface

Induced Drag – associated with water flow around the flippers, fins, & flukes

Wave Drag – moving at or near the surface

Body Streamlining

Drag reduced by streamlining body surface

Cost of Transport

Fitness ratio – measure of streamlining

Transport Adaptations

Wave Riding – large energetic savings - bow or stern of ships & whales

Surfacing only to breathe

Porpoising – removes animal from high drag environment at surface while breathing; mammals < 10m Crossover – velocity at which porpoising becomes more efficient (5m/s)

Osmoregulation

Hyposmotic – body fluids have a lower ionic content than surrounding water

losing water to hyperosmotic seawater

Larger kidneys than terrestrial mammals

Multi-lobed kidneys – reniculihuman & horses – single lobecetaceans – 450 to 3,000 reniculi

Osmoregulation

Osmoregulation

Cetaceans can concentrate urine to a greater extent than any other mammals

Allow them a net-gain to drinking seawater

In cetaceans: 1L seawater = 0.5L water gain

In humans: 1L seawater = 0.5L water loss

Strategic Energetics Approach

Model of how marine mammals respond to change