Coral Reefs: Definition, Types and Distribution | Skeleton

In this article we will discuss about Coral Reefs:- 1. Definition of Coral Reef 2. Biome of Coral Reef 3. Reef Building Corals and Other Organisms 4. Conditions for Formation 5. Fossil Corals and Reefs of the Geologic Past 6. Types 7. Theories regarding Formation 8. Distribution 9. Role of Symbionts 10. Genera of Reef Building Corals in India 11. Conservation 12. Importance.

Contents:

1. Definition of Coral Reef
2. Biome of Coral Reef
3. Reef Building Corals and Other Organisms
4. Conditions for Formation of Coral Reef
5. Fossil Corals and Reefs of the Geologic Past
6. Types of Coral Reef
7. Theories regarding Formation of Coral Reef
8. Distribution of Coral Reef
9. Role of Symbionts of Coral Reef
10. Genera of Reef Building Corals in India
11. Conservation of Coral Reef
12. Importance of Coral Reef

1. Definition of Coral Reef:

Coral reef is a ridge or mound-like biogenic structure in tropical seas composed of largely calcium carbonate and built almost exclusively by reef organisms.

2. Biome of Coral Reef:

Biome is the recognisable subdivision of the terrestrial or aquatic ecosystems, includ­ing the total assemblage of plants and animal life and their interactions within the life layer. So coral reef biome includes the reef-building corals and other organisms as well as their ecological interactions within coral reef biome.

3. Reef Building Corals and Other Organisms:

(A) Madreporarian (stony) corals:

(i) Imperforate corals, e.g., Astraea, Flabellum, Favia, etc.

(ii) Perforate corals, e.g., Porites, Madrepora, Montipora, Acropora, etc.

(B) Other corals:

Milliporans and sometimes Tubipora and Heliopora; the much calcified alcyonarians like Fungia, etc. and the gorgonarians are also recorded from the beds of Carribean— West Indies region.

(C) Non-coral animals:

Eighty mollusc shells and skeleton of Foraminifera (shelled protozoa), sponges, sea anemones, flatworms, shrimps, crabs, lob­sters, octopuses, squids, some snails, bivalves, starfishes, sea urchins, sea cucumbers, tunicates, turtles, sea snakes and many reef fishes that include sharks, eels and rays form an important constituent of the coral reefs.

Pillai (1986) has recorded different kinds of fishes, turtles, dugongs as coral fauna in the Gulf of Mannar. He has recorded the different kinds of fishes, such as butterfly fish (Chaetodon sp.), parrot fish (Scarus spp.), squirrel fish (Holocentrus spp.), snapper (Lutjanus spp.) and the eels Gymnothorax undulatus and Gymnothorax punctatus, etc.

The green turtle (chelone mydas), Olive turtle (Lepidochelys olivacea), sea snakes, dugongs (Dugong dugon) and algal sea grasses are present in this area. Turtles and dugongs are dependent on sea grasses.

These inhab­itants when exposed to low tide are sub­jected to predation by birds, such as gulls and golden plover, etc. A few of the above mentioned species feed directly on corals, and others graze on algae and participate in food webs.

(D) Plants:

Calcareous coralline sea weeds are Lithophyllum, Lithothamnion and Melobasia of the red algae, Helimedia of green algae re­corded in the coral reef areas.

In the Gulf of Mannar and around the Krusadai island area the following algae have been recorded, such as Ulva recticulata, Helimedia apuntia, H. tuna, Caulerpa racemosa of green algae; Sargassum spp. Turbinaria spp. of brown algae and Gelidiella acerosa, Gracillaria edulis, G. crassa and Polysiphonia spp. of red algae. The sea grasses are Halophilia ovalis, H. decipiens, Thalassia hemprichii, Cymodocea serrulata, Enhalus acuroides, etc.

4. Conditions for Coral Reef Formation:

The reef-building (hermatypic) corals re­quire certain requisites for the formation of coral reefs.

These are:

1. Temperature:

The water must be warm and the coral reefs require a temperature between 20°C to 30°C for their growth and best developed is recorded within the range of 25°C—29°C, but do not develop where tem­peratures fall below 18°C. So the major coral reefs are confined to the tropical and sub­tropical waters between 30° North and 30° South latitudes.

Generally, the corals do not thrive above the temperature of 33°C but few reefs in the Arabian sea regularly encounter above the temperatures of 33°C in summer and below 18°C in winter.

2. Depth of the sea:

The depth of the seas is an important factor for the growth of coral reefs. The coral reefs grow in relatively shallow water and the depth is related to the entry of sunlight for photosynthesis.

Russel and Yonge (1963) reported that corals could grow outwards as far as 30 fathom (180 feet) and below this depth line light is insufficient for the proper nutrition of their associated plants. It has been reported that the reef-building corals grow ranging to depths of 60 m.

3. Sunlight:

Sunlight is also very much essential and required for the photosynthesis of symbiotic zooxanthellae, (Symbiodinium microadriaticum) present in the endoderm of the reef-building cnidarians. They are not found in non-reef building corals such as Dendrophyllia.

They are also found in the Millipora, Tubipora and Heliopora. They also help to secret skeletons (limestone or CaCO₃) and contribute to the formation of reef structure. It has been shown experimentally that the reefs fail to grow in shady places and may die if kept in total darkness.

4. Clear Water:

The water must be clear which permits the penetration of sufficient sunlight, related to the photosynthesis of zooxanthellae (a symbiotic alga), and also other macro algae which are present in the coral reefs. One species Porites limosa lives in muddy condi­tions.

5. Suspended particles and sedimentation:

The continental sediments, such as silts, sewage and industrial disposals which in­crease the turbidity of water, reduces light, thereby inhibiting the photosynthesis by the symbiotic brown algae. Corals can grow only in shallow, clear waters, free from suspended particles. Silt can block the mouth of corals and prevent the feeding.

The major rivers which carry the silt and disposals prevent the process of photosynthesis. So corals are not found in the deltaic areas. The corals are not found also in the eastern part of India due to presence of several large rivers, such as the Ganges, Subarnarekha and Mahanadi, etc.

Water turbidity inhibits active coral growth along the east coast of south America and cold water currents perform the similar task on the west coast of Africa.

6. Salinity:

The reef can grow with a specific salinity. They can tolerate salinities between 30 and 40 ppt. But one species Madrepora cribripora inhabits nearly freshwater.

7. Nutrient:

They can thrive in areas which are poor in nutrients because a large amount of nutri­ents such as planktons and mega algae, smother the corals blocking out the light.

8. Precipitation of Calcium:

Precipitation of calcium from sea water is necessary to form the skeleton of coral polyp. This precipitation occurs when water tem­perature and salinity are high and CO₂ con­centration is low.

9. Waves and Currents:

The coral reefs can thrive in reduced waves but the absence of waves and currents helps to accumulate the silt in muddy patches that can suffocate the coral.

Remark:

It is reported that coral reefs or reef-building corals may grow upwards at the rate of 1 foot (30 cm) in about 12 years under op­timum conditions, viz., in clear, shallow tropical seas where the temperature remains about 20°C throughout the year.

5. Fossil Corals and Reefs of the Geologic Past:

More than 6,000 fossil coral species have been recorded in different oceans and are included under the existing order Madreporaria and to the extinct orders Rugosa and Tabulata. The tabulate corals and rugose corals formed reefs during the Palaeozoic era but they were replaced by Madreporarian corals during the Coenozoic era.

The reef building species did not become prominent until the Mesozoic and a great diversity was probably attained during the Cretaceous period. The tabulate corals are characterised by the well-developed tabulae, ridges or spines and also tube-like corallites.

The group is represented by Syringopora and Heliolites. The reef building corals had a much wider geographical distribution as compared with the present day distribution. Their fossils have recorded in temperate and even polar regions.

6. Types of Coral Reefs:

On the basis of structure and the under­lying substratum Charles Darwin (1831) classified 3 types of coral reefs.

They are as follows:

(1) Fringing reef or Shore reef,

(2) Barrier reef, and

(3) Atoll.

1. Fringing reef or Shore reef:

(i) The fringing reef or shore reef (Fig. 12.40A, B) is extended from the sea shore to the seaward directly and surrounds the shores of tropi­cal islands or may be a stretch of continental coast line.

(ii) It extends from the coast a few meters to 400 meters as bench or platform and takes the contour of the shore.

(iii) The fringing reef consists of mainly 3 regions, namely (i) reef front or fore reef slope, (ii) reef crest, (iii) and the back reef, sometimes referred to as the reef lagoon or reef flat area.

(iv) The seaward side of the fringing reef has a reef edge, called reef front or fore reef slope where the most active coral growth occurs.

(v) The coral growing areas represent a narrow belt-like structure and is about 20 to 40 m wide and subject to continuous surf and below to this zone is usually a lot of dead corals, rubble and sand.

(vi) The reef front varies from gentle to steep and in some reefs the lower part of the reef front is nearly ver­tical and is called drop off.

(vii) The reef front is often interrupted by terraces or shelves. Sand and sediment will collect in terraces.

(viii) At the upper part of the reef front there is an emergent portion, called reef crest. The seaward side of the reef crest takes the brunt of the wave action. The reefs can reduce the wave action up to 97% and the rest of the waves break across the reef crest.

(ix) Between the reef crest and the shore there lies a more or less flat area often eroded and uncovered at low tide, called back reef area or reef flat area.

(x) The back reef area or reef flat area is shallow and is usually 50 to 100 metres or more broad (It may be a few kilometer).

(xi) Sediment, rubble, coral masses and reef fragments torn off by the break­ers and are dumped behind the crest and widen the back reef flat. This zone is sometimes called boul­der zone.

(xii) The reef flat area remains sub­merged at high tide but at low tide the water seems to run rapidly exposing more or less the whole surface.

(xiii) The zone between the boulder zone and shore is called inner flat which contains a shallow narrow chan­nel, sometimes deep enough for the passage of local boats but not ships (Fig. 12.40).

(xiv) The reef flat ends at the shore in fringing reefs and descends into the lagoon to atolls and barrier reefs.

(xv) It is the simplest and relatively young type of all reefs and is com­mon in the tropical seas. It is seen in the Gulf of Mannar, Palk Bay, and in the western part of Andaman and Nicobar islands. In the west coast of India fringing reefs are seen in the Malvan coast and in the Gulf of Kachchh including Pirotan island.

Other areas of fringing reef may be mentioned in the Barba­dos, Sri Lanka, east African coasts, Indonesia, South-eastern coast of Curacao, Islands of Tarutao group (Thailand) and South Pacific Ha­waiian islands.

2. Barrier reef:

(i) The barrier reef resembles the fring­ing reef but grows in deep water than the fringing reef (Fig. 12.41A,B).

(ii) It develops around islands or along the edges of continental shelves and is separated by a wide a relatively deep channel, called lagoon, which is 20 to 100 metres deep and 1/2 to 10 miles wide through which ships can easily navigate.

(iii) The largest barrier reefs which lie on the edge of continental shelves and over 160 km distant from the mainland (e.g., Great Barrier Reef of Australia) are sometimes referred to as shelf barrier reefs to differen­tiate them from the much smaller barrier reefs surrounding the islands.

(iv) Like the fringing reefs the barrier reefs are divided into (i) reef front area (ii) Reef crest and (iii) back- reef area or flat reef area contain­ing lagoon.

(v) The place of inner reef of the back reef area is taken by a lagoon.

(vi) Towards the lagoon side of the barrier reef there grow more fragile corals than the outer slopes which descend to great depths of hun­dreds and thousands of fathoms, and tolerate more violent waves.

(vii) The lagoon flat is covered by a thin layer of sand and has a luxuriant coral growth. If there is a good circulation of water there may be the growth of patch reefs.

(viii) A number of small channels which cut across the barrier reefs and con­nect the lagoon with the open sea. Through these channels fresh and colder waters pass into the lagoons.

The typical example of the barrier reef is the Great Barrier Reef of Australia which is the largest reef in the world, stretching over 2600 km, off Queensland, Australia. Another relatively short barrier reefs are New Cal­edonia Barrier Reef (1000 km), the Bahama Barrier Reef between Andros and Nassau.

3. Atoll:

(i) The atoll (Fig. 12.42A, B) is more or less circular or horse-shoe shaped coral reef, enclosing a central area of water, called the lagoon.

(ii) The lagoon varies from a few hun­dred meters to 90 kilometres in diameter and 20 to 90 metres in depth.

(iii) Atoll generally arises first as a fring­ing reef around volcanic islands. As the volcanic island subsides because of the seafloor sinking or seafloor rising, the atoll rests on the summit of the submerged volca­noes.

(iv) The lagoon usually contains inner islands and reefs.

(v) Atoll is not connected with the mainland and is separated by hun­dreds or thousands of kilometres from the land.

(vi) The atoll reef may be complete or broken by a number of channels of which a few are navigable in be­tween lagoon and outer seas.

(vii) There is a seaward slope to the outer-side of the atoll reef and inner side of the reef descends as the lagoon slope (Fig. 12.42).

(viii) The sediment of the lagoon floor consists coral sand and mud.

(ix) Atoll is also called coral island and the term ‘atoll’ is derived from the language of Maldives where a dis­trict is called atolu.

More than 300 atolls are present in the Indo-Pacific region and the largest atoll of the world is Kwajalein in the Marshall is­land of the Pacific Ocean that surrounds a lagoon over 97 km. Lakshadweep islands are an example of Indian atoll.

In addition to the above mentioned prin­cipal types, three or four other minor types may be discussed. These are:

(a) Table reefs (Platform reefs):

These are small open oceanic reefs but without central islands or a lagoon.

(b) Patch reefs:

These are small circular or irregular reefs which develop from the floor of lagoons behind barrier reefs or within atolls. They possess rather typical lagoon features and are very often numerous.

(c) Apron reef:

A shore reef resembling a fringing reef but more sloped from the shore area.

(d) Bank reef:

A linear or semi-circular in outline larger than a patch reef.

7. Theories regarding Coral Reef Formation:

The reef-building corals obey certain conditions to form coral reefs. They do not grow well below 60 metres, they require optimum temperature and light. Many theo­ries have been put forward to explain the formation of coral reefs.

Some such theories are discussed below:

1. Darwin-Dana Subsidence theory:

This theory has its origin from the obser­vations of Darwin during his remarkable voyage in the ship, H.M.S. Beagle as a natu­ralist between 1831 and 1836. The theory states that from fringing reefs arise other types of coral reefs. Fringing reefs are formed on shores which are inclined downward. Sometimes the shore between the develop­ing fringing reef and the land mass sinks.

The fringing reef thus turns into a barrier reef. The barrier reef and the main land mass always have sea water between them. In case the main land mass is an island and it itself subsides completely under water, the reef turns into an atoll (Fig. 12.43A).

Remark:

This theory was forwarded first by Charles Darwin in 1842 con­cerning the origin of barrier reefs and atolls. Regarding the concept there were some doubts. First three types of reefs are found in the same area which does not favour Darwin’s view.

Second a general sinking of a great belt of land between the tropics over a long period seems to be unbeliev­able. This theory was supported by an American geologist, James Dwight Dana in 1890. He changed some portion’s of Darwin’s view and stated that the sinking of each land mass might have taken place independently.

Most modern zo­ologists still support Darwin’s view. Darwin’s reef evolution theory was finally verified in 1950s for Indo-Pacific reefs after analy­sis of the results of deep drilling at Bikini and Eniwetok atolls.

2. Semper-Murray Solution theory:

After exploring the conditions of life in the sea, Sir John Murray of Harvard Univer­sity advanced the view in 1880 that corals grow on the highest peaks of the ocean bottom. The deposition of sediments brings them to an optimum level. The barrier reefs and atolls are produced by better growth of the corals in the edges of the coral deposition and by the solution of its inner part (Fig. 12.43C).

Remark:

This theory was completely dis­carded by Hyman (1940) but oth­ers like Russell and Yonge (1936), Barrington (1979) and many oth­ers favour this theory in many points such as (i) the theory does not want the general subsidence of the land over the tropics and (ii) the reefs were founded on the tops of submarine volcanoes and these reefs raised to suitable lev­els by deposition of sediments.

3. Submerged Bank theory:

This concept is supported by many inves­tigators of the present time. According to this theory the coral reefs are formed on flat surfaces which at first remain in lesser depths.

Such surfaces with growing reefs later on submerge slowly and go down to greater depths. This theory denies the transition of one common type of reef into different types. It advocates an independent origin of different types of reefs. Further, regar­ding the shape of the atoll, it lays impor­tance on the winds and water currents (Fig. 12.43B).

4. Daly Glacial-control theory:

This theory advocates by Prof. Daly of Harvard University in 1915 that during the last glacial period, formation of ice caps lowered the level of water of the ocean. At that time extreme cold temperature prevailed. Subsequently the ice melted and the tem­perature rose.

The corals began to grow upon the flat platform of the ocean bottom and kept pace with the rising level of the ocean. The support to the Daly Glacial- control theory was given by calculating that almost all the existing coral reefs had been formed since the Ice-age (Fig. 12.43D).

As regards the formation of atolls, Huxley and Wells have put forward the view that atolls might have come into existence in other ways. From the geological point of view, submarine eruptions are quite frequent in the ocean bottom.

By such catastrophe, volcanic cones were raised above the sea level and the erosive action of the sea waves became so severe that their tops were even­tually smoothed off to provide an ideal plat­form for the future atoll.

Discussion:

Despite great controversies regarding the origin of coral reefs, the most obvious con­clusion that may be drawn is that the coral reefs of the present day grew on submerged land.

This contention is attested by evidences from different angles. The rate of coral growth is of much importance for the explanation of the theories on this line. But the observations showed that the growth of coral is extremely variable.

8. Distribution of Coral Reefs:

(A) Geographic:

Corals grow in shallow water and mainly ranges to depths 45 to 60 m and grow best at temperatures between 25°C and 29°C. The minimum temperature they can tolerate in about 18°C.

Consequently they are scattered throughout the tropical and subtropical Western Atlantic and Indo-Pacific oceans extending between 30° North and 30° South from the equator where the temperature remains above 20°C throughout the year.

Existing reefs are restricted to the following regions:

(i) In the Caribbean Sea, the coasts of Limon (Costa Rica), the West Indies, the Bahamas, Bermuda, Belize (off Guetmala), Grenada, Mexico and Venezuela are inhabited by 35 reef building corals.

(ii) The tropical Indo-Pacific region in­cludes Sudanese Red sea coast, East Coast of Africa including Madagas­car, Seychelles, Maldives, Cocos, In­dian coast including Lakshadweep and Andaman and Nicobar Islands, Sri Lanka, Myanmar, Thailand and Malayan Archipelago, etc. in the In­dian Ocean side.

In West Pacific Ocean, coral reefs are found in the innumerable Pacific Islands, such as reefs in the Gulf of Siam, reefs of Borneo, Philippines, New Guinea, Papua, New Ireland, New Britain, Okinawa, Solomons, New Caledonia, Fiji, Samoa, Cook Island, Tonga, Soci­ety Islands, Tuamotu Archipelago and Hawaii Islands (Fig. 12.44).

The Great Barrier reef of North East Australia is the largest barrier reef of the world and has recorded six of the world’s seven species of marine turtle, over 1,500 species of fish and almost 5,000 species of mollusc. It comprises over 2900 separate reefs and 900 islands stretching over 2600 km (1612 miles) and covering over 348,000 sq km.

(B) Bathymetric:

The hermatypic corals show a limited vertical distribution also, because the tem­perature of sea water declines with depth. Further, the coral polyps harbour symbiotic zooxanthellae in their gastrodermis which help in the deposition of coral skeleton.

The total surface areas of the coral reefs occupy less than one tenth of one percent of the world ocean.

9. Role of Symbionts in Coral Reefs:

The coral polyps harbour symbiotic brown algae, zooxanthellae, Symbiodinium microadriaticum which reside in the endodermal tissue of polyps. Yonge and his colleagues, during the Great Barrier Reef Expedition in 1928-29, demonstrated the ex­istence of a symbiotic relation between the corals and zooxanthellae.

From their studies it was evident that the symbiotic algae pro­duce sugar and oxygen through photosyn­thesis, provide nutrients for their hosts and gain protection, carbon dioxide and materi­als for protein synthesis like nitrogen and phosphates from the hermatypic corals. Ac­cording to Goreau (1966), the algae utilise a variety of host excretory products including NH₃, uric acids and phosphates, aminoacids, etc.

The extent of the Indian coast line is over 8000 km and the total area of coral reefs is about 2375 sq km.

The types of coral reefs with their sites are given below (Fig. 12.44).

(i) Fringing reefs:

Gulf of Kachchh (Gulf of Kutch) including Pirotan Island; Palk Bay and Pamban pass and Gulf of Mannar including Krusadai Island, Andaman and Nicobar Islands.

(ii) Barrier reefs:

On the West Coast of Andaman and Nicobar Islands. The barrier reef in the Gulf of Mannar is about 140 km long between Pamban and Tuticorin.

(iii) Atolls:

Lakshadweep Island in the Arabian Sea.

(iv) Table (Platform) reefs:

Along the gulf of Kachchh (Gulf of Kutch).

(v) Patch reefs:

Mainly seen at the intertidal areas along the West coast from south of Mumbai to Goa. The main sites are Angria Bank, Ratnagiri, Malvan Coasts and Redi. In the east coast the places are near Visakhapatnam port, Pondicherry, and in the Gulf of Mannar there are 1 to 2 km in length and width as much as 50 metres.

10. Genera of Reef Building Corals:

A list of some genera of reef-building corals in India:

C. S. Gopinath Pillai (1983) has recorded 71 genera including 199 species from India including gulf of Kutch (Gulf of Kachchh), Palk Bay and Gulf of Mannar, Lakshadweep, and Andaman and Nicobar Islands.

He recorded 24 genera including 31 species in the Gulf of Kachchh, 37 genera including 94 species in the Palk Bay and in the Gulf of Mannar, 59 genera with 135 species in Andaman and Nicobar Islands and 31 genera with 78 species in Lakshadweep. Venkataraman et al. (2003) have dealt a total of 208 species which include 15 families and 60 genera.

Gulf of Kachchh (Gulf of Kutch):

Siderastrea

Meandrina

Porites

Montipora

Acropora

Psammocora

Goniopora

Favia

Favites

Platygyra

Leptastrea

Goniastrea, etc.

West coast (From Mumbai to Goa):

Porites

Turbinaria

Favia

Pseudosiderastrea

Favitas

Palk Bay and Gulf of Mannar:

Poecillopora

Acropora

Astreopora

Montipora

Pavona

Goniopora

Porites

Favia

Favites

Echinopora

Dendrophyllia

Goniastrea

Platygyra

Galaxea

Tubinaria

Balanophyllia

Leptostrea

Pachyseris

Psammocora, etc.

Andaman and Nicrobar Islands:

Acropora

Poecillopora

Montipora

Fungia

Porites

Turbinaria

Astreopora

Seriatopora

Stylopora

Euphyllia

Physogyra

Siderastrea

Pavona

Pachyseries

Coeloseris

Cycloseries

Halomitra

Echinophyllia

Merulina

Hydrophora

Favites

Favia

Echinopora

Goniopora

Montastrea

Lakshadweep Islands:

Acropora

Alveopora

Osypora

Pectinia

Pachyseris

Ontophyllia

Trachyphyllia

Pterogyra

Porites

Psammocora

Helipora

Millepora

Montipora

Astreopora

Galasea

Pavona

Merulina

Turbinaria

Echinopora

Fungia

Favia

Favites

Table 12.7: Cnidaria

A list of some reef-building coral species of India:

Gulf of Kachchh:

Fam. Siderasteridae:

Siderastrea savignyana

Psammocora digitata

Fam. Poritidae:

Porites lutea

Porites compressa

Porites lichen

Goniopora stutchburyi

Goniopora planulata

Fam. Acroporidae:

Acropora humilis

Montipora venora

Montipora foliosa

Montipora explanata

Fam. Faviidae:

Favia speciosa

Favia favus

Favia pallida

Favites complinata

Favites halicora

Platygyra sinensis

Palk Bay and Gulf of Mannar:

Fam. Poeciloporidae:

Poecilopora verrucosa

Poecillopora demicoris

Fam. Acroporidae:

Acropora millipora

Acropora intermedia

Acropora digitifera

Acropora rudis

Acropora echinata

Astreopora myriophthalma

Montipora foliosa

Montipora tuberculosa

Montipora digitata

Montipora manauliensis

Fam. Agariciidae:

Pavona clavus

Pavona cactus

Fam. Poritidae:

Poritis lutea

Porites solida

Goniopora stokesi

Fam. Faviidae:

Favites helicora

Favites abdita

Favia pallida

Favia speciosa

Andaman and Nicobar Islands

Fam. Acroporidae:

Acropora humilis

Acropora nasuta

Acropora valida

Acropora aspera

Montipora acquituberculata

Fam. Fungiidae:

Fungia fungitis

Fungia scutaria

Ctenactis crassa

Fam. Faviidae:

Favia stelligera

Favia speciosa

Favitis bestae

Favitis abdita

Goniastrea ratiformis

Fam. Poritidae:

Porites lutea

Porites solida

Porites lobata

Goniopora stokesi

Goniopora planulata

Fam. Mussiadae:

Lobophyllia corymbosa

Symphyllia recta

Symphyllia radians

Fam. Dendrophyllidae:

Turbinaria peltata

Fam. Merulinidae:

Merulina ampliata

Fam. Poeciloporidae:

Poecillopora damicornis

Poecillopora verrucosa

Seriatopora hystrix

Stylophora pistillata

Lakshadweep:

Fam. Acroporidae:

Acropora digitifera

Acropora intermedia

Acropora aspera

Acropora echinata

Montipora spongiosa

Montipora digitata

Fam. Agariciidae:

Pavona varians

Pavona maldivensis

Pavona clavus

Fam. Fungiidae:

Fungia danai

Fungia fugitis

Fam. Faviidae:

Favia stelligera

Favia favus

Favites halicora

Favites complinata

11. Conservation of Coral Reefs:

The destruction of coral reefs are due to excessive siltation, industrial disposals, sa­linity changes, severe tropical storms, emer­sion at low tide, excessive exploitation for commercial purposes by different agencies, feeding activities of multi-armed starfish, Acanthaster planci, global warming, ozone depletion, earth movements and tsunamis (Seismic sea waves).

The unusual hot summer with delayed monsoon after Indian Ocean Tsunami of 2004 has added to the list of the causes of destruction of the coral reefs. The news was reported in the Telegraph, a daily newspaper in Kolkata, published in 1 November, 2010.

A team of scientists of Zoological Survey of India (ZSI) reported after a study that out of 446 species in the coral reefs in the Andamans, 120 had perished due to overheated sea water in summer, 2010.

The summer of 2010 had continued till the June and the tempera­tures of the sea water had risen above 33 degrees Celsius. The overheated sea water with delayed monsoon had played a role in the bleaching and decay of the reefs in Andaman Sea which are found up to a depth of 5-10 feet. The bleaching and decay in the reef were also noticed in the seas of Myanmar, Thailand and Indonesia after the summer of 2010.

1. Excessive siltation is responsible for the deaths of corals. The coral reefs along the Sudanese Red Sea coast with a rich variety of invertebrates and vertebrates are threatened by industrial discharges and waste disposal near Port Sudan. Every rainfall carries the fertilizer, silt, pesticides, and agrochemicals into coastal waters which are responsible for the death of reefs.

The Eastern Caribbean coral reefs are increasingly threatened by human activity. As de­velopment activity accelerates, living reefs are gradually smothered with sediment produced by dredging and shoreline construction.

2. The reefs are destroyed by a marked reduction in salinity by the influx of the large volume of freshwater, car­ried by the rivers.

3. The heavy rain associated with cy­clone is responsible for the destruction of reefs. It was reported that the de­struction of the Great Barrier Reef in Whitsunday area caused by heavy rain with a cyclone in 1918.

4. Severe tropical storms are a major cause for the mortality of corals on reefs. Moorhouse (1936) reported the devastation of corals in the Great Bar­rier Reef at Low Isles caused by a cyclone in 1934. The severe tropical storms and hurricane have caused a large scale mortality of corals on reefs of British Hondurus.

The extended shallow reef flats of Tarutao National Park in Thailand have over 50% death of corals but seaward reefs edges and reef slopes vary from 20% to 95% death. The contributing causes which have been identified are heavy rainfall, storm damage, blast damage, exposure to air, and predation by multi-armed starfish, Acanthaster planci.

5. Removal of larger corals used in white cement factories for making cement is a common practice in many underde­veloped countries including India. Quarries when collected large coral heads from reefs destroy smaller cor­als in the process. Mahadevan and Nayar (1972) estimated that 25,000 tons/year were exploited from Gulf of Kachchha, Pirotan Island, Palk Bay and Gulf of Mannar for these facto­ries. So coral extraction must be stopped for this purpose.

6. Strict enforcement of coral reefs min­ing conditions should be applied.

7. Firewood collection and goat and cat­tle grazing on the different islands will be stopped.

8. All toilets should be biological toilets to stop the sewage.

9. The coral reefs have been endangered by the trawling activities, dynamite fishermen and over enthusiastic col­lection of various reef specimens.

10. Careless tourists handle or even stand on living corals, impaling the coral animals upon their own skeletons. The collection of shells and corals for orna­mental trade contributed a great dam­age to the reefs in some places.

11. Some reefs are being dismantled piece by piece when corals are collected for souvenirs. Dynamite blasting by fish­ermen in reefs, is done for the collec­tion of various stunned fish, lobsters gastropodes, etc. Sometimes dynamite is used destroying reefs hundreds of years old for a single day’s catch. India, Kenya and other countries have banned collection and selling of cor­als, shells, etc., but selling of these ma­terials in different resorts in India is still widespread.

12. The massive destruction of corals on coral reefs in Great Barrier Reefs and at Guam, Palau and in some parts of the Tropical West Pacific region due to the feeding activities of the multiarmed starfish Acanthaster planci has been observed. But there is little information available on the rates of recolonization and reef recovery at such sites.

A lack of awareness among people and also lack in technical knowledge are the main hindrances for the conservation of coral reefs. The effective conservation of the coral reefs in the different seas may be established by securing conservation legislation of the whole area, establishing marine parks, re­serves and promoting public awareness among local people and tourists.

In India several marine National Parks or reserves (such as Marine National Park in the Gulf of Kachchha including Pitotan Island (Jamnagar, Gujarat), Malvan Marine Sanctuary, Sindhudurg, Maharastra; Marine National Park at Krusadi Island in the Gulf of Mannar, Tamil Nadu; Mahatma Gandhi Marine National Park at Wandoor, South Andaman and Jhanshi Marine National Park, Richies Ar­chipelago in the Bay of Bengal around Andaman and Nicobar have been established.

To protect the reefs various programmes may be introduced:

i. Marine conservation committee should be formed and the members of the committee should have the power of approval in any construction near the shore.

ii. With the help of audiovisual equip­ment a series of talks accompanied by slides and movie shows about the conservation of coral reef environment should be shown to secondary stu­dents, college students and university students, navy officers, police officers, sea scouts, fishermen and various clubs.

iii. The conservation message should be conveyed to a wide audience through T.V.

In St. Lucia, West Indies, a coral reef monitoring programme was estab­lished in 1983 and this carried surveys of locally important reef areas. Equally important a local constituency has been developed for reef protection, and coastal development projects are be­ing closely scrutinised for potential impact on nearby coral reefs.

iv. Education is the basis of sound con­servation, a lot of effort should be put into it.

v. To protect from the destruction of coral reefs an underwater part should be started in which a law prohibiting spearfishing and coral collecting are introduced and a regular boat patrol­ling will reduce the above mentioned cases significantly.

12. Importance of Coral Reef:

1. In spite of all controversies it cannot be denied that the coral and the coral reefs played a great and significant role in geological history. They protect the coast from the erosive actions of the sea waves.

2. The reefs provide a habitat for the thousands of marine species and use the place for hiding, feeding and re­production.

3. The reefs serve as a source of food and medicine and act as storage bank of genetic resources.