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What Is A Coral?

Despite the fact that corals look more like rocks or plants, they are definitely animals. Coral colonies are composed of many tiny, cup-shaped animals called polyps, which are related to jellyfish. A single coral polyp may be as large as a saucer or smaller than the head of a pin. Millions of polyps working together in a cooperative colony generation after generation create the limestone skeletons that form the framework of the beautiful coral reef.

How Do Corals Start Out Life?

Corals begin life in tropical waters as free-floating larvae. After a relatively short period of time, the larva eventually attaches itself to a hard surface and becomes a polyp. Polyps divide asexually and form colonies. Coral colonies reproduce both sexually and asexually. In sexual reproduction, the coral polyps release both eggs and sperm into the water. (This is also known as coral spawning.) One type of asexual reproduction occurs when fragments of coral are broken off as a result of storm action. The broken pieces of corals usually survive and continue to grow and produce a new colony. This process is referred to as “fragmentation”.

What Do Corals Eat?

A coral polyp consists primarily of tentacles, a mouth and a gut (think upside down jellyfish). Many corals are passive feeders on plankton. Most corals also get nutrition from microscopic algae (zooxanthellae) living within their tissue. Coral polyps are generally nocturnal feeders and are provided sugars made by their photosynthetic zooxanthellae during the day.
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Where Does The Framework Of A Coral Reef Come From?

Corals extract calcium and carbonate from seawater to build an inner skeleton that is external to the coral. This external skeleton lies underneath a thin layer of tissue. Over the years millions of coral polyps in colonies create the framework of the coral reef. Coral reefs grow very slowly. It may take up to a hundred years for a coral reef to grow one meter (around three feet).

What Is The Difference Between Hard And Soft Corals?

Hard corals, also called reef-building corals, produce a rock-like skeleton made of the same material as classroom chalk (calcium carbonate). These skeletons and the various shapes of different colonies form the familiar structure of the reef. Hard corals rely on symbiotic algae (zooxanthellae) living within their tissues for nutrition and energy to build their skeleton. They must therefore live in shallow clear water to allow sunlight to reach the algae. Soft corals look like colorful plants or graceful trees and are not reef-building since they do not produce the hard calcified skeleton of many reef-building corals. However, soft corals do produce smaller amounts of calcium carbonate that help them keep their shape. Soft corals can be distinguished from hard corals by the fact that soft coral polyps always have eight tentacles, while hard coral polyps have multiples of six tentacles.

What Is Symbiosis?

Symbiosis is defined as the close association between two or more interacting organisms, usually of different species. The relationship is usually classified as belonging to one of three types: mutualism (benefiting both partners), parasitism (one partner, the parasite, benefits, at the expense of the host), or commensalism (one partner benefits while the other is unaffected). Changes in the physical environment such as the amount of sunlight or salinity, or the temperature, and in the biological community, such as the presence or absence of other organisms and how they interact with the symbiotic pair, may change the nature of the symbiotic relationship from one type to another. Like organisms, symbiotic relationships are responsive to the environment and can change over time.

What Is The Largest Coral Reef In The World?

As the name implies, the Great Barrier Reef, located off Australia’s East Coast is the largest coral reef in the world. This enormous reef is over 2023 kilometers (1257 miles) long and covers more than 300,000 square kilometers (about 186,000 miles). Home to more than 1500 species of fish, dolphins, whales and sea turtles, the Great Barrier Reef is actually a collection of more than 3000 smaller reefs. The second largest reef lies off the coast of Belize, in Central America.
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What Are The Main Types Of Coral Reefs?

Reefs are generally classified into the following three types:

Fringing reefs, the most common type of reef, form along a coastline. They grow on the continental shelf in shallow water.
  ·Barrier reefs grow parallel to shorelines but are farther from shore and are usually separated from the land by a deep lagoon. They are so called because they form a barrier between the lagoon and the seas, protecting the coastline.
  Coral Atolls are rings of coral reef growing on top of old sunken volcanoes in the ocean. They begin as fringing reefs surrounding a volcanic island; then, as the volcano sinks, the reef continues to grow, and eventually only the reef remains. There are over 300 atolls in the South Pacific. Atolls contain islands.

Do Any Animals Eat Corals?

One of the most important predators of corals is the Pacific Ocean’s Crown of Thorns Sea Star. It is estimated that a single Crown of Thorns Sea Star can eat from 2 to 6 square meters (6 to 20 square feet) of corals per year. Many fish species such as parrotfish, butterfly fish and tangs also include corals as part of their diet. Attentive divers and snorkelers hear the crunch of hungry parrotfish as they chew up their delectable meal that includes the skeleton. Other coral predators include some types of marine snails and marine slugs, known as nudibranchs. Interestingly, these coral predators digest the animal tissue and release the symbiotic algae (zooxanthellae) in their feces. The nudibranchs may also keep the nematocysts (stinging structures) and symbiotic algae for their own nutritional use.

Why Are Coral Reefs Important To Humans?

Coral reefs are among the most biologically diverse ecosystems on earth. Second only to tropical rain forests in the number of species they harbor, they are sometimes called the “rainforests of the sea”. Although coral reefs only occupy about 0.07 percent of the ocean floor (an area roughly the size of Texas), they are home to as many as one quarter of the world’s marine species. Coral reefs offer important income sources for their human neighbors through tourism and fishing, which provide both subsistence and trade. Recently, scientists have begun to discover that coral communities may contain valuable medicines that may one day lead to treatments for cancer and HIV. For coastal communities, coral reefs also play an important role in protecting their coastlines from storms.

Why Are Coral Reefs In Danger?

Coral reefs are among the most beautiful ecosystems in the world but are also among the most susceptible to human impacts and are damaged or destroyed with alarming ease. Practices such as over-fishing, the use of dynamite or poison to capture fish and dropping boat anchors on corals have produced enormous damage. Even an accidental touch from divers and snorkelers can significantly damage the delicate coral polyps. Pollution, silting from land-based construction, and fertilizer runoff have led to damage to coral reefs worldwide by blocking the sunlight corals require for photosynthesis by their symbiotic algae. Rising sea temperatures from global warming can also destroy corals by ending the symbiotic relationship with zooxanthellae. Hurricanes and earthquakes, which can also lead to significant damage to the reefs, are nonetheless generally viewed as a natural cycle of the ecosystem. However, when a coral reef has been damaged from human effects, it may have a more difficult time recovering from natural disasters such as hurricanes and earthquakes.
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