Finding shows Lakshadweep’s coral reef is recovering from the stress experienced after the 2010 El Niño
After the extensive damage to coral reefs reported across the globe in 2010, there is some news to cheer. For the first time coral spawning, popularly referred to as “sex-on-the-reef”, has been recorded scientifically in India in the south-western coast of Lakshadweep.
Coral spawning is sexual reproduction of corals, which involves mass collective expulsion of colourful eggs and sperm clouds into the water by corals. Normally an annual occurrence, the gametes then rise to the surface of the ocean, creating a colourful slick. It is usually observed after full-moon nights.
Survey by Wildlife Trust of India (WTI) showed that the larvae were seen forming slick-like layers around four islands—Agatti Island, Bangaram, Thinakara, and Kavarrati.
The slick was first observed by WTI marine biologist S Subburaman last week, and also by the Central Marine Fisheries and Research Institute (CMFRI) team. Subburaman, who on a boat when he first noticed the slick, collected some pink and brown spawn for examination. He along with CMFRI scientists Jasmine and R Srinath examined the samples and confirmed that they were indeed coral spawn.
Record warm ocean temperatures across much of earth’s tropical oceans during the summer of 2010 had created the second worst year globally for coral bleaching. Coral bleaching is a whitening of the corals that occurs when factors such as high water temperatures, increased water acidity or pollution disturbs the symbiotic relationship between the corals and the algae that live inside them. Bleaching episodes occur when ocean temperatures rise above 29.5– 30.5°C .
According to National Oceanic and Atmospheric Administration (NOAA), El Nino of 2010 was the second worst year for coral bleaching on record since 1998, when almost 16 per cent of the world’s reefs were killed. The summer 2010 bleaching episodes were worst in Southeast Asia, where El Nino warming of the tropical ocean waters during the first half of the year was significant. In Indonesia’s Aceh province, 80 per cent of the corals died, and Malaysia closed several popular dive sites after nearly all the corals were damaged by bleaching.
Environment wardens Abdul Raheem and Sayeed Ali said that this finding proves that Lakshadweep’s corals are recovering from the stress they experienced after the El Niño of 2010. Chief wildlife warden of Lakshadweep, Thirunavukarasu, added that it’s great news that the Lakshadweep coral reef is in a healthy state.
During spawning, the eggs are fertilised and form larvae. The larvae then float off till they find suitable substrates, settle and form their own colonies, helping corals thrive.
Coral spawning is a big tourist attraction in the Great Barrier Reef in Australia, where it generally happens soon after the full moon in November or December. In the Maldives, spawning has been scientifically determined to take place between the end of January and the beginning of March. One thing is universal though – exact date of spawning is still largely unpredictable. It was first recorded in 1981.
Alasdair Edwards, professor at Newcastle University in the UK, said that the spawning has been spotted much earlier than expected. “We expect corals to spawn a week after full moon nights in March (27th for this year) or April (25th for this year),” he said. “This event also shows that corals spawn in day as well, though not as commonly as at night.”
According to a report by the World Meteorological Organization and the Convention on Biological Diversity, the large amount of CO2 humans have put into the air in recent decades has done more than just raise Earth’s global temperature—it has also increased the acidity of the oceans, since CO2 dissolves in sea water to form carbonic acid.
Corals have trouble growing in acidic sea water, and the combined effects of increasing ocean temperatures, increasing acidity, pollution, and overfishing have reduced coral reefs globally by 19 per cent since 1950. Another 35 per cent could disappear in the next 40 years, even without the impact of climate change. Coral loss has been the most severe in Earth’s hottest ocean, the Indian Ocean. Up to 90 per cent of coral cover has been lost in the Maldives, Sri Lanka, Kenya and Tanzania and in the Seychelles. Global warming has heated up most of the tropical ocean surface waters by about 0.5 degree Celsius over the past 50 years, and the remarkable bleaching episodes of 1998 and 2010 both occurred when strong (natural) El Nino episodes heated up Pacific tropical waters to record levels.
B C Choudhury, senior advisor for WTI, said that the positive news of widespread coral spawning comes at a time when a lot of pessimism surrounds the state of our corals—with talk of them getting bleached, their habitats being destroyed, global warming, sea levels rising and so on. “It is really a magnificent sight, and the team of scientists at Lakshadweep was really fortunate to witness it. It should give impetus to others working with corals to look out for their seasons of spawning, and encourage people to monitor these beautiful organisms on a larger scale,” he added.
Spawning normally happens when the water is warm, and when the tide is changing from high to low. “Different species spawn at different times and follow different patterns,” said Choudhury. “Much more research needs to be done to understand the process clearly.”
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