The Coral Ecosystem and How It Is Changing

Coral reefs are one of nature’s most magnificent creations, filled with thousands of unique and valuable plants and animals. More than one quarter of all marine animals is dependent on coral reefs. Coral reefs are also a source of food and income for millions of people too. The coral reef ecosystems benefit humans commercially, recreationally and environmentally. Because of the complex interconnections between coral reefs, mangrove forests, sea grass beds, and many other different plants and animals, coral is very susceptible to destruction. One small change in any of these things can affect mass quantities of coral. That is why it is important to educate people about coral and how complex of a species they really are. That is the purpose of this report, to educate you and make you aware of that complexity.

Coral is often mistakenly identified as a rock, but in all actuality, it is an animal. The actual coral is composed of small animals called coral polyps. Most polyps are very small, although rare species can grow quite large. One coral branch or mound is composed of thousands of polyps. These thousands of polyps are called a coral colony. Polyps are nocturnal and stay inside their skeletons during the day. However, at night they can be seen when they stick their tentacles out to feed.

Corals reproduce in many different ways. Some species are hermaphrodites, and produce both sperm and eggs, and some are single sexed organisms. They can reproduce both sexually or asexually. In most species, the egg and sperm are released into the water and random fertilization occurs. This is called coral spawning. The larva is attracted to the light and swims to the surface of the water where it remains for weeks. If the larva can survive without being eaten by predators, it will sink back to the bottom of the ocean floor. Hear it will attach itself to a hard substrate and will grow into a coral polyp. At this point, the coral polyp begins to reproduce asexually. As new polyps are built and added a colony develops. Eventually the coral colony matures and begins to reproduce sexually again, adding to the ever-continual cycle of life. One of the most amazing aspects of coral reproduction is that of mass coral spawning. In many parts of the world, on the same night of the year, every coral will spawn at the same time. Millions of eggs and sperm are released into the water on the same evening in one of the most beautiful events that occurs in nature.

Coral reefs are massive limestone structures that are home for more than a quarter of all marine life. As one of the most complex ecosystems on the planet, coral reefs are home to over four thousand different species of fish, more than seven hundred species of coral, and thousands of other plants and animals. The reef is actually built by the coral, but not all coral species build reefs. The most active builders on the coral reefs are hard corals. As the polyps of stony corals grow, limestone for their skeletons is produced. When these polyps die, their skeletons are left and are used as a solid substrate for new polyps, which then build more skeletons over the old ones. The actual coral mound or coral tree is made up of thousands of layers of dead coral polyps covered by a very thin layer of living polyps.

Coral reefs are divided into four different classes: fringing reefs, barrier reefs, atolls and patch reefs. Fringing reefs are the most common type of reef. They grow near the coastline around islands and continents. They are separated from the shore by narrow, shallow lagoons. Barrier reefs grow parallel to the coastline. At their shallowest point they can reach the water’s surface forming a barrier to ships trying to sail through them. The most famous example of a barrier reef is the Great Barrier Reef in Australia. It is the largest barrier reef in the world. Atolls are rings of coral that create a protective circle around a lagoon. Atolls are formed around active volcanoes. Over time the volcano sinks into the sea leaving the coral reef. The reef continues to grow after the volcano is gone. This leaves a reef out in the middle of the ocean with a lagoon in the middle of it but no other land surrounding it. Patch reefs are small, reefs that grow up from the bottom of the ocean on an island or a continental shelf. They most commonly can be found between fringing reefs and barrier reefs. They vary greatly in size, and will hardly ever reach the surface.

Coral reefs have partnerships with other species that are often nearby reefs. Mangrove forests, sea grass beds, and nearby beaches all affect the growth of the reefs. Human interaction with any of these partners can have a drastic affect on the reefs. Mangrove forests can be found along muddy beaches and have several very important functions for coral reefs. They act as nurseries for young fish and other coral animals.