MYSTERIOUS
WORLD OF CORAL REEFS

Coral Reefs in Andaman & Nicobar Islands

coral reefsCorals are tiny organisms belonging to group Anthozoa of phylum Cnidaria. These animals are capable of secreting a massive calcarious skeleton and collectively deposit calcium carbonate to build ornate and sometimes large colonies. Concerted growth of a variety of corals in a localised habitat gives rise to a coral reef, a complex system which consists of many animals, including corals and plants. The combination of shapes and colours as well as the variety of corals and other animals in a reef make it a fascinating and unique marine ecosystem.

Types of Reef FormationAndaman and Nicobar Islands are known for their natural Beauty, sandy beaches and rich marine biodiversity. Most of the islands are surrounded by fringing reefs on their eastern side and barrier reefs on their western side. The area covered by the reefs is about 2000 sq.km. i.e., 6 percent of the islands. They harbour a rich population of corals, molluscs, fishes etc, and most of them have luxurient mangrove vegetation closely associated with them.

REEF ZONATION

Frinzing ReefFringing reefs have distinct zones-reef flat, reef crest and reef slope. The reef flat extends out towards the sea and has a gentle gradient so that it appears almost level. At the seaward edge, it drops down suddenly to form reef slope. The narrow region just between the Profile of a Fringing Reef to reef flat and the reef slope is called reef edge or reef crest. The reef flat often gets exposed during low tide but reef slope remains underwater at all times. Corals found on reef flats and reef crests are mostly boulder-shaped while those on reef slopes display a variety of growth forms.

CORAL POLYP

coral polypMost Corals consist of many small polyps living together in a large group or a colony. A single polyp has a tube-shaped body with, a mouth surrounded by tentacles which help in feeding by capturing prey. During the day time polyps are withdrawn into their skeletons and in night, the polyps protrude out for feeding.

Hermatypic and Ahermatypic corals

Majority of hard corals harbour an algae called zooxanthallae whose pigments give the coral tissues an extensive range of colours. Such corals are called hermatypic corals and are mostly found in the upper levels of the reef slopes. They provide shelter to the zooxanthallae which in turn helps in the process of coral calcification and accelerates coral growth. coral diversityThe ahermatypic corals do not contain zooxanthallae and are usually found in the deeper parts of the reef slope. They have a slower rate of growth and do not usually form large colonies.

CORAL DIVERSITY - Andaman and Nicobar Islands are the richest of the Indian region in coral diversity with as many as 179 species belonging to 61 genera. The common genera contributing to the reef formation are Acropora, Montipora, Pocillopora, Porites, Goniopora, Favia, Fungia, Millcpora, Heliopora etc., A notable feature of these islands is the abundance of non- Soft coral (Sarcophyton sp.) scleractinian (soft) corals at certain localities. Some important soft coral species are Sarcophyton sp., Lobophytum sp. and Sinularia sp.

Table Coral is Aeropora sp. which forms flat tables and steps.

Boulder shaped Corals are common corals found on reef flats. Some important boulder corals are

Pore Coral (Porites sp.) has very small polyps and can grow into large colonies on reef edge and upper slope.

Larger star coral (Favites abdita)Larger star coral (Favites abdita) looks like an irregular shaped colony with adjacent large polyps sharing common walls.

 

Lesser star coral (Goniastrea retiformis) has small polygonal polyps.

 

Knob Coral (Favia speciosa)Knob Coral (Favia speciosa) has distinct rounded polyps with its own distinct low walls.

 

 

Valley coral (Platygyra sp.)

 

Valley coral (Platygyra sp.) has individual polyps merging to share common wavy elongated walls with the mouth situated in a single row within the valleys.

 

 

 

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