Other chapters in this dialogue: 
Coral Diversity | Coral reefs | Coral resources | Protection of corals | Main Page

66. The coral reefs must pay for being so rich, do they?

Yes, they do. But not all damages are man-made. Some are natural and at least one cause was natural in the beginning but got aggravated by human activities later.

67. What is the natural threat that has been aggravated by human activities?

Predation by the crown- This is an interesting story.  

The starfish is normally present in the reefs in very low numbers. The triton snail feeds on the young ones of the starfish and thus keeps the population of the starfish in check. But when we started harvesting triton shells in commercial quantities, there were not enough snails left to feed on the young starfish. The latter started growing in proliferation and their feeding on corals increased dramatically.  

That was how many reefs got totally devastated by the starfish outbreak.

This is an example of how unregulated human activities can aggravate natural damages, even indirectly.

68. Was there any other natural event that caused as much damage?

Yes, the unusual summer warming of the year 1998. Even in tropical seas, temperature changes follow a seasonal cycle, with increase in summer. Sometimes corals react to this increase in temperature by expelling their zooxanthellae. As a consequence the corals lose their colour and look white. This is called bleaching.

Bleaching is a common phenomenon in most coral reefs in summer but never reaches a severe degree. The bleached corals usually recover their colour once the temperature comes back to normal. The temperature increase in these instances is generally less than 1 degree and lasts for only a few days or may be a week or two.

During the1998 summer, however, a vast layer of warm surface waters spread over the whole tropical region. As a result, the temperature increased by 2 degrees higher than the seasonal maximum and persisted for several weeks. This was too much for corals. Most of them, in particular the branching corals which are more sensitive, got bleached and died, eventually leaving vast stretches of the reefs barren..

More than 40 countries reported impacts varying from moderate to severe. In India, Andaman and Nicobar reefs were the most severely affected (up to 80% death of corals) followed by Lakshadweep (40%-80%) and Gulf of Mannar (60%) reefs.

69. What other natural causes affect corals?

Exposure. Corals living in the intertidal zones get periodically exposed to atmosphere. This lasts generally 1-2 hours and all the coral species can withstand this exposure. But in regions of high tidal amplitude, as in the Gulf of Kachchh, this exposure can last several hours. If this also happens to coincide with sunny weather, then it can kill corals. Fortunately, this does not happen often.

70. Do corals also must breakdown at one time or other?

Yes, they do. A coral colony is home to many animals and plants but some of them are not that grateful! The mollusks, worms and sponges are notorious - they bore into the coral skeleton to make their homes there. In the process they weaken the skeleton and make it susceptible to mechanical breakdown by wave action.

71. So, waves also affect corals.

Yes, continuous pounding by waves on the fore reef and reef flat kills many corals there. That is why you find lots of rubble and less of live corals there. But if the wave action is very strong, as during hurricanes, corals even several meters below can also be broken to pieces or uprooted by the waves. Hurricane damages are common with Pacific reefs but rare in Indian reefs.

72. Well, these are known threats. Are there potential threats?

Yes, one such is the sea level rise. You may remember that we said entire reefs got drowned in the past because of a rise in sea level. But this happened over many centuries.

In the present century, this is happening in decades. We are burning so much of coal and oil that the carbon di-oxide concentration in the atmosphere is increasing rapidly. This causes the earth to warm up which in turn causes polar ice caps to melt. This makes the sea level to rise at a rate higher than the reef growth. If this continues then the coral reefs will be drown.

73. But I read that the sea level is not rising as much as we thought earlier, is that right?

Nobody knows for certain. It is possible that the rate of sea level rise is reduced now but it does not seem to have reversed. There are different possible scenarios, from low to high rates of rise. 

The atolls will be the most affected; even if they grow faster, they may not be able to cope up with projected sea level rise in the next century. The fringing and barrier reefs may fare better, keeping up with the sea level rise up to mid-range projection. In any case, the threat is real but its magnitude is difficult to gauge now.

74. Will this have serious fall-outs?

In the case of mainland, the protection offered to the coasts by the reefs would be lost. There will be increased erosion and land loss. In the case of islands like those of the Lakshadweep, the situation will be still worse. These low-lying islands, hardly a meter or two above sea surface now, can get drowned completely.

75. But are there man-made effects that have immediate impacts?

Yes, the most important among them is coral mining. Very often, corals are removed and used to build houses and produce lime. For most of the coastal villagers, this comes free from the sea and they have no qualms in taking away as much as possible. Unfortunately, they make no distinction between dead and live corals. 

As a result, several large patches of low-lying reefs are totally lost. This impact is most serious in the Gulf of Mannar reefs, especially near the coastal villages and towns like Mandapam and Tuticorin.

76. But these are only local impacts and people do need some coral stones, don’t they?

Well, if the removal is only moderate and restricted only to dead corals, like coral debris, then perhaps the impacts could be minimized. But most often, people do not make any distinction between dead and live corals, nor do they respect any limit for extraction. And if the extraction is on an industrial scale, then it could be catastrophic. 

Did you know that the extraction of coral sands in Gulf of Kachchh was leased out to a cement company in the eighties? Every year about a million tonnes of coralline material, including live corals, were dredged out, killing a large portion of the reefs in the process. Fortunately better sense prevailed and this lease was not renewed. But then the damage was already done the loss of coral cover was in excess of 50% at most of the reefs in the leased area.

77. But can’t we allow some corals to be collected as souvenirs? I’d like to take a coral home.

That is precisely the problem. If each one of us want a coral like that, we would then need one billion corals. Not even all the world reefs put together can satisfy this need! 

And again, we all want the beautiful branching corals. 

That means the removal is selective, affecting the biodiversity. Some fish which live only with the branching corals will also disappear and the very beauty of the reef will be lessened. What do you prefer - looking at the colourful corals in all their splendour in the reefs or their bleached skeletons in the showcases? 

Is there a choice?

78. Okay, I get your point. But don’t tell me I can’t even catch some fish to eat!

You can, as long as you use a line or a trap or a harpoon. If you resort to other methods, then it is a different story.

79. How?

Some methods used for fishing in reefs are highly destructive. 

In one such method the fishermen dive to the reef floor and release a poison. The fish in the surrounding area get narcotized and float to the surface where they are collected. What is not seen is the death of all other organisms near the site where the poison is released. 

In a similar way, some fishermen use dynamites underwater. The fish get stunned with the shock waves and float to the surface. The damage in this case is much more intensive. All corals in the vicinity of the blast are smashed to bits. In both these methods of destructive fishing, damages are not visible to the casual observer and often the impact goes unnoticed until it is too late.

80. Are such methods practiced in India?

Fortunately, no. The fish poison (generally called Rotenone) or the dynamite material is not easily available to ordinary fishermen. Some fishermen, however, use poisons extracted from locally available plants and animals.

81. But I am sure some forms of fishing practiced in India that is more destructive than productive, is it not?

Yes, it is the practice of collection of live baits and the ornamental fish. The live-bait fish are used in pole and line tuna fishing. The ornamental fish are collected for sales. Both these groups of fish usually live between the coral branches or around the coral colonies. 

The fishermen encircle large patches of corals with fine mesh cloth or net and hit on the corals to chase the fish out. In the process of collecting these fish worth a few hundred rupees, colonies of corals growing for several years are killed.

82. Are there unintentional damages associated with fishing?

Yes, the most common and the most serious one is that made by anchors.

Most of the fishermen, when they go for reef fishing, anchor their boats in the shallow parts of the reefs. Quite often the anchor falls on the corals and if the boat drifts, then the anchor and the chain get dragged over the corals, breaking the branches or even uprooting entire colonies. In the case of large ships that anchor near the reefs for passenger and cargo traffic, the damage can be enormous. Imagine what would happen if a 20 to 30 ton giant broom sweeps the reef?

83. What other human activities affect corals?

Pollution. Corals are very sensitive to oil and metal pollution. If a reef happens to be near the effluent discharge point of any industry or near a harbour, then the reef is practically doomed.

Even seemingly unrelated onshore activities can kill corals. For example:

• Logging is a major land-based industry in Andaman and Nicobar Islands. As a result, huge quantities of mud and silt are washed off every monsoon on to the coastal zones. These settle on corals and kill them by smothering.  

• In the Gulf of Kachchh lots of mangroves have been cut. The mangroves have a mud - binding capacity. When the mangroves are cut, the mud-binding capacity is lost and the mud gets washed on to corals. This is a major cause of death of nearshore corals in this region.
  
• Thermal pollution, like hot water discharge from the cooling towers of industries or power plants near the reefs, can also kill them.

84. Does atomic radiation affect corals? I remember that some reefs in the Pacific were used as nuclear bomb test sites by USA and France.

We don’t know for certain about radiation effects because these sites are not accessible to civilian scientists. Undoubtedly, the shock waves of nuclear explosion must have killed corals. How much? Nobody would tell us that or let us find out.

85. The corals must be living a miserable life, aren’t they?

From every angle, yes. 

Even when you pay a visit to them you make their life miserable! The hotels meant to provide lodging for you may be built of coral stones, or may even be built on the reefs so that you don’t have to go too far to see them! With the tourism industry, comes the pollution - sewage, oil, plastics and other solid wastes. 

Even your reef walking can be harmful to corals; you may inadvertently step on them and break off their branches.