Date: 14/04/2023 Shift: Q. No: 97

In a surprise find, scientists have discovered that coral reefs along the Gulf of Mannar off the coast of Tamil Nadu and Palk Bay, which suffered damage by mass bleaching earlier this year, have sprung back to life within a few months. The Gulf of Mannar is a 10,500 sq km biosphere, which has 21 islands replete with 128 species of colourful corals.

While studies have shown that coral reefs on the west coast in the Gulf of Kutch are bleaching away due to warmer waters, scientists from the National Centre for Coastal Research, under the ministry of earth sciences in Chennai, found that those on the east coast are bouncing back. Underwater images captured by the team showed nearly all damaged corals in Palk Bay have recovered while 85% of corals have regenerated in the Gulf of Mannar.

Coral reefs, the foundation of underwater ecosystems, providing food and protection for marine life, are under threat from elevated sea surface temperatures that lead to bleaching — corals turning white and expelling the microalgae that colours and nourishes them.

Scientists link a drop in sea surface temperature to quick revival of corals
Over the last few years, reefs around the world have suffered mass coral bleaching events as a result of increase in global surface temperature caused by greenhouse gas emissions. According to UNESCO, coral reefs in all 29 reef-containing World Heritage Sites would cease to exist by the end of this century if greenhouse gas emissions continue under a business-as-usual scenario.

Amid these grim predictions, the near-complete recovery of undersea forests in the east coast within months has brought cheer to scientists.

National Centre for Coastal Research (NCCR), which has been monitoring coral reefs along the Indian coast since 2000, found that corals which had bleached between March and June this year started to regain their colour in August.

The team monitored three locations — Mandapam, Keezhakarai and Palk Bay — during the bleaching event. “It’s surprising that we have seen almost complete recovery in such a short period of time,” said a scientist.

Scientists have attributed a drop in sea surface temperatures for the quick revival of corals. Sea surface temperatures had peaked between 32°C and 36°C earlier this year but dropped between 29.2°C and 30°C last month. Most reef-building corals grow in water temperatures between 23°C and 29°C, while only a few can survive in temperatures of 40°C or below 18°C. Corals can survive bleaching events, but die if they are under stress for longer periods — like in the case of reefs in Gulf of Kutch where frequent ocean heat waves or thermal stress due to climate change have taken a toll.