The world of coral reefs contains one of the most diverse environments on our planet, supporting more species per square meter than any other ocean ecosystem. Because of this phenomenal diversity, coral reefs are sometimes called the rainforests of the sea. From the microscopic to the gigantic, coral reefs support and nurture a tremendous variety of creatures.
These reef systems have been built up over thousands of years by tiny calcium-
producing organisms. The reefs are a haven for countless forms of life, some of which seem totally alien in form. It is a “Star Wars” world of bright colors, ever changing patterns and odd shaped creatures that look as though they came directly from central casting. Only on the coral reef can one find living examples from nearly every group of organisms.
Scuba Diving on a coral reef gives you some idea about what it would be like to explore another planet. Drifting weightless across this diverse landscape enables you to appreciate some of the tremendous complexity and simplicity that makes up the coral reef. Man has spent a relatively modest effort scientifically exploring the world’s oceans compared to the time and money that has gone into exploring the surface of the Moon and other planets. Yet, the growing and ongoing exploration of our oceans continues to bring the discovery of new species, the identification of different environments where marine life flourishes and a little more understanding of our underwater world. It is a place of never-ending wonders.
The world of the coral reef is also an extremely fragile environment, and it is under considerable pressure and facing real dangers to its continued existence. The distress and destruction of coral reefs has a noticeable impact on our lives from the foods we eat to the air we breathe. From the Florida Keys to the Great Barrier Reef in Australia, to the atolls of the Pacific and islands of the Indian Ocean our coral reefs need our help. If we wish to leave a healthy and thriving reef system to our children and their children we need to understand the threats to this amazing environment and understand actions that can be taken to preserve and restore our reefs. These are our oceans and the first step to helping protect coral reefs is education.
This segment provides a high-level overview of the basic types of creatures found on the coral reefs, including:
- Corals and Anemones
- Sea Worms
- Sharks and Rays
- Marine Reptiles
- Marine Mammals
Come join us as we “dive into” this amazing and mysterious world.
Sponges, though extremely plant-like in appearance, are actually one of the simplest of multi-cellular animals. They belong to a group called porifera which means pore bearer.
Sponges differ from all other marine invertebrates in that they have no true tissues or organs. They have unspecialized cells and do not have nervous, digestive or circulatory systems. Their structure is composed of simple aggregations of cells. The tissue of sponges encloses a vast network of chambers and canals that connect to the open pores on their surface. Sponges rely on maintaining a constant flow of water through their bodies to obtain food, oxygen and remove wastes. They feed by drawing a current of water in through their pores, filtering out the nutrients, and then ejecting it out through an opening. The tiny pores, called ostia lead internally to a system of canals and eventually out to one or more larger holes, called oscula.
Sponges can be found in an infinite variety of colors and shapes and while most sponges are relatively small, some varieties, such as the Giant Barrel Sponge, can grow to over 6 feet in diameter. Many sponges on the coral reef resemble corals in shape and color
and are one of the many life forms unique to the ocean environment.
Sponges are a diverse group of sometimes common types, with about 8,000 species known across the world. Sponges live primarily in marine (ocean) environments, but around 150 species live in fresh water. Sponges live in a wide variety of environments from Polar Regions to the tropics and from tidal zones to depths exceeding 8,800 meters (5.5 mi).
Coral and Anemones
Although many people mistake corals and anemones as plants, they are actually animals. They are part of a simple group of animals known as cnidaria. Jellyfish are also a member of this group. These animals are characterized by a symmetrical body, usually with stinging tentacles, and a central mouth. A coral reef is composed of hundreds or thousands of these tiny animals growing together as a colony. Their tiny calcium shells have accumulated over thousands of years to form the largest living structures in the world. The majority of the cnidaria live attached in colonies in
the form of reefs (Hydrozoans), but a few are free swimming like the jellyfish (Scyphozoans). Most of these animals use special stinging cells called nematocysts to catch their prey. A few of them, particularly the jellyfishes, are capable of inflicting extremely painful stings on humans. The anemones are well known for establishing a symbiotic relationship with members of the clownfish family. This is a special living arrangement where both animals work together to benefit each other. The anemone provides protection for the clownfish, and the clownfish in turn provides food for the anemone.
Cnidarians are diverse in their habitat and are distributed throughout all of the world’s oceans, in polar, temperate and tropical waters. They can be found in a variety of water depths and closeness to shore from shallow, coastal habitats to the deep sea. While coral reefs are more often found in tropical and sub-tropical water within the latitudes of 30 degrees north and 30 degrees south, there are many deep water corals that live in colder regions.
The sea worms are a large and varied group of and are found in several different phyla, including the Platyhelminthes, Nematoda, Annelida (segmented worms), Chaetognatha, Hemichordata, and Phoronida. In the ocean, however, the worms have many different appearances. One of the more interesting
varieties is the tube worms. These animals form a hard-shelled tube that provides them protection. The feather duster worms have a series of feathery tentacles on top that are used to filter nutrients from the water. When threatened by predators, they quickly withdraw deep into their tube homes. Another species, the Christmas tree worm, has a very ornate arrangement of feeding tentacles that can be found in a wide variety of bright colors. Some sea worms, such as the bristle worm, wander the sea floor with a covering of tiny bristles that can deliver a painful sting if threatened. Flatworms have flattened bodies and look more like chewing gum as they forage for food on the rocks.
Marine worms are found around the world and in all oceans, from colonies that live in tidal flats to trench environments in depths exceeding 4,000 meters.
The Echinoderms are a group of animals that includes starfish, urchins, feather stars,
and sea cucumbers. They are simple animals, lacking a brain and complex sensing organs. Echinoderms are characterized by their radial symmetry and a central mouth. Although a sea urchin looks round, closer inspection reveals that it is nothing more than a starfish with its legs wrapped inwards to form a sphere. The echinoderms are found in a stunning variety of shapes and colors, and are found decorating coral reefs around the world. Some of these animals are carnivorous, feeding on corals and scavenging the ocean floor. Certain species of starfish actually extend their stomachs into their unwary victims in order to digest them. The feather stars and sea cucumbers are mainly filter feeders, catching what ever they can find floating in the ocean currents. All of the echinoderms move around with the use of thousands of tiny tube feet, many of which have suction cups on the ends. Many of the urchins have developed extremely sharp spines as a means of protection. It is estimated that there are around 7,000 living species of Echinoderms.
Echinoderms are found in almost all depths, latitudes and environments in the ocean. They reach the highest density levels in coral reef environments but are also widespread on shallow shores and around the poles. They occur in various habitats from the intertidal zone down to the bottom of the deep sea trenches and from sand and rubble to coral reefs and are in cold and tropical seas.
The world of the crustaceans is a world of bizarre shapes and adaptations. This group of animals is probably best known for their hard outer shell. As the animal grows, this shell must be removed and discarded. Once this takes place, the new shell takes time to harden. During this period, the animal is without its primary means of protection and vulnerable to attack from predators. But they have an impressive arsenal of weapons at their disposal. The claw of many crustaceans is capable of
exerting hundreds of pounds of pressure. Some even have the unique ability to produce a deafening miniature sonic boom with which they stun their prey. The mantis shrimp can even break the glass of an aquarium or split a man’s thumb to the bone with one strike. But in spite of their impressive armor and fierce weaponry, the crustaceans do occasionally meet their match. The teeth of the triggerfish and the beak of the octopus can crack through the toughest shells of crabs and lobsters, making an enjoyable meal.
Crustaceans are found in the seas at all depths and ranges from cold water to the tropical environments.
Mollusks comprise a group of soft-bodied animals that includes snails, clams, and sea slugs. The most common characteristic of most mollusks is their shell. One of the largest groups, the snails, is renowned for their shells. Snails are univalves, which means they have one shell. And it is this shell that for many people is the epitome of the ocean. There is perhaps no other ocean treasure that displays more diversity and beauty than the shell. Conchology, the study and collection of shells is a popular hobby the world over. The bivalves, or two-shell mollusks include the clams, scallops, and oysters. It is the oyster that is responsible for producing the most coveted of the
ocean’s treasures – the pearl. Still other mollusks have lost their shells altogether. The octopus, the squid, and the sea slugs have their own survival strategies and weapons instead of protective armor. The octopus, in fact, has the largest and most complex brain of all the mollusks. There are approximately 85,000 recognized species of mollusks with Gastropods comprising about 80% of the total number of species.
Marine Mollusks are found worldwide from intertidal habitats to the deepest oceans.
By far one of the most colorful and diverse groups of animals in the sea is that of the coral reef fishes. Their extensive range of bright colors and bold patterns is virtually unmatched in the entire undersea kingdom. And although they may be beautiful to behold, there is a real function behind each of these designs. Red colors appear black under water, helping a fish to go unseen. Stripes allow a fish to camouflage itself against the coral. Spotted patterns serve to confuse a would-be predator. Each species of fish deals with survival in its own way, and we are left to wonder at their accomplishments. The term “fishes” is used when referring to many different species
at once and the word “fish” is used when talking about members of the same species or members of a single group. Fish are a diverse group of animals that include bony fish and cartilaginous fish.
Perhaps nowhere else on Earth has so many strange and unusual adaptations taken place. The coral reef is a showcase for these bizarre creatures. Fishes here have many different shapes, sizes and abilities. There are fishes here that do not even look like fish. There are the eels, long skinny fish that look more like snakes. There are pufferfish that actually expand like balloons to avoid being eaten by predators. There are the seahorses, which are one of the most unusual fish designs on the reef. And believe it or not, it is actually the male seahorse that gives birth to the young. There are even seahorses that look like seaweed. Camouflage has evolved into an art form here on the coral reef. There are fishes that look like rocks and fishes that look like plants. Even
experienced divers can be fooled by some of these ingenious disguises. The art of poison has also reached new heights on the reef. Many undersea residents have strong poisons as a means of protection. Some species carry enough venom in their bodies to kill several men.
Fishes are found around the world from altitudes of more than 5,000 m (3 mi), as in Lake Titicaca, located 3,800 m (2.3 mi) above sea level in the Andes, to depths of about 10 km (6 mi) in the Pacific Ocean. Some, like certain killifishes, Cyprinodon, inhabit hot springs, where the water temperature may reach 45 deg C (113 deg F); others, like the icefishes, Chaenocephalus, are found in Antarctic seas, where water temperature may fall below 0 deg C (32 deg F). About 107 species, including the swordfish, Xiphias, are distributed worldwide in tropical and subtropical waters, but many species have very limited ranges, among the smallest being that of the Killifish Cyprinodon diabolis, which is confined to a single spring in Nevada.
It is estimated that there are about 20,000 or more species of fishes with about 60%
living in marine environments and 40% living in fresh water. Most of the world’s fishes are continental in orientation, living either as part of the freshwater systems on land or as sea-dwellers staying near and influenced by the coastal environment. High densities of marine fish populations occur near coasts, because the waters there are extremely rich in nutrients.
Sharks and Rays
There is perhaps no other animal on Earth that evokes more fear in the mind of man than the shark. They are viewed as vicious man-eaters and are slaughtered the world over in an attempt to make the seas safe. But of the hundreds of different species of sharks in the ocean, only a small handful pose any threat to man. Humans do not appear to be on the menu for sharks. It is thought that most shark attacks are a case of mistaken identity. A diver in a wet suit looks a lot like a sea lion, a favorite food for some of the larger sharks. The fact is that more people are killed by lightning each year then by sharks. Public fear and ignorance of these magnificent animals has led to many species being hunted and killed in large numbers. They have almost disappeared in some parts of the world.
Sharks are one of the most efficient and effective hunting machines in the animal
Sharks and rays are adapted for a wide range of aquatic habitats from tropical and temperate seas as well as some cold and polar seas. Various species inhabit shallow coastal habitats, deep-water ocean floor habitats, and the open ocean.
Reptiles, including turtles, lizards, snakes and crocodilians are not the most common residents of the coral reef, but they are definitely among the most beautiful. Perhaps the most well known reptiles in the sea are the turtles. There are many different species of sea turtle, ranging in size from only 2 feet to the real giants at over 6 feet in length. Sea turtles lay their eggs on land. They can be seen on the beaches late at night digging a deep hole in the sand. The eggs are deposited and covered over. Several months later, the tiny turtles dig their way to the surface and scramble towards the sea. But a
turtle’s life is not easy. Only one in a thousand will survive the predators and return to the beach one day. Sea turtles were once killed by the thousands for food. Today, even though many face extinction they continue to be exploited. Their eggs and shells are in constant demand the world over.
Another member of the sea reptile family enjoys full protection. The sea snake is the most venomous snake on Earth. Several sea snake species can be found swimming the world’s coral reefs. Some of them are spectacularly colored. Divers are weary of this animal, but the sea snake is timid and will not attach unless provoked.
All reptiles live in warm tropical and subtropical environments and include about 80 species and sub-species of sea snakes, seven sea turtle species, the saltwater crocodile and the Galapagos Marine Iguana. Each of these groups has unique characteristics and adaptations for life in the ocean, but all must return to the surface to breathe air. Most marine reptiles must spend at least part of their life cycle in terrestrial environments to reproduce.
Most of these animals include seals, whales, dolphins, and walruses and form a diverse group of 128 species that rely on the ocean for their existence. The are comprised into four groups the cetaceans, which includes the dolphins and whales, the pinnipeds, which includes the seals and sea lions, the sirenians (manatees and dugongs), and fissipeds, which are the group of carnivores with separate digits (the polar bear, and two species of otter). Breathing air and then diving, cetaceans can hold their breath for unimaginable lengths of time. They are peaceful animals, and they are quite intelligent. Some of the largest brains in the world of mammals are found in the oceans. These animals have exhibited remarkable abilities to communicate and learn. Their natural lives are spent in close family groups caring for their young and each other. Their songs can be heard echoing for miles beneath the waves. Many of these magnificent animals were hunted to the brink of extinction. But today, under the protection of most of the world’s governments, they are coming back. In marine parks around the world, their ambassadors are helping to save their
kind by helping us to better understand them.
Marine mammals are widely distributed throughout the globe, but their distribution is patchy and coincides with the productivity of the oceans. Species richness peaks at around 40° latitude, both north and south.
- What are Coral Reefs
- Introduction to the Underwater World
- Creatures of the Coral Reef
- Manta Rays, Silent Sentinels of the Sea
Stay tuned for more information on the amazing world of our Coral Reefs. The pool is open…