14% Drop in Coral Growth in Oceans

14% Drop in Coral Growth in Oceans

The effects of global warming have shown up in a definite way in the Great Barrier Reef of Australia. A research paper in the latest issue of ‘SCIENCE’ journal notes unprecedented effects of increased co₂ on the Great Barrier Reef. Scientists found the rate at which corals were able to build skeletons droped by 14 per cent during the periods of study 1993 till 2008

Coral reefs are considered as the rain forests of the ocean as they support great biodiversity. Any drop in growth of the reefs of the Great Barrier Reef is hence worrying.

What makes the study significant is that scientists studied 328 colonies from 69 reefs, and the duration of study was 15 years. This study shows that the effects are probably large scale in extent and the observed changes are unprecedented with the last 400 years. The growth of coral reefs depends on their ability to build skeletons. These skeletons are built by calcification of calcium carbonate. There are a few things that may affect the calcification process.

Though the scientists note that the precise cause of decline in calcification are not known, their study suggests that increased temperature stress and increased acidity of seawater are the most likely causes.

Coral reefs are extremely sensible to sea surface temperature. Any change beyond 1^oc for extended periods of time affects the corals. Increase in sea surface temperature affects and destroys the symbiotic zooxanthelle algae that live on the corals. Any damage to the algae leads to a loss of the symbionts and a rapid whitening of coral host (thus the term bleaching). Mass coral bleaching was not documented in the scientific literature before 1979. 1998 saw a large scale destruction of coral reefs all over the world.

Since oceans act as sinks for carbon dioxide, increased uptake of CO₂ by ocean water will make them acidic. Supersaturation of tropical sea water with calcium carbonate is crucial for reef calcification process. Hence, acidic water will compromise supersaturation.

The pH of the ocean has decreased by 0.1 unit (becomes acidic) since the beginning of the industrial revolution. And this has affected the calcification process. Studying the skeleton density allowed the researchers to calculate the amount of calcification annually. They found that the calcification rate rose to 504 per cent between 1900 and 1970. It dropped by 14.2 per cent between 1993 and 2008. The drop was mainly due to growth slowdown from 1.43 cm a year to 1.24 cm.

How the sea surface temperature and lower pH would affect the reefs and marine organisms in the long run, cannot be accurately predicted, since living organisms and sea are dynamic. How the increased temperature, acidity and reduced skeletal strength, due to calcite erosion, would affect marine life are not known.