The below mentioned article provides an essay on coral bleaching.
Coral bleaching refers to loss of algae from the corals resulting into the white colour which is indicative of death of corals. Global warming has been reported as the major factor of coral bleaching. The coral bleaching during 1997-98 has been recorded as the most catastrophic event as it accounted for large- scale death of corals in the tropical oceans of 60 countries and island nations.
Though coral bleaching was observed by Alfred Mayer as back as 1919 but it was the year 1998 when large-scale coral bleaching accounting for 70 per cent death of corals off the coasts of Kenya, Maldives, Andaman and Lakshwadweep islands in the Indian Oceans and 75 per cent death in the Seychelles Marine Park System and the Mafia Marine Plant off Tanzania was reported by Clive Wilkinson of the Global Coral Reef Monitoring Network (GCRMN) of Townsville (Australia).
(1) Catastrophic bleaching adversely affecting 95 per cent of shallow water corals in Baharain, the Maldives, Sri Lanka, Singapore and Tanzania;
(2) Severe bleaching accounting for 50-70 per cent death of corals in Kenya, Seychelles, Japan, Thailand and Vietnam;
(3) Moderate bleaching resulting into 20- 50 per cent coral mortality but with quick recovery, and
(4) Insignificant bleaching or no bleaching.
The cases of large-scale coral bleaching have been reported in the Andaman and Nicobar islands of India. It may be pointed out that the areal coverage of coral reefs in India has been estimated to be 18,000 km2. The corals have mainly colonized around the Lakshwadweep and the Andaman and Nicobar islands. Besides, small patches of coral reefs are found in the Gulf of Kutch and the Gulf of Manar.
According to the study conducted by the Society for Andaman and Nicobar Ecology (SANE) based at Port Blair there has been mass coral bleaching (in 1998) around the Andaman reefs and 30-70 percent bleaching around the Nicobar reefs. This bleaching is related to 2°C rise in temperature from the normal temperature in the Andaman Sea in 1997-1998.
According to the study by National Institute of Oceanography (NIO) based at Goa the coral reefs of the Kavaratti and Kadamat islands in Lakshwadweep have suffered great damage from coral bleaching due to bacterial diseases and warmer sea temperature.
The corals in the Gulf of Kutch have been bleached due to siltation:
(1) Most of scientists have acknowledged global warming as the most significant factor of coral bleaching causing large-scale coral death. ‘According to the Global Coral Reef Alliance (GCRA) every known mass bleaching occurred when temperatures were just 1°C higher than normal during the warmest summer months’.
(2) EI Nino phenomenon has also been related to coral bleaching. It may be mentioned that the warmest year of 1998 was also associated with the strongest El Nino phenomon causing further warming of the Pacific Ocean waters. It may be pointed out that El Nino accounts for coral bleaching in certain localities only but the phenomenal increase in coral bleaching in the years 1983, 1987 and 1998 was also associated with strong El Nino weather phenomenon.
(3) The outbreaks of coral diseases (black band disease, coral plague, aspergillosis and white band disease) cause coral death.
(4) Local factors like increase in siltation of sea waters due to mass flux of sediments and nutrients brought by the steams from the erosion of high islands consequent upon land use changes; pollution of sea waters caused by industrial effluents, urban sewage and oil slicks; destructive fishing practices, over-fishing; clearing of marine forests around coral reefs; filling of wetlands (marine forests and wetlands trap sediments and filter pollutants and thus save corals from degradation); mining of coral rocks for building materials; collection of rare coral species etc. are also responsible for coral degradation at local and regional levels.
It may be mentioned that corals also have recovery characteristics. In the past inspite of large-scale climatic changes since Mesozoic era (200 million years ago) like Ice Age (Peistocene Ice Age), fluctuations in solar activities and several environmental stresses corals have managed to survive and recover. ‘Reefs will not become extinct in the long term, but a single bleaching event will take reefs between 30 to 100 years to recover’.
It is suggested that proper investigations and studies of coral ecosystems are necessary to understand the holistic view of association between coral ecosystems, global warming and coral bleaching so that the corals may be rejuvenated.