Marine mammals have evolved a range of characteristics that help them retain heat in cold water. State FOUR such characteristics. Briefly explain the significance of each of these four characteristics.

Question 1

Explain how lower body temperature helps them retain heat in colder water:

Answer 1

Lower body temperature:
• The body temperature of Cretaceans is slightly lower (35.5 degrees Celsius) than that of most mammals (36-38 degrees Celsius)
• This lowers the temperature differential between the animal and ambient temperature and therefore reduces the rate of heat loss

Question 2

Explain how a larger body size helps them retain heat in colder water:

Answer 2

• Even the smallest marine mammals are relatively large (e.g. one or two orders of magnitude larger than small terrestrial animals)
• Most have only one relatively large offspring per pregnancy
• Large body provides less surface area per unit volume over which to lose heat; it also allows for thicker insulation

Question 3

Explain how insulation (blubber) helps them retain heat in colder water environments:

Answer 3

• Blubber is a dense, vascularised layer of fat reinforced by collagen and elastic fibres
• Occurs in all marine mammals; except for polar bears and sea otters
• Functions as an insulator because it is a poor conductor of heat
• May comprise up to 50% of the body mass of some species at some stages in the life cycle

Question 4

Explain how insulation fur helps mammals maintain their temperature

Answer 4

• Polar bears, pinnipeds and sea otters rely on hair for insulation (some more than others)
• Fur functions by trapping pockets of air among the hairs (air is a poor conductor of heat)
• Fur is a more effective insulator than blubber in air
• However, fur has its limitations in water because it can lose its insulation properties if wetted (unsuitable for diving under pressure and must be kept in good condition)