Question

What are corals? Explain the different types of corals.

Answer 1

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Corals - plants or animals?

Corals belong to the animal kingdom, and are members of the same group of animals as jellyfish and sea anemones (Phylum: Cnidaria). 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. The tiny coral polyps occupy little cups or corallites in the massive skeleton. Corals can be colonial or solitary and there are several hundred species, some are large and branching and grow rapidly at a rate of up to 10cm per year, while others are mound shaped, growing slowly at only 1cm per year.


The second largest Brain Coral in the world, at Tobago.

Reef building corals live in symbiotic association with Zooxanthellae, single celled algae, which live in the tissue of the corals. The zooxanthellae produce the oxygen, that the corals need to survive, by photosynthesis; in return the algae are protected from grazing species and can access the nutrients that the coral excretes - a mutually beneficial association. Corals feed on zooplankton with the use of their tentacles. During daylight they mostly remain within their protective skeleton to avoid predation, but at night the tentacles are extended to allow them to feed. Coral colonies grow by having the polyps bud off new polyps asexually. New colonies are established by the fragmentation of skeletal pieces or through the settling of planktonic coral lava on a hard substrate. The lava are the result of sexual reproduction.

What do corals need to grow?

There are six major factors that limit coral reef development; water temperature and salinity, depth, light, sedimentation and emergence into air.

Coral reefs are only found between about 30° north and south of the equator, where the water temperature is at least 20°C, and optimal reef development occurs in waters where the mean annual temperatures are about 23-25°C.

Corals are intolerant of salinities that deviate significantly from that of seawater and gaps will occur in reefs where, for example, freshwater from a river enters the sea....Types of Coral Reef Formations. Scientists generally divide coral reefs into four classes: fringing reefs, barrier reefs, atolls, and patch reefs. Fringing reefs grow near the coastline around islands and continents. They are separated from the shore by narrow, shallow lagoons.....



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Answer 2

Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically live in compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.