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Showing posts from April, 2013

Marine Bird Anatomy

Birds are warm-blooded vertebrates that have feathers to insulate and protect their bodies. In most species of birds, feathers are also important adaptations for flying. As a general rule, birds devote a lot of time and energy to keeping their feathers waterproof in a process called preening. During preening, birds rub their feet, feathers, and beaks with oil produced by the preen gland near their tail.
The strong, lightweight bones of birds are especially adapted for flying. Many of the bones are fused, resulting in the rigid type of skeleton needed for flight. Although birds are not very good at tasting or smelling, their senses of hearing and sight are exceptional. They maintain a constant, relatively high body temperature and a rapid rate of metabolism. To efficiently pump blood around their bodies, they have a four-chambered heart.
Like marine reptiles, marine birds have glands that remove excess salt from their bodies. Although the structure and purpose of the salt gland is the s…


Birds, vertebrates of the class Aves, are the second largest group of vertebrates on Earth, following fish. Unlike marine reptiles, seabirds do not actually live in the water; however, they depend on the sea for their food, and their bodies are highly specialized for aquatic life. Many of the seabirds who feed on animals in the coral reefs also spend some of their time in other marine areas. All of them go to shore during parts of their lives, and some migrate from one ocean area to another.
Seabirds are among the longest-lived birds in the world, many with life spans of 30 years or more. For these animals, reproducing is a serious investment of time and energy. Compared to terrestrial avians, seabirds produce fewer offspring and the young are slower to mature, taking an average of seven years. Many choose their mates for life, and the males and females work together to incubate the eggs.
There are many species of birds that nest near coral reefs and interact with the reef food webs. …

Marine Reptile Anatomy

Reptiles are not usually associated with marine environments. In fact, of the 6,000 known species of reptiles, only about 1 percent inhabits the sea. Members of this select group include lizards, crocodiles, turtles, and snakes. Each of these organisms shares many of the same anatomical structures that are found in all reptiles: They are cold-blooded, air-breathing, scaled animals that reproduce by internal fertilization. Yet, to live in salt water, this subgroup has evolved some special adaptations not seen in terrestrial reptiles.

In turtles, the shell is the most unique feature. The lightweight, streamline shape of the shell forms a protective enclosure for the vital organs. The ribs and backbone of the turtle are securely attached to the inside of the shell. The upper part of the shell, the carapace, is covered with horny plates that connect to the shell’s bottom, the plastron. Extending out from the protective shell are the marine turtle’s legs, which have been modified into padd…

Marine Reptiles

Among the reptiles, only a small number of species have become adapted for life in the sea. Of these, just a few are fulltime reef residents. Reptiles frequently found around reefs include the sea turtles and sea snakes.
Sea turtles move through the water with the grace of ballerinas. These large reptiles, related to the more familiar but generally smaller land turtles, are superbly adapted for sea life. Their limbs are modified as strong flippers that effortlessly push their streamlined bodies through the water.
Turtles are such expert swimmers and so perfectly designed for their lifestyles that it would be easy to think of them as big fish; however, unlike fish, turtles must swim to the surface to breathe. These animals have lungs instead of gills, and they breathe through their noses. Even though active turtles need to surface every few minutes, they are capable of staying under water for long periods of time by holding their breath. When resting in caves or on ledges, sea turtles m…

Coral reef communities

Coral reef communities support a larger number and greater diversity of fish than any other aquatic habitat. Reef fish are specialized for a variety of feeding strategies and habitats, adaptations that permit different species to feed within the same area and on similar food supplies. Damselfish, for example, primarily feed on algae that grow on top of the coral skeletons, but parrot fish prefer the algae within the coral polyps.
Many reef fish are predators of fish or invertebrates. Even though the most impressive hunting fish are large, there are an equal number of smaller, less obvious ones. Hunters patrol the area day and night, even at dusk and dawn when fish are moving to their refuges.
A good number of reef fish are plankton eaters, including soldierfish and cardinals. Plankton feeders are not closely related to one another but share similar lifestyles. Usually they have small, streamlined bodies and forked tails, which are good at delivering bursts of speed to escape predators.…


Fish living close together may show territorial behavior, the tendency to occupy and defend an area, usually to eat and reproduce there. There are many different patterns of territorial behavior. Some species are territorial all the time, but others may only display this behavior during reproductive periods. Depending on the situation, fish may be territorial against their own species, toward other species, or both.
Territorial behavior requires a lot of energy, and a fish cannot afford to expend more energy on defending its territory than it takes in as food. For this reason, fish have developed several threatening displays that involve
a lot of posturing and ritualized motions yet conserve energy. If an intruder gets close to a damselfish’s alga garden, for example, the damselfish first attempts to scare it away with a threatening posture of spread fins and gill covers. If this strategy does not solve the problem, the damselfish makes excited, aggressive movements. Only as a last res…


Fish often school, or swim together, in large groups. Schools of fish may be polarized, with all the fish swimming in the same direction, or non-polarized, with fish swimming in many directions. Both types of schools improve an individual fish’s chance of survival. A large school of fish may be able to confuse a predator into thinking that it is one big, dangerous organism instead of a group of small, helpless fish. In addition, if a fish is in a school, it stands a good chance of being spared when a predator does attack. Plus, a school of fish has more lookouts than one fish swimming alone, and is more likely to notice danger.

Some kinds of fish, such as groupers, only form schools when it is time to spawn. This strategy ensures that the males and females will release their gametes into the water at the same time. If egg predators are nearby, they will eat some of the eggs but may not be able to eat all of them, so some will probably survive. Foraging for food can also bring a group…

Sea Horses, Surgeonfish, and Remoras

Sea horses and their close relatives, the pipefishes and sea dragons, have a distinctive appearance. Unlike other bony fish, the elongated bodies of these animals are supported by rings of bone. All of these fish feed through tubelike mouths that suck in small crustaceans and other prey. Instead of chasing their food, they quietly hover in the water and wait for something edible to swim by.
A sea horse, swims upright among the corals or sea grasses, moving slowly from one perch to another. To keep from drifting away, a seahorse may hold in place by wrapping its prehensile tail around a plant or piece of coral. Pipefish and sea dragons swim like other kinds of fish, with their heads leading. A pipefish has a long, thin shape, so it resemble grass or reeds. In contrast, sea dragons are covered in leaflike appendages that help camouflage them as they float in beds of leafy seaweeds.
 In all groups, the males take care of the eggs. After eggs form in the female’s body, they are transferre…

Grunts, Wrasses, Gobies, and Flounders

A reef is a pretty noisy place to live. One family of fish, the grunts, get their name from the grunting noise they make by grinding their pharyngeal teeth. Grunts are pretty, deep-bodied fish that are generally found traveling in schools. The French grunt (Haemulon flavolineatum) has yellow stripes on a silver background or blue stripes on orange.
Wrasses are a large group of fish that are well represented on the reef. Most are small, averaging about 9 inches (23 cm) long, with cigar-shaped bodies, pointed snouts, and prominent canine teeth. During the daytime wrasses feed, and at night they hide in crevices or buried in sand. Wrasses feed in several ways, depending on their species.
 The cleaner wrasses remove mucus, parasites, and scales from the bodies of larger fishes. Another species exhibits “following behavior” to find prey. As larger fish swim through the substrate and disturb it, these wrasses follow closely, picking up invertebrates that the large fish overlook. A differen…

Scorpion Fish, Catfish, and Eels

Another fish that depends on camouflage is the scorpion fish (family Scorpaenidae), a heavy animal with ridges and spines on its back. The fins and spines contain venom that protects this fish from predators. Warts and skin tassels covering its body make the scorpion fish look like part of the reef. This animal waits patiently for prey to get close then literally sucks it in.
The bandtail puffer (Spheroides spengleri), like other species of puffers, has a very different way of protecting itself. By filling its abdomen with water, the little fish can inflate its body, giving it a bigger and fiercer appearance. In addition, an inflated fish is more difficult for a predator to swallow than an uninflated one. A close relative, the porcupine fish (Diodon hystix), uses the same mechanism when it feels threatened. Porcupine fish are covered with damaging sharp spines that deter predators. Shallow reef waters and turtle grass beds are some of the places where porcupine fish hunt for prey. Bot…

Damselfish, Clown Fish, Cardinal Fish, and Squirrelfish

Another colorful and abundant reef fish is the damselfish, a delicate-looking animal with a small mouth. Damselfish nibble on the encrusting algae that grow on coral and rock. These red, yellow, orange, or blue fish grow to be about 6 inches (15 cm) long.

Like most damselfish, the Pacific gregory (Stegastes fasciolatus) is active during the day. Most of this fish’s time is spent “farming” a patch of alga that may cover up to 10.7 square feet (1 sq. m) of the reef. An excellent gardener, the little damselfish weeds out unwanted corals and algae so that its favored algae can flourish. To supplement plant growth, the fish fertilizes its garden with its own feces.

One of the brightest and best-known reef fish is the percula clown fish (Amphiprion ocellaris), one of several species of clown fishes and a member of the damselfish family. Reaching only 2.4 inches (6 cm), this small animal is striped in orange, white, and black. The percula clown fish lives in the tentacles of several kinds o…

Bony Fish Anatomy

All bony fish share many physical characteristics, which are labeled in Figure below. One of their distinguishing features is scaly skin. Scales on fish overlap one another, much like shingles on a roof, protecting the skin from damage and slowing the movement of water into or out of the fish’s body.
Bony fish are outfitted with fins that facilitate maneuvering and positioning in the water. The fins, which are made of thin membranes supported by stiff pieces of cartilage, can be folded down or held upright.
Fins are named for their location: Dorsal fins are on the back, a caudal fin is at the tail, and an anal fin is on the ventral side. Two sets of lateral fins are located on the sides of the fish, the pectoral fins are toward the head, and the pelvic fins are near the tail. The caudal fin moves the fish forward in the water, and the others help change direction and maintain balance.
Although fish dine on a wide assortment of food, most species are predators whose mouths contain small…

Bony Fish

More than 90 percent of the world’s fish have skeletons made of bone instead of cartilage. Bony fish appear in all sizes, shapes, and colors imaginable. They can be as small as guppies, or as massive as an 880-pound (400-kg) tuna. Some are shaped like bullets, some like pencils, and others like flat plates. On the reef, bony fish display a rainbow of colors and an almost endless variety of markings.

When people envision a coral reef fish, most think of parrot fish. These large, brightly colored animals have teeth that are fused to form a parrotlike beak, giving them their name. They are usually found feeding in shallow reef water where they scrape off alga that is growing on top of the coral skeletons, or chew up the skeletons to get to the algae within. Since skeletal material is extremely hard, the digestive systems of parrot
fish have developed unique adaptations to handle it. Teeth in their throats grind the calcium carbonate and release the algae. The algae travel on through the …


One of the most striking features of fish is their colorization. Coloring and body marks on fish help them avoid predators by staying out of sight. Many prey species, such as gulf flounder, avoid being eaten by blending in with their surroundings, matching the subtle shades of their habitats. Spotted fish look like the seafloor, and striped fish blend in with grasses. Some reef fish display bright colors because they live among brightly colored sponges and corals.

Conversely, coloring that mimics fish’s habitats helps predators get close to their prey. The ability to avoid detection is a significant advantage for such hunters as scorpion fish that wait quietly until prey comes within striking distance. A hunter is able to conserve both time and energy if it does not have to pursue its food. Most fish, including sea trout and grouper, display some degree of countershading.
This form of coloring reduces the clarity of the fish’s body outline in water. The simplest, and most common, form…

Skates and Rays

Nicknamed the “pancake sharks,” skates and rays have a lot in common with their cartilaginous cousins; however, their outward appearances are quite different from those of sharks. The bodies of skates and rays, such as the blue-spotted stingray in Figure below, are broad and flattened instead of torpedo-shaped, as in sharks, and the gill slits of skates and rays are located under the body. Skates and rays feed on shallow, sandy reef flats where they can pin down their prey with their winglike fins. When not feeding, they often lie on the bottom to rest. For protection, many species possess one or more poisonous spines on the upper surface of their tails.

The southern stingray (Dasyatis americana) is usually inactive during the day but hunts most of the night by moving over the bottom of the reef. To uncover prey, it spews jets of water from its mouth into the sediment, or stirs up the sand and silt by vigorously flapping its pectoral fins. Once food is located, the ray lifts its body …

Shark Senses

Humans have five senses—sight, smell, taste, touch, and hearing—that help them gather and interpret information about their environment. Sharks have these senses as well as others (see Figure below). Of their five basic senses, smell plays the largest role, and hearing plays the smallest. Sharks smell by detecting molecules in the water, similar to the way air-breathing vertebrates detect odor molecules. The sense of smell in sharks is so keen that they can distinguish one drop of blood in 25 gallons (115 l) of water. Some species have sensory barbels near their mouths that can pick up tastes in the seawater. After a shark senses prey, it homes in by traveling up the prey’s “smell corridor,” moving side to side to read clues in the water. As the shark gets closer, the corridor of clues narrows. Once the prey is found, the shark grabs it, unhinging its jaw if necessary to get its mouth around large animals. Since prey thrash around and can injure their attackers, some sharks have spec…

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).

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 o…

Shark Anatomy

Although there are many kinds of sharks, they all are similar anatomically. A shark’s digestive system begins at the mouth, which is filled with teeth. Shark teeth are continuously produced, and at any time a shark may have 3,000 teeth arranged in six to 20 rows. As older teeth are lost from the front rows, younger ones move forward and replace them. Teeth are adapted to specific kinds of food. Depending on their species, sharks may have thin, daggerlike teeth for holding prey; serrated, wedge-shaped teeth for cutting and tearing; or small, conical teeth that can crush animals in shells.
The internal skeletons of sharks are made of cartilage, a lightweight and flexible bonelike material. Their external surfaces are very tough and rugged. Sharks have extremely flexible skin that is covered with placoid scales, each of which is pointed and has a rough edge on it. Shark fins are rigid and cannot be folded down like the fins of bony fish.
Like other aquatic organisms, sharks get the oxygen…

Sharks and Rays

Fossil evidence shows that early fish, the ancestors of today’s bony fish, had skeletons made of cartilage. Today, the only fish that still have cartilaginous skeletons are the skates and rays. These two groups of primitive fish are closely related.
Several species of sharks and rays are attracted to the bounty of food that the reef has to offer. Although these types of fish have reputations as dangerous creatures, most are fairly shy and not aggressive toward humans. Like other reef residents, skates and rays spend their days looking for food. Because they have few predators, these two groups of animals do not invest much energy in defensive behaviors.

Fish A Rainbow of Colors

The most active and obvious living things in the ocean are the fish, and the greatest diversity of fish species can be found on the coral reef. No other part of the marine environment can match the abundance and diversity of the reef fish populations. Some families of fish are adapted for life among the corals, while others are better suited to live among sea fans, sponges, and sea anemones. Many are specialized to live on the reef floor, while others makes their homes near the water’s surface. The variations in reef fish are almost limitless.
Unlike the reef-building corals, armored crustaceans, and two-shelled clams, fish are vertebrates, animals with backbones. All vertebrates have internal skeletons for structure and support. The skeleton may be made of cartilage, a tough, flexible material; bone; or a combination of the two. Fish are vertebrates that have scales, fins, and gills.
The reef ecosystem can support large populations of fish because most of the inhabitants are specializ…

Marine invertebrates

Coral reefs are the largest structures on Earth that are built and inhabited by invertebrates. Created by a few species of calcium carbonate–secreting organisms, a reef provides homes for thousands of other kinds of animals. The interactions between individuals in this highly diverse group of organisms regulate the ebb and flow of life in reef communities.
Marine invertebrates that live on land are relatively small animals, but some species in the sea grow to spectacular sizes. The giant clam weighs up to a half ton, exceeding the size and weight of any terrestrial cousin. This startling difference in size is due to the advantages that marine environments have over terrestrial ones, especially for invertebrates with shells. The seafloor is a very stable environment, with few changes in physical factors such as light, temperature, and acidity. This constancy facilitates stable conditions within the animals’ tissues. In addition, the water gives structural support to animals, reducing t…