Skip to main content

Marine Mammals

Marine Mammals
Mammals are the most obvious group of animals on land, but they are relatively rare in marine environments. There are just a few types of mammals whose bodies have become specialized for marine life. Among these are the cetaceans, a group that includes whales and dolphins, porpoises, and dugongs.

Marine Mammal Anatomy

Mammals are warmblooded vertebrates that have hair and breathe air. All females of this group have milk-producing mammary glands with which to feed their young. Mammals also have a diaphragm that pulls air into the lungs and a four-chambered heart for efficient circulation of blood. The teeth of mammals are specialized by size and shape for particular uses.

Marine mammals are subdivided into four categories: cetaceans, animals that spend their entire lives in the ocean; sirenians, herbivorous ocean mammals; pinnipeds, web-footed mammals; and marine otters. Animals in all four categories have the same characteristics as terrestrial mammals, as well as some special adaptations that enable them to survive in their watery environment.

The cetaceans, which include whales, dolphins, and porpoises, have streamlined bodies, horizontal tail flukes, and paddle-like flippers that enable them to move quickly through the water. Layers of blubber (subcutaneous fat) insulate their bodies and act as storage places for large quantities of energy. Their noses (blowholes) are located on the tops of their heads so air can be inhaled as soon as the organism surfaces above the water.

Manatees and dugongs are the only sirenians. These docile, slow-moving herbivores lack a dorsal fin or hind limbs but are equipped with front limbs that move at the elbow, as well as with a flattened tail. Their powerful tails propel them through the water, while the front limbs act as paddles for steering.

The pinnipeds—seals, sea lions, and walruses—are carnivores that have webbed feet. Although very awkward on land, the pinnipeds are agile and aggressive hunters in the water. This group of marine mammals is protected from the cold by hair and blubber. During deepwater dives, their bodies are able to restrict blood flow to vital organs and slow their heart rates to only a few beats a minute, strategies that reduce oxygen consumption. All pinnipeds come onto land or ice at breeding time.

The sea otters spend their entire lives at sea and only come ashore during storms. They are much smaller than the other marine mammals. Even though otters are very agile swimmers and divers, they are clumsy on shore. Their back feet, which are flipperlike and fully webbed, are larger than their front feet. Internally, their bodies are adapted to deal with the salt in seawater with enlarged kidneys that can eliminate the excess salt.

Body Temperature

Animals that are described as warm blooded, or endothermic, maintain a constant internal temperature, even when exposed to extreme temperatures in their environment. In mammals, this internal temperature is about 97°F (36°C), while in birds, it is warmer, around 108°F (42°C).

Warm-blooded animals have developed several physiological and behavioral modifications that help regulate body temperature. Since their bodies generate heat by converting food into energy, they must take in enough food to fuel a constant body temperature. Once heat is produced, endotherms conserve it with insulating adaptations such as hair, feathers, or layers of fat. In extreme cold, they also shiver, a mechanism that generates additional heat.

Heart rate and rate of respiration in warm-blooded animals does not depend on the temperature of the surroundings. For this reason, they can be as active on a cold winter night as they are during a summer day. This is a real advantage that enables warm-blooded animals to actively look for food year round.

The internal temperature of coldblooded, or ectothermic, animals is the same as the temperature of their surroundings. In other words, when it is hot outside, they are hot, and when it is cold outside, they are cold. In very hot environments the blood temperature of some cold-blooded animals can rise far above the blood temperature of warmblooded organisms. Furthermore, their respiration rate is dependent on the temperature of their surroundings. To warm up and speed their metabolism, cold-blooded animals often bask in the sun. Therefore, cold-blooded animals such as fish, amphibians, and reptiles, tend to be much more active in warm environments than in cold conditions.

Popular posts from this blog

Advantages and Disadvantages of an Exoskeleton

More than 80 percent of the animal species are equipped with a hard, outer covering called an exoskeleton. The functions of exoskeletons are similar to those of other types of skeletal systems. Like the internal skeletons (endoskeletons) of amphibians, reptiles, birds, and mammals, exoskeletons support the tissues and give shape to the bodies of invertebrates. Exoskeletons offer some other advantages. Serving as a suit of armor, they are excellent protection against predators. Also, because they completely cover an animal’s tissues, exoskeletons prevent them from drying out. In addition, exoskeletons serve as points of attachment for muscles, providing animals with more leverage and mechanical advantage than an endoskeleton can offer. That is why a tiny shrimp can cut a fish in half with its claw or lift an object 50 times heavier than its own body.
Despite all their good points, exoskeletons have some drawbacks. They are heavy, so the only animals that have been successful with them …

Differences in Terrestrial and Aquatic Plants

Even though plants that live in water look dramatically different from terrestrial plants, the two groups have a lot in common. Both types of plants capture the Sun’s energy and use it to make food from raw materials. In each case, the raw materials required include carbon dioxide, water, and minerals. The differences in these two types of plants are adaptations to their specific environments.
Land plants are highly specialized for their lifestyles. They get their nutrients from two sources: soil and air. It is the job of roots to absorb water and minerals from the soil, as well as hold the plant in place. Essential materials are transported to cells in leaves by a system of tubes called vascular tissue. Leaves are in charge of taking in carbon dioxide gas from the atmosphere for photosynthesis. Once photosynthesis is complete, a second set of vascular tissue carries the food made by the leaves to the rest of the plant. Land plants are also equipped with woody stems and branches that …

Prokaryotic Cell Structure

Prokaryotic cells are about 10 times smaller than eukaryotic cells. A typical E. coli cell is about 1 μm wide and 2 to 3μm long. Structurally, prokaryotes are very simple cells when compared with eukaryotic cells, and yet they are able to perform the necessary processes of life. Reproduction of prokaryotic cells is by binary fission—the simple division of one cell into two cells, after DNA replication and the formation of a separating membrane and cell wall. All bacteria are prokaryotes, as are the archaea.

Embedded within the cytoplasm of prokaryotic cells are a chromosome, ribosomes, and other cytoplasmic particles (Fig. 1). Unlike eukaryotic cells, the cytoplasm of prokaryotic cells is not filled with internal membranes. The cytoplasm is surrounded by a cell membrane, a cell wall (usually), and sometimes a capsule or slime layer. These latter three structures make up the bacterial cell envelope. Depending on the particular species of bacterium, flagella, pili (description follows)…