Almost all corals are colonial organisms. This means that they are composed of hundreds to hundreds of thousands of individual animals, called polyps. Each polyp has a stomach that opens at only one end. This opening, called the mouth, is surrounded by a circle of tentacles. The polyp uses these tentacles for defense, to capture small animals for food, and to clear away debris. Food enters the stomach through the mouth. After the food is consumed, waste products are expelled through the same opening.


Bangladeshi coral is the wealth of our country. “Coral” is a foreign word whose meaning is [Probal]. Coral [Probal] is a type of animal. The island of Saint Martin in Bangladesh called the coral [Probal] island. When coral [Probal] is mention, most people first think about clean, Tropical Ocean and fish land. Indeed, rocky, shallow-water corals-such as coral reefs-have only one type of coral. There is also soft coral in dark cold water and coral in deep water.

Corals are members of the phylum Cnidaria, a diverse group that includes jellyfish, hydroids, and sea anemones. Cnidarians have a simple body plan, exhibit radial symmetry, and possess specialized harpoon-like stinging cells called cnidocytes that can be fired to aid in attachment, prey capture or defense.

Corals are colonial organisms made up of individual polyps, each 1–3 mm in diameter, that are connected to one another via a thin layer of tissue. The connection between polyps allows for the sharing of nutrients. Beneath the soft bodies of scleractinian, or stony corals, polyps secrete a calcium carbonate skeleton, and it is this skeleton that becomes the foundation of coral reef ecosystems. Coral colonies can be either dioeciously or hermaphroditic and can reproduce asexually through fragmentation and reattachment. While reproductive strategies vary with the diversity of coral species, synchronous spawning events can cloud the water column with gametes and larvae.

While all scleractinian corals deposit calcium carbonate skeletons, not all stony corals grow large enough to build reef structures. In the tropics, hermatypic, or reef building corals, are able to grow and secrete their calcium carbonate skeleton with the aid of zooxanthellae, a group of single-celled dinoflagellates that live in the tissue of corals (Figure 4). Zooxanthellae are plantlike organisms that photosynthesize and exchange food and nutrients with their host coral. In the warm oligotrophic waters where corals thrive, the nutrition provided by zooxanthellae supplies the needed energy for corals to secrete layers of calcium carbonate. Even with the nutrition provided by zooxanthallae, the process of building a reef is slow. Branching species grow 10–20 mm per year while massive species grow 1 mm per year or less.

i] Is Coral an animal or a plant?

Yes, coral is an animal. In addition, unlike plants, corals do not make their own food. Corals are in fact animals. The branch or mound that we often call “a coral” is actually made up of thousands of tiny animals called polyps. A coral polyp is an invertebrate that can be no bigger than a pinhead to up to a foot in diameter.

ii] What is coral in color?

Coral (color) Coral is a reddish or pinkish shade of orange. The color is named after the sea animal also called corals. The first written use of coral as a color name in English was in 1513.


Coral reefs are large underwater structures composed of the skeletons of coral, which are marine invertebrate animals. Each individual coral is referred to as a polyp. New coral polyps live on the calcium carbonate exoskeletons of their ancestors, adding their own exoskeleton to the existing coral structure. The coral species that build coral reefs are known as hermatypic or “hard” corals because they extract calcium carbonate from seawater to create a hard, durable exoskeleton that protects their soft, sac-like bodies.

i] Functions of Coral Reefs:

Coral reefs are important for many different reasons aside from supposedly containing the most diverse ecosystems on the planet. They: protect coastlines from the damaging effects of wave action and tropical storms. Provide habitats and shelter for many marine organisms.

Coral reefs are part of a larger ecosystem that also includes mangroves and sea grass beds. Mangroves are salt tolerant trees with submerged roots that provide nursery and breeding grounds for marine life, that then migrate to the reef. Mangroves also trap and produce nutrients for food, stabilize the shoreline, protect the coastal zone from storms, and help filter land based pollutants from runoff. Sea grasses are flowering marine plants that are a key primary producer in the food web. They provide food and habitat for turtles, seahorses, manatees, fish and foraging sea life such as urchins and sea cucumbers, and are also a nursery for many juvenile species of sea animals. Sea grass beds are like fields that sit in shallow waters off the beach, filtering sediments out of the water, releasing oxygen and stabilizing the bottom.

ii] What is a coral reef used for?

Coral ecosystems are a source of food for millions; protect coastlines from storms and erosion; provide habitat, spawning and nursery grounds for economically important fish species; provide jobs and income to local economies from fishing, recreation, and tourism; are a source of new medicines, and are hotspots of. [HOTSPOTS: Such were the extremes of temperature that hot spots in the building were still smoking more than 24 hours after the fire broke out.]

iii] How do corals eat?

While most of a corals diet is obtained from zooxanthellae, they can also ‘fish’ for food too. During feeding a coral polyp will extend its tentacles out from its body and wave them in the water current where they encounter small fish, plankton or other food particles. The surface of each tentacle has thousands of stinging cells called endoblasts, and when small prey floats or swims past, the tentacles fire these stinging cells, stunning or killing the prey before passing it to the mouth.

iv] What coral reefs do for us?

Coral reefs provide a buffer, protecting our coasts from waves, storms, and floods. Corals form barriers to protect the shoreline from waves and storms. The coral reef structure buffers shorelines against waves, storms, and floods, helping to prevent loss of life, property damage, and erosion.

v] Why is the coral reef so bright and colorful?

The colors found in colorful corals are mostly due to three things – photosynthetic pigments, fluorescent proteins and non-fluorescent chromo proteins. Colorful corals contain symbiotic algae, or zooxanthellae, which are brownish or green because of the photosynthetic pigment called “chlorophyll”.

vi] What is the difference between reef and coral?

The actual coral animal or “polyp” is soft bodied, with tentacles like a sea anemone. The main difference is that corals secrete an external calcium carbonate skeleton and sea anemones do not. This hard skeleton forms the framework of coral reefs. Corals feed on zooplankton with the use of their tentacles.

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