295
chapter thirteen
Disease
Shawn P. Johnson and Claire A. Simeone
13.1 Introduction
Marine mammals are exquisitely adapted to occupy the niches that they do. Manatees
(Trichechus sp.) have a specialized digestive tract to break down the sea grass they
feed on in both fresh and saltwater. Many species of pinnipeds, which include seals,
sea lions, and walruses, exhibit the unique behavior of spending much of their time at
sea, often migrating long distances, and then all returning to the same site each year
to breed on land.
Some marine mammal species are apex predators, meaning that as healthy adults they
are not usually preyed upon by other species in the wild. Polar bears (Ursus maritimus),
for example, feed almost exclusively on seals and other marine mammals without fear of
other predators. Blue whales (Balaenoptera musculus) only feed on planktonic krill, but they
are considered apex predators as well, as they are at the top of the food chain in their ecosystem. Both marine mammal species help to keep prey populations balanced and keep
the ecosystem healthy.
Contents
13.1 Introduction ........................................................................................................................ 295
13.2 Cetaceans ............................................................................................................................ 296
13.2.1 Physiologic adaptation: Respiratory system ...................................................... 296
13.2.2 Physiologic adaptation: Skin ................................................................................ 297
13.3 Pinnipeds ............................................................................................................................ 298
13.3.1 Physiologic adaptation: Haul-out behavior ........................................................ 298
13.4 Sea otters ............................................................................................................................. 299
13.4.1 Physiologic adaptation: Metabolism ................................................................... 299
13.5 Sirenians ..............................................................................................................................300
13.5.1 Physiologic adaptation: Gastrointestinal tract ...................................................300
13.6 Polar bears ...........................................................................................................................300
13.6.1 Physiologic adaptation: Prey sources ..................................................................300
13.7 Marine mammal populations .......................................................................................... 301
13.7.1 Population example: Neoplasia ........................................................................... 302
13.7.2 Population example: Viral infections .................................................................. 302
13.8 Difficulties of diagnosis .................................................................................................... 302
13.9 Lingering mysteries ........................................................................................................... 303
Glossary ........................................................................................................................................304
References .....................................................................................................................................305
chapter thirteen
Disease
Shawn P. Johnson and Claire A. Simeone
13.1 Introduction
Marine mammals are exquisitely adapted to occupy the niches that they do. Manatees
(Trichechus sp.) have a specialized digestive tract to break down the sea grass they
feed on in both fresh and saltwater. Many species of pinnipeds, which include seals,
sea lions, and walruses, exhibit the unique behavior of spending much of their time at
sea, often migrating long distances, and then all returning to the same site each year
to breed on land.
Some marine mammal species are apex predators, meaning that as healthy adults they
are not usually preyed upon by other species in the wild. Polar bears (Ursus maritimus),
for example, feed almost exclusively on seals and other marine mammals without fear of
other predators. Blue whales (Balaenoptera musculus) only feed on planktonic krill, but they
are considered apex predators as well, as they are at the top of the food chain in their ecosystem. Both marine mammal species help to keep prey populations balanced and keep
the ecosystem healthy.
Contents
13.1 Introduction ........................................................................................................................ 295
13.2 Cetaceans ............................................................................................................................ 296
13.2.1 Physiologic adaptation: Respiratory system ...................................................... 296
13.2.2 Physiologic adaptation: Skin ................................................................................ 297
13.3 Pinnipeds ............................................................................................................................ 298
13.3.1 Physiologic adaptation: Haul-out behavior ........................................................ 298
13.4 Sea otters ............................................................................................................................. 299
13.4.1 Physiologic adaptation: Metabolism ................................................................... 299
13.5 Sirenians ..............................................................................................................................300
13.5.1 Physiologic adaptation: Gastrointestinal tract ...................................................300
13.6 Polar bears ...........................................................................................................................300
13.6.1 Physiologic adaptation: Prey sources ..................................................................300
13.7 Marine mammal populations .......................................................................................... 301
13.7.1 Population example: Neoplasia ........................................................................... 302
13.7.2 Population example: Viral infections .................................................................. 302
13.8 Difficulties of diagnosis .................................................................................................... 302
13.9 Lingering mysteries ........................................................................................................... 303
Glossary ........................................................................................................................................304
References .....................................................................................................................................305