As corals die, watery grave awaits islands
Corals act as a natural barrier and protect the landmass from the sea; without them, the Indian peninsula would submerge, say experts.Updated: May 11, 2018 08:39 IST
Much like in many parts of the world, rising sea-surface temperatures because of global warming, aggressive fishing and increasing siltation due to deforestation are leading to the death of corals off India’s coast.
“In terms of diversity, India ranks fourth with around 21,000 species; the first being New Zealand with around 26,000 species, followed by China with around 25,000 species, and Australia, which is home to the great barrier reef with 24,000 species,” said K Venkataraman, former director of Zoological Survey of India (ZSI), the national centre for survey and exploration of the fauna across the country. “Some estimates say that by 2050, all the corals in the world will be dead,” he said.
Corals are among the oldest ecosystems on earth, coming into existence nearly 500 million years ago. They also support immense biodiversity — though coral reefs occupy 0.25% of the surface area of oceans, about 25% of the world’s fish species are dependent on them. “Worldwide, corals are estimated to support 3-10 million marine plants and animals, of which only about 1.8 million have been identified,” said Venkataraman.
Corals can grow under narrow environmental conditions — low level of nutrients, temperature between 22 and 26°C, salinity between 32 and 38 practical salinity unit with more than 90% water clarity and oxygen saturation.
In 2016, there was a loss of more than 23% corals off the coast of Andaman and Nicobar Islands when the sea-surface temperature rose due to El-Nino effect, which is the irregular periodic warming of the eastern Pacific Ocean that affects the climate in the tropical and sub-tropical regions. In a single year, the reef cover went down from 52.27% of all corals in India, to 39.94%.
Bleaching is a phenomenon where the corals — stressed by environmental factors such as rise in temperature, salinity, siltation, pollution etc — eject the symbiotic algae (zooxanthellae) from within their tissues, causing the coral to turn white. Since corals cannot produce their own nutrition and depend on symbiotic relations with zooxanthellae and marine protozoa for photosynthesising their nutrition, this loss leads to bleaching and finally death.
Bleaching is reversible if the environmental stress factors resolve.
“Corals can survive a bleaching event, but as they receive nearly 90% of their energy from organisms, it makes them prone to death,” said Dr CM. Ramakritinan, head of the department of marine and coastal studies at Madurai Kamraj University.
In 2010, India experienced one of the worst bleaching, when 81.84% of the corals in the Andaman and Nicobar islands were bleached. Again, Palk Bay, between Tamil Nadu and Sri Lanka, experienced an unusual bleaching event in 2015, when more than 30-50% of massive corals got affected. “The finger corals of the family Acroporidae died and distributed as broken pieces called coral rubble in and around the coral reef environment,” said Dr Ramakritinan. Elevated sea-surface temperature over a long four-month period in 2016 led to the death of 16% of the corals in the Gulf of Mannar.
Massive global coral bleaching incidents are becoming more frequent worldwide. A global study of bleaching events in 100 reef systems between 1980 and 2016 showed that the average interval between bleaching events has less than halved. The interval now stands at six years, which is too narrow a window for them to recover, according to the study published in the journal Science in January.
Large-scale coral deaths led to the proliferation of invasive species. After the 2016 bleaching incident in the Gulf of Mannar, scientists for the first time observed an outbreak of a parasitic sponge. “The dead corals became the breeding ground for the parasitic sponge Terpios hoshinota, which soon started flourishing and killing live corals. The sponges can tolerate much higher temperatures than the corals and they can thrive in dirty water, making it possible for them to proliferate in an environment too stressed for corals,” said Dr K Diraviya Raj, one of the scientists to have observed the phenomenon and an assistant professor at Suganthi Devadason Marine Research Institute, Tuticorin, Tamil Nadu.
“The 177 species of scleractinian (stony) corals in Lakshadweep’s atolls (ring-shaped reef enclosing a lagoon completely or partially) are mostly undisturbed by both natural and anthropogenic (human) aspects,” said Dr Kailash Chandra, director, ZSI.
Need for corals
Former ZSI director K Venkataraman narrates an incident where he was asked by a minister why corals had to be conserved, and he said, “without the corals, the Indian peninsula would submerge.”
“Corals act as a natural barrier and protect the landmass from the sea. The impact of coral reefs was clearly seen during the 2004 tsunami,” he added.
The shoreline of Tirunelveli, Tuticorin, Ramanathpuram and Sivagangai districts in Tamil Nadu were protected by the coral, according to a study by the Centre for Marine and Coastal studies published in 2007. “The chain of 21 islands in the Gulf of Mannar and the corals around them acted as baffles in absorbing the energy of the tsunami,” the study said.
A simulation study by Princeton University showed that a “sufficiently wide” barrier reef within a metre or two of the landmass reduces the run-up by up to 50%, depending on topography and wavelength of the Tsunami.
The loss will be fatal for Lakshadweep. “The existence and the carrying capacity of the Lakshadweep landmass is dependent on the formation of atoll reefs. The loss of corals will slowly destroy the structural affinity of the islands, leading to submergence,” said Dr Chandra.
The coastal population also depends on the marine resources from corals —fish, molluscs, and shells for artefacts —for livelihood. In the Andamans, tourism-dependent on the coral environment is the major source of livelihood.
“The loss of corals will result in the loss of great biodiversity in the areas. Corals are the natural heritage and rainforest of sea; it harbours 25% of the marine biodiversity,” said Dr Chandra.
Too Little too late?
Apart from documentation and exploration of coral cover and associated fauna, programmes for coral transplantation, creating nurseries, and studying the reproductive and regeneration patterns are underway.
There are no long-term projects or early warning systems that predict changes in sea-surface temperatures to help initiate interventions before the damage begins.
“Scientists have just been studying corals and doing nothing about the degradation. For example, the coral transplantation programme was just a demonstration that the corals from Gulf of Mannar could survive in similar conditions of the Gulf of Kutch, but once the programme was over, there was no maintenance for their survival,” said Venkataraman.
Of the Rs 2,675 crore budgetry allocation to the ministry of environment, forests and climate change in 2018, Rs 18 crore went to centrally-sponsored schemes for conservation of mangroves and corals. The 2019 budget made no allocation under the head, compared to Rs 365 crore for Project Tiger and Rs 27 crore for Project Elephant.
Targeted protection is anyway not enough. “It needs a holistic approach that factors in connectivity of freshwater, coastal, offshore and marine systems,” said Ema Fatima, senior programme officer, Ocean & Coast Conservation Programme, World Wildlife Fund-India. “I fear that when my grandchildren grow up and ask me where are the corals you worked so hard to conserve, there would be nothing left to show them,” she said.