Skip to main content

Sharks on the Coral Reef

Zebra sharks (Stegostoma fasciatum) have black and white stripes when they are young but lose the stripes and develop spots as adults. These solitary night hunters have very flexible bodies and can swim into tight places to search the cracks and crevices of the reef for small fish, snails, and clams and other mollusks. During the day, they rest on sandy ocean floor near the reef, lying with their mouths open and facing the currents to keep water flowing over their gills. The adults reach lengths of 10 feet (3.1 m).

Zebra sharks (Stegostoma fasciatum)
Zebra sharks (Stegostoma fasciatum)

An easily identifiable reef animal is the nurse shark (Ginglymostoma cirratum), a species that is distinguished by skin flaps on the nose and barbels on the chin. This docile, unaggressive bottom feeder rests on ledges and in caves. When feeding, a nurse sharks sucks up its food by creating a vacuum that pulls the prey into its mouth. Some of this shark’s favorite foods are mollusks and crustaceans, which it crushes with rounded teeth. Adult nurse sharks can reach lengths of 8 feet (2.4 m).

nurse shark (Ginglymostoma cirratum)
Nurse shark (Ginglymostoma cirratum)

The blacktip reef shark (Carcharhinus melanopterus) has a white flash on its side and a black tip on its tail. Active swimmers and aggressive hunters, blacktips work together to round up schools of fish into compact groups before attacking in a feeding frenzy. These sharks grow to be about 5 feet (1.5 m) long. In contrast, the whitetip reef shark (Triaenodon obesus) is very docile, spending the day lying beside other whitetips in a cave or on a ledge. These animals feed at night, moving around the reef shyly, hunting octopuses, lobsters, crabs, and small fish on the floor of the reef. The 5-foot (1.5-m) long animal can easily be identified by the white markings on the tips of their fins.

reef shark (Carcharhinus melanopterus)
Reef shark (Carcharhinus melanopterus)

A Japanese wobbegong shark (Orectolobus japonicus) may be difficult to spot on the reef. This quiet animal has splotchy skin that camouflages it against the reef’s soil and rocks. The wobbegong lies patiently on the bottom, grabbing prey that unwittingly swim too close. The shark grasps its chosen meal in daggerlike teeth, letting it squirm till exhausted. Then the wobbegong turns the prey so that it can be swallowed headfirst, a technique that keeps the victim’s fins from getting caught in the shark’s throat.

Orectolobus japonicus
Orectolobus japonicus

The reef’s smooth hammerhead shark (Sphyrna zygaena) is one of 10 species of hammerheads, all of which have flattened projections at the sides of their heads. The shark’s eyes are mounted on the outer edges of the head lobes, and their nostrils are set far apart. Hammerheads can grow to lengths of 14 feet (4.3 m), and they aggressively hunt fish and rays, although they will scavenge, too. In the summer, groups of hammerheads may migrate to cooler water.

hammerhead shark (Sphyrna zygaena)
Hammerhead shark (Sphyrna zygaena)

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)…